P1870 Hard1-2 Shift....please help

so after ive been on the freeway or drove for awhile I have a hard 1 to 2 gear shift. took it to a little autoshop while I was out of town (light came on while i was on roadtrip) and they gave me the P1870 transmission component slippage code.

I have read that this means its the TCC and/or the control valve body that is worn and needs replaced.

My question is.....when this code is displayed is it usually the valve body & TCC that need to be replaced? or is it possible that just one of the two are bad?..I dont understand why the man at the garage didnt tell me exactly what the problem was (as in "you need this part...."). he just told me this code. Is further testing needed to determine or is this a pretty open shut case? And if so when I go into a transmission shop and tell them my story are they going to look at me like I have two heads....since i didnt get it diagnoticed with them or are they use to that?

the TCC is inside the control valve body correct? my 99 blazier has 165000 miles on it...so chances are both are worn. whats the repair cost on this thing run? ive been contemplating jus ignoring it and driving it with the light on. I dont have a grand to spend.

any ideas? thank you!

Don't drive with that light on, will destroy transmission. I had the P1870 a month ago in my 99 blazer. its a common problem. What happens is there is a check ball in on of the passageways in the tranny(cant think of tech term off hand) but when the tranny is up to temp this ball will stick and that is what causes the computer to command full line pressure to the tranny and thus hard 1-2 shift. After fixing mine my gas mileage on the highway went up 7 mpg.


http://www.google.com/search?hl=en&q=P1870+shift+kit Google search on it

http://cgi.ebay.com/ebaymotors/TRANSGO-4L60E-SHIFT-KITw-PWM-VALVE-INSIDE-TO-FIX-1870_W0QQitemZ260032260021QQcmdZViewItem


What my mechanic did and what you can have done depending on what your tranny fluid looks like is that. That is the recommended easy fix for it. You could also replace the valve body with an updated GM valve body but thats a tad more pricey. This kit can be done with it in the vehicle. My mechanic charged a little over 300 bucks for parts and labor, I only paid 117 since it was under warranty. If you do a search under the problem diagnosis and or look in how to--> index (table of contents) there is a TSB on this site for it and or I could send it to you since I have them here.


http://www.my3cents.com/showReview.cgi?id=12520


http://www.google.com/search?hl=en&q=P1870


Don't let them sell you a rebuild or a jyd tranny unless it is absolutely necessary but the longer you drive with that condition the more likely it will grenade.

Welcome to AF.
What year and what mileage is on it?
Has the transmission filter ever been serviced?
How is the fluid level and condition?

In answer to your question about the code.
It is set when a component slipping or transmission slipping.
Which is not good.
Computer control problems can cause it but most of the time it is internal transmission problems.
Some people work on the valve body and TCC convertor.
And do get the code off for a while.
But Valve body repair is only a band aid to the real problem.

First thing besides a transmission service is to take it to a good repair shop and get it on a good transmission /engine capable scanner and find out where or what the slippiage is.

And go from there.
Good luck
MT

Here is one of the first steps in testing on the code.

Diagnostic Information on DTC P0894 and P1870 #02-07-30-001A - (02/11/2004)
Diagnostic Information on DTC P0894 and P1870
2000-2004 Passenger Cars and Light Duty Trucks
2003-2004 HUMMER H2
with 4L60-E or 4L65-E Automatic Transmission
This bulletin is being revised to include additional model years and additional diagnostic information. Please discard Corporate Bulletin Number 02-07-30-001 (Section 07 -- Transmission/Transaxle).
Diagnostic trouble codes (DTC) P0894 and P1870, Transmission Component Slipping, may have different root causes. The following diagnostic tips are provided to assist in accurately repairing the condition.
Corporate Bulletin Number 01-07-30-023A, dated November 2001, is intended for 1996-1999 vehicles with more than 32,000 km (20,000 mi). This bulletin addresses wear in the valve body TCC isolator/regulator bore, which can cause DTC P1870. This wear condition is not the cause of DTC P0894 or P1870 on any 2000 model year vehicle built after January 15, 2000, or any 2001 or newer vehicles as the valve body used on these vehicles has been revised to prevent the wear condition.
Corporate Bulletin Number 99-07-30-005, dated March 1999, should be used to help with diagnosis of these DTC's. This bulletin will help to determine if the DTC is caused by the TCC system or by a slipping internal transmission component such as a clutch or band.
Slip speeds greater than about 250 rpm at steady state driving are caused by a slipping clutch or band.
Slip speeds below 250 rpm at steady state driving are usually caused by the TCC not applying but may also be caused by a slipping clutch or band.
A plugged or restricted TCC apply fluid orifice (238, located in the pump) may cause DTC P0894 or P1870, especially in low mileage vehicles with less than 8,000 km (5,000 mi).
A converter clutch valve (224, located in the pump), which does not have full travel of 13 mm (0.5 in) or is stuck in the off position may cause DTC P0894 or P1870. Inspect the valve for chips, debris, nicks or burrs. Also, inspect the springs (225 and 226) to make sure they are not limiting valve travel. A spring that is not fully wound may catch in the bore, limit valve travel and cause DTC P0894 or P1870.
A cracked or leaking TCC solenoid (part of harness 66) may cause DTC P0894 or P1870. Use solenoid test kit J 44246 to test the operation of this solenoid.
A cracked or leaking TCC PWM solenoid (396) may also cause DTC P0894 or P1870.
When attempting to diagnose a DTC P0894 or P1870, it is important to also refer to the appropriate Service Manual for further possible causes of this condition.

hey there...thanks for all the chime ins....appreciate it....i checked out that gear shift on ebay, I would have no idea how to install that if I bought it. Besides wouldnt that be like putting on a bandaid for the problem? Id rather not do that........the blazier is a 99...and yeaaaa........its got about 165,000 miles on it.....so its old.....apparently 1870 could mean many different things? Ive read numerous places its usually the valve body, but who knows. I guess Ill take it to a transmission shop. I HATE paying ANOTHER person 100 bucks to tell me whats a matter with it.....pisses me off....I guess if its the tranmission and its gunna cost a grand or more I wont get it done. I dont see much point in spending that much for a car that has 165000 on it...course I dont know how long chevys really last, mileage wise. I would say my blaziers time is about up? i dunno.......stupid chevy!

This wear condition is not the cause of DTC P0894 or P1870 on any 2000 model year vehicle built after January 15, 2000, or any 2001 or newer vehicles as the valve body used on these vehicles has been revised to prevent the wear condition.


mines a 99....before the valve body was revised....so whats that mean?? ...I dont think I get the whole concept of the valve body. as in whats inside of it etc....is it possible for the valveB to be worn but still function properly and something internal is having the problem? or....no? lol

It is the valve body. Some describe that kit as a bandaid but its what most mechanics recommend using. Mine did and Ive had no ill effects with it since and Ive driven it a bunch since then.

MT2500 nice job summarizing the links i provided :)

how long have you been driving it? miles? did u buy it online and then take it to a mechanic? ...... if buying that online and then taking it to a shop to be installed is an option. i would like to consider it. THAT isnt that expensive. even if it buys me just a year.

mines a 99....before the valve body was revised....so whats that mean?? ...I dont think I get the whole concept of the valve body. as in whats inside of it etc....is it possible for the valveB to be worn but still function properly and something internal is having the problem? or....no? lol

The newer valve body has a harder valve and valve nody case bores to prevent wear.

Internal transmission wear is the root of the problem.

Internal wear causes the valve body valves to work and olsolate more wearing the valve body.

Some times a valve body repair will band aid it for some more miles.
But it does not fix the main problem.
A good transmission with a good scanner can find the main problem or where the slippage is.
Sometimes it is even electrical or pcm problems.

I would also pull the oil pan and see what is inside it and service the filter to start with.
You can tell a lot by looking in the pan and open up the old filter and see what kind of stuff is in there.

Has it ever been serviced?

so after doing alot of research on the shift kit (thank you) I suppose im feeling pretty confident on the matter. I just read

"What are my options to fix this problem? Rebuild the transmission. Although the most expensive fix, a full transmission rebuild could be the best fix for you if your car is high mileage and you plan to keep it a lot longer. If you've got 150k on the transmission already and plan to keep it for another 100k, you will be needing a rebuild in the future anyway. Be sure to repair/replace that valve!"

as stated earlier i got 165000, what do you think I should do? do you think that kit will prolong the life for another year even tho it has 165000...its always been realtively good takin care of..,...transmission fluid, oil etc etc...

The newer valve body has a harder valve and valve nody case bores to prevent wear.

Internal transmission wear is the root of the problem.

Internal wear causes the valve body valves to work and olsolate more wearing the valve body.

Some times a valve body repair will band aid it for some more miles.
But it does not fix the main problem.
A good transmission with a good scanner can find the main problem or where the slippage is.
Sometimes it is even electrical or pcm problems.

I would also pull the oil pan and see what is inside it and service the filter to start with.
You can tell a lot by looking in the pan and open up the old filter and see what kind of stuff is in there.

Has it ever been serviced?

when this problem first came up I got the transmission fluid flushed and replaced and turned off the SES. after about 80 highway miles the light came back on. its been pretty good taken care of its 165000 miles. im off to work ill check this thread later.....thanks guys! later

Was the code cleared and is it the same code back?
Was the filter changed with the flush?
It needs to go on a scanner and find the actual cause of the code or actual transmission slippage.

Flush is a no no on a high mileage transmission.

Good Luck
MT

Info - Component Slipping/DTC P1870 - Diagnosis #99-07-30-005 - (03/18/1999)Table 1: TCC System Symptom Table Table 2: Internal Transmission Symptom Table Component Slipping/DTC P1870 - Diagnosis1996 Buick Roadmaster 1996 Cadillac Fleetwood 1999 Cadillac Escalade 1996-99 Chevrolet Camaro, Corvette 1996-99 Pontiac Firebird 1996-99 Chevrolet and GMC C/K, M/L, S/T, G Models 1996-99 Oldsmobile Bravada 1996-99 Holden Commodore with Hydra-matic 4L60-E (RPO M30) DescriptionMany technicians experience difficulty when diagnosing 1996-1999 4L60-E transmissions with a DTC P1870 (Transmission Component Slipping). The purpose of this bulletin is to provide assistance for technicians that have already completed the DTC P1870 diagnostic table in the Service Manual. This bulletin will provide a diagnostic strategy for solving DTC P1870 concerns as well as give some of the most common causes for a DTC P1870. General Information ImportantChevrolet Camaro, Pontiac Firebird with 3.8L V6 Engine experiencing a slip condition at 70-90 km/h (45-55 mph) when the TCC applies should refer to Corporate Service Bulletin 77-71-70A for calibration re-flash. 1996 Chevrolet and GMC C/K, M/L, S/T, G Models, and 1996 Oldsmobile Bravada with VCM and 4L60-E (RPO M30) with a slip or flare on the 1-2 and/or 2-3 upshift, or no 3rd or 4th gear, or launch shudder should refer to Corporate Service Bulletin 66-71-03A to ensure that a poor internal ground in the VCM does not exist. A DTC P1870 indicates that a mechanical malfunction exists. If any other DTC's set along with a DTC P1870, then diagnose those first. A DTC P1860 (TCC PWM Solenoid Circuit Electrical) will set if a TCC PWM solenoid circuit failure exists. A DTC P0740 (TCC Enable Solenoid Circuit Electrical) will set if a TCC enable solenoid circuit failure exists. When attempting to duplicate DTC P1870, it is critical that a normal operating temperature of 82°C (180°F) to 93°C (200°F) be reached. It may be difficult to attain the transmission temperature required to adequately cause the DTC to duplicate. Allow the vehicle to idle to assist in warming the powertrain. Optimum speed to duplicate the DTC P1870 is between 89 km/h (55 mph) and 107 km/h (63 mph). Commanding the TCC ON and OFF several times with the Tech II is critical to monitoring slip when sticky valves in the valve body are suspect. If the customer brought in the vehicle for a temporary harsh 1-2 shift and no driveability concerns are seen during a test drive, then remember that a harsh 1-2 is a result of the PCM commanding maximum line pressure from recognizing a DTC P1870. The PCM must recognize that a DTC P1870 has set in two consecutive key cycles to illuminate the MIL. If a DTC P1870 is not recognized on a second key cycle, then normal line pressure returns. Vehicles should be inspected for correct tire size, axle ratio, or calibration. Diagnostic ApproachActionYesNoAttempt to duplicate DTC P1870. Did you duplicate DTC P1870?Go to Slip Check ProcedureGo to TCC System Symptom TableSlip Check ProcedureThis procedure will assist in isolating what area of the transmission is causing your slip, either the TCC system or internal transmission components. After you have isolated the origin of the slip, then utilize the TCC System Symptom Table or the Internal Transmission Symptom Table of this bulletin for most common concerns. To check for a TCC system concernTCC slip can occur either hot or cold or in both conditions. First, perform the following test at cold transmission temperatures, then perform the same test at normal operating temperature. Ideal slip from the transmission with the TCC applied is 50 RPM or less under light to normal throttle, no heavy engine load or hard accelerating conditions. Use the Tech II scan tool to monitor TCC slip while driving the vehicle in 4th gear at steady speed with the TCC commanded ON. When the TCC is applied or released (release the TCC with brake pedal, not the scan tool - release the TCC by lightly applying the brake pedal while simultaneously maintaining a steady throttle position), the slip speed should drop or rise 150-300 RPM. If the slip speed does not drop, then the DTC P1870 is being caused by the torque converter system. ActionYesNoDid TCC slip speed drop (150-300)?Continue Slip Check Procedure for an internal trans concernGo to TCC System Symptom TableTo check for an internal transmission concernSlip should be checked in every gear to isolate in which gear the slip may be occurring. Drive the vehicle in each forward gear range D1, D2, D3 and D4. Command the TCC ON with the Tech II in each gear and monitor slip speed. ImportantVehicle speed must be over 11 km/h (7 mph). Some TCC slip is normal when the TCC applies directly after 11 km/h (7 mph) is reached. If the slip speed remains constant from gear to gear, then the condition is most likely TCC related. Example: Slip speed is higher in second and fourth gear than in third gear. This would lead a technician to a possible slipping band. ActionYesNoIs slip speed equal in all gears?Go to TCC System Symptom TableGo to Internal Transmission Symptom TableImportantThese symptom tables are to be used when the following symptoms are associated with a DTC P1870. TCC System Symptom Table SymptomCausesTCC SLIP (100 RPM SLIP)Check for bronze bushing material in the pan and filter. If bronze material is present, then the stator bushings (234) and turbine shaft (241) should be replaced (Bronze bushing may turn black with an acrid odor). The turbine shaft and housing (621) should be replaced if damaged. In rare instances, it may be necessary to check for an overheated torque converter (24) (Blue and/or distorted converter). TCC solenoid (66) - Perform leak check. Converter clutch valve (224) in pump should be checked for 13 mm (0.500 in) of bore travel without binding. Turbine shaft O-ring seal (618) cut. Turbine shaft hole not drilled to full depth. This concern can be checked by squirting trans fluid through the turbine shaft hole to check for full flow. This is a low mileage failure. NO TCC APPLY (300 RPM SLIP)Converter clutch valve (224) stuck closed (Check for debris in valve bore). TCC PWM solenoid (396) broken/cracked. Visually inspect solenoid. TCC solenoid (66). Perform leak test. Turbine shaft O-ring seal (618) omitted. TCC SLIP WITH STALL STUMBLEConverter clutch valve (224) stuck open (TCC is applying).INTERMITTENT TCC, OK COLD, SLIPS HOTTCC PWM solenoid (396). Leak test solenoid. The TCC regulator apply valve (380) and/or converter clutch shift valve (224) may be sticking/side-loading. It is possible there will not be any damage to the valve upon inspection. Transmissions produced after 2/1/98 will have a groove cut into the spring end of the regulator apply valve. This design is to help float the valve in its bore (replace valve body assembly). Internal Transmission Symptom Table SymptomCauses3RD OR 4TH GEAR SLIP3-2 downshift solenoid (394) ball seat retention failed. Leak test solenoid. Usually associated with a 3-4 clutch/band worn. 3rd accumulator retainer and ball assembly (40) leaks. Test for proper check ball operation. Usually associated with burned 3-4 clutch. NO 4TH OR SLIPPING 4TH Check ball in the wrong location or extra check ball that has dropped behind the spacer plate during trans assembly. The extra check ball can block the 4th apply servo feed. Clutch orifice cup plug (238) not fully pressed in. SLIP/FLARE IN ANY GEARPump slide inner spring (207) or outer spring (206) omitted causing a slow slide response.NO 3RDClutch orifice cup plug (238) blown out.HARSH 1-2 UPSHIFT4-3 sequence valve (383) stuck in bore by sediment.NO 2-3 UPSHIFT2-3 shift valve (368) or 2-3 shuttle valve (369) stuck in bore by sediment.NO 3-4 UPSHIFT3-4 shift valve (385) stuck in bore by sediment.Service InformationRefer to the appropriate Service Manual for replacement procedures. Warranty InformationLabor Code: Refer to Labor Time Guide for correct labor operation. Please use the closest available labor operation for the diagnosis performed. GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition.

Here is a quote from one of the top transmission men.


In a nutshell, the valve body does chronically wear in the 4L60E especially in the lockup PWM bore. The code lights when there is more then 100 rpm or so when locked up. Depending on mileage and fluid condition will determine the next course of action. The seal on the input shaft gets tons of heat and is the most critical seal in the trans. If there are high miles, usually what it takes to wear the vb, then the rubber seals as well as the Teflon ones are just as worn. The 1870 code is telling me there is a internal leak in this trans...someplace. The transmission is a multitude of leaks and it is engineered that way, some are good leaks because they lube planetaries and some are not so good because they make the pump work harder to make up for the leaks inside. Teflon rings leak to get enough holding power to not leak. The point here is if you have excessive or extra leaks then the PWM must cycle higher pressure and volumes to compensate making it work harder and the very forces that wear out the vb bore are increased wearing the bore quicker. In addition to that factor, with internal leaks you also have increased temperature and heat kills big time in a tranny plus it decays the additives in the fluid itself and now you are in a downhill spiral as the trans self destructs form leaks and heat and destruction of the fluid itself. Now the hard parts will start to wear at an increased speed, the pump is trying to maintain for the fluid loss(leaks), the planets will start overheating as the bushings wear out you generate more hemorrhaging and more damage.
Yes, at that point the vb is a bandaid, it may solve the problem for now but the internal wear and hardening of the seals is still there and will continue to wear. The problem I have with just throwing a vb at this problem is simply, the worn components will make the new vb work harder and cycle more than it should and the consequence of that is another prematurely worn out vb and ultimately overhaul of the trans that you should have taken care of before. The transmission is a complete and interdependent unit meaning all parts rely and interact on each other. If one part is worn out then you must deal with the unit on the whole. There are exceptions to every rule and the jeep is a good one, the accumulator plate is held down by too few screws and the plate is under enough pressure that when the screws break, the plate peels back like a lid on a dog food can. If caught soon enough then a repair of the valve body is sufficient to be a complete repair. If you have a 4L60E with 100k on it and smokey fluid and only a P1870 then you are not doing the customer a service by simply replacing the vb.
I have yet to take a trans apart that was simply coding 1870 and not found hard seals or other problems internally. Most of the time, I have not even needed to deal with the vb at all, aside from basic clean up and solenoid replacements. I have had to replace more transfer plates than valve bodies from the balls eating through. In the past 6 months, I have replace 2 valve bodies. I do not use the sonnex kit although the place I get my vb's from does.
I hope this helped you understand why I claim the 1870 code means internal problems more than just throwing a vb in my experience.

Ive got about a 1000 miles on it since. When my pan was dropped, the fluid was fine.

Here's my experience with this DTC 1870 on my '95 blazer. So my truck had that code and the previous owner just drove it for a while until the 3-4 clutch burnt up and the trans no longer had 3rd or 4th gear. So they gave me the blazer for free and I rebuilt the transmission. I drove it and knew the converter wasn't locking up when the trans was warmed up and I was right when that 1870 dtc came back a short time later. So I ended up replacing the valve body and now the problem is solved. Hopefully you'll find this story helpful.

Here is a quote from one of the top transmission men.


In a nutshell, the valve body does chronically wear in the 4L60E especially in the lockup PWM bore. The code lights when there is more then 100 rpm or so when locked up. Depending on mileage and fluid condition will determine the next course of action. The seal on the input shaft gets tons of heat and is the most critical seal in the trans. If there are high miles, usually what it takes to wear the vb, then the rubber seals as well as the Teflon ones are just as worn. The 1870 code is telling me there is a internal leak in this trans...someplace. The transmission is a multitude of leaks and it is engineered that way, some are good leaks because they lube planetaries and some are not so good because they make the pump work harder to make up for the leaks inside. Teflon rings leak to get enough holding power to not leak. The point here is if you have excessive or extra leaks then the PWM must cycle higher pressure and volumes to compensate making it work harder and the very forces that wear out the vb bore are increased wearing the bore quicker. In addition to that factor, with internal leaks you also have increased temperature and heat kills big time in a tranny plus it decays the additives in the fluid itself and now you are in a downhill spiral as the trans self destructs form leaks and heat and destruction of the fluid itself. Now the hard parts will start to wear at an increased speed, the pump is trying to maintain for the fluid loss(leaks), the planets will start overheating as the bushings wear out you generate more hemorrhaging and more damage.
Yes, at that point the vb is a bandaid, it may solve the problem for now but the internal wear and hardening of the seals is still there and will continue to wear. The problem I have with just throwing a vb at this problem is simply, the worn components will make the new vb work harder and cycle more than it should and the consequence of that is another prematurely worn out vb and ultimately overhaul of the trans that you should have taken care of before. The transmission is a complete and interdependent unit meaning all parts rely and interact on each other. If one part is worn out then you must deal with the unit on the whole. There are exceptions to every rule and the jeep is a good one, the accumulator plate is held down by too few screws and the plate is under enough pressure that when the screws break, the plate peels back like a lid on a dog food can. If caught soon enough then a repair of the valve body is sufficient to be a complete repair. If you have a 4L60E with 100k on it and smokey fluid and only a P1870 then you are not doing the customer a service by simply replacing the vb.
I have yet to take a trans apart that was simply coding 1870 and not found hard seals or other problems internally. Most of the time, I have not even needed to deal with the vb at all, aside from basic clean up and solenoid replacements. I have had to replace more transfer plates than valve bodies from the balls eating through. In the past 6 months, I have replace 2 valve bodies. I do not use the sonnex kit although the place I get my vb's from does.
I hope this helped you understand why I claim the 1870 code means internal problems more than just throwing a vb in my experience.

alright, well thank you....that was kind of depressing advice. Kinda made me loose hope. I guess Ill just get it scanned at a transmission shop. All theyre gunna say is "yeah you need this, you need that....its gonna be 1800" :rolleyes:
I might just get the shift kit, get it installed. Drive it till it is no-more.

Here's my experience with this DTC 1870 on my '95 blazer. So my truck had that code and the previous owner just drove it for a while until the 3-4 clutch burnt up and the trans no longer had 3rd or 4th gear. So they gave me the blazer for free and I rebuilt the transmission. I drove it and knew the converter wasn't locking up when the trans was warmed up and I was right when that 1870 dtc came back a short time later. So I ended up replacing the valve body and now the problem is solved. Hopefully you'll find this story helpful.

That was my initial thought on repairing. What I was going to do. Replace the valve body. But I get so many conflicting answers from people all the time, online and not. That Im kinda if'y. So Im just going to start from square one again I guess and get it tested. If the problem is too expensive and the kit will work for the time being...well then....put that baby in.

alright, well thank you....that was kind of depressing advice. Kinda made me loose hope. I guess Ill just get it scanned at a transmission shop. All theyre gunna say is "yeah you need this, you need that....its gonna be 1800" :rolleyes:
I might just get the shift kit, get it installed. Drive it till it is no-more.


Glad to see you weighing all of the facts and pros and cons on it.
Yes find a good honest repair shop and get it checked out.
May be a minor or major problem.
Some transmission chain stores are a little rebuild happie.
Which ever way you go.
And let us know how it goes.
Good Luck
MT

If you like go ahead and let someone sell and replace your transmission but here is my suggestion! Check around and see if you can find a minor vacuum leak! This can simply be the big round hose that goes from the fuel injection to the power brake hub! This is normally a push in connector which has about a 1/2 inch hose clamped on it! If there is any kink or the connector is not in correctly a leak will occur and the transmission will shift rough as though you will be thrown out of the vehicle! Try unplugging this connector and plug it back in hard and straight and maybe you will be lucky and fix your problem. If the vacuum is correct your transmission will shift better than you have ever experienced!

Yes i too have had the p1870 code. drove mine for 20,000 miles of rough shifts. a friend told me to have the valve body reamed and a sleeve put in. which they did and the mechanic said i was VERY LUCKY to have made it this long. i have driven for 1000 miles now and all is well. i now get 22 mpg hwy compared to 19 - 20 before.

Yes i too have had the p1870 code. drove mine for 20,000 miles of rough shifts. a friend told me to have the valve body reamed and a sleeve put in. which they did and the mechanic said i was VERY LUCKY to have made it this long. i have driven for 1000 miles now and all is well. i now get 22 mpg hwy compared to 19 - 20 before.

This post is old and dead.
Always check date on a post and if old.
Let the dead rest in peace.
The valve body repair is only for certian years.
But a code 1870 almost always goes back and come back to internal transmission pressure leakage.
transmission trying to overcome pressure /lose or leakeage is what causes the valve body to wear out.

Now I know that this is old, but I have read this over and didn't realize the dates, but I thought I'd add some info on here, in case anyone is searching the P1870 code. The P1870 is a trans componenent slipping, it doesn't give a specific part problem, and can literally be many different things. That said though, usually, in my experience, the problem can be traced to either the torque convertor itself, or the circuit that controls lock-up, in this case, as was said in an earlier post, the TCC Regulator Valve and/or PWM solonoid.

The 4L60E from '95 and up had a controlled, gradual torque convertor lock-up, not the on and off lock-up found in earlier versions. When the convertor is signaled by the PCM to begin lock-up, this is done in percentages, all the way to complete lock-up. The PCM monitors lockup by sensing the different speeds the engine is turning, as to what the drive shaft is turning, this difference in speed is what the PCM keeps track of. If they are too far off and are out of range thats when the P1870 comes up, as slippage, or too big a difference in speeds between the engine and transmission is sensed, and in turn the PCM commands max line pressure in an effort to reduce or eliminate the slippage it is sensing. The idea behind this was to try and save the transmission, to limp it home, without overheating it as a result of slippage. Thats why driving a vehicle with a p1870 will usually burn up a trans, because max line pressure puts a lot more stress on the internals, eventually damaging something internally.

All the valve bodies from GM, even the "updated" ones eventually go bad. All GM did to update the valve bodies was by replacing the TCC regulator with a bigger one and reboring the valve body. You can tell if the valve body was a serviced unit as these valve bodies were stamped with "serv" on them. The problem is the valve body is made of aluminum. The valve rubbing on the aluminum valve body wears those spots and causes oil pressure to leak at that point. When the PCM commands the PWM to start ramping up lock-up of the convertor, the TCC regulator cannot be controlled as its leaking to much oil past it, causing the convertor to lock up to slowly, if at all. The PCM sees the difference in speed between the engine and trans and boom your 1870 pops up.

Now if the trans was not run bad and hasn't been driven to long with the P1870 and proper diagnosing leads to the TCC regulator as the possible problem, then usually replacing the valve body or using an aftermarket fix(i always prefer the sonnax update) will get you going again. Shops don't always prefer this route because if they try this and a couple weeks it (the vehicle) comes back again with the same p1870, then its kinda hard to now tell the customer they need to rebuild their trans.

Now again like it was said before, the P1870 can mean a few things, so proper diagnosing is important, but the 4L60E P1870 almost always leads to the convertor, and/or its oil circuit and related parts. Hope this helps someone in figuring out the dreaded P1870.