2001 blazer "service engine soon" came on. code was tranny slip. Tranny Shifts Hard After Long Drive. turn off and restart after 5 seconds and no problems. drive for a week around town and works fine. go for a long drive (40 miles) again about 65 to 75 mph. i slow down and stop in the next town and accelerate and shifts hard from 1st to 2nd and 2nd to 3rd under easy acceleration...feels like a shift kit. turn off and restart again after 5 seconds and something resets and no problem again until a long highway drive. spent hundreds at the local chev dealership and they are not able to diagnose. we changed the tranny fluid and no change.

If you'll do a search of this board.....there's alot of posts about your problem. The common thing seems to be a solenoid(s) in the tranny (PWMTCC). Costs about $35-40 a piece if they have to be replaced. The dealer is trying to screw you (or already has). Take it to a different place and have someone who knows what they're doing look at it.

2001 blazer "service engine soon" came on. code was tranny slip. Tranny Shifts Hard After Long Drive. turn off and restart after 5 seconds and no problems. drive for a week around town and works fine. go for a long drive (40 miles) again about 65 to 75 mph. i slow down and stop in the next town and accelerate and shifts hard from 1st to 2nd and 2nd to 3rd under easy acceleration...feels like a shift kit. turn off and restart again after 5 seconds and something resets and no problem again until a long highway drive. spent hundreds at the local chev dealership and they are not able to diagnose. we changed the tranny fluid and no change.

Hate to say it, but this sounds like the ignition switch causing the problem.

It is a black module in the steering column.

Swap it out.

It is known to cause transmission problems, engine problems and the works.

I had the same problem with my blazer. Your problem is your valve body. When your tranny gets hot the valve body compresses causing your hard shift. You need a new valve body kit and your valve body drilled out with a sonnex drill bit. Typically runs around 250-300 dollars. Hopefully you caught it early, otherwise you'll burn your torque converter.

Remember, his tranny is electronically controlled and if his valve body was shot, it would not go away if he shuts it off for 5 seconds and restarts it and it is gone.

This is definitely electrical or computer related.

Sorry for my last post I should have been more detailed. Unfortunatley I'm not a mechanic so I'll try to explain the best I can.

This problem usually occurs on warm days and after the tranny reaches a certain temp. The heat shrinks the valve body and pressure builds up kicking on your service engine light. P1870 code. If my blazer was shifting hard I would stop and restart the car and the hard shifting would disappear. The problem is in either your valve body. Have the tranny shop drill out your valve body before wasting more money on other fixes. i.e. solenoid. Thanks for your time.

Sorry for my last post I should have been more detailed. Unfortunatley I'm not a mechanic so I'll try to explain the best I can.

This problem usually occurs on warm days and after the tranny reaches a certain temp. The heat shrinks the valve body and pressure builds up kicking on your service engine light. P1870 code. If my blazer was shifting hard I would stop and restart the car and the hard shifting would disappear. The problem is in either your valve body. Have the tranny shop drill out your valve body before wasting more money on other fixes. i.e. solenoid. Thanks for your time.


I'm not very smart but explain exactly how heat "shrinks" a valve body. In my experience, heat causes most metal parts of a car to "expand". If you're not a mechanic (fortunately) , don't assume that just your diagnosis is the only one that is correct. Also, if you just "stop and restart" the car, at what point in there does the tranny cool off and allow the valve body to "shrink" or "expand" back to it's normal state where no pressure is built up during operation, allowing it to shift normally once again? :shakehead

I encourage anyone on this forum to do a search on the internet regarding hard shifting between 1st and 2nd gears. You will find several hits on this topic. Here is just one of thousands of posts you will find.

"I wish to impress upon owners of similar vehicles with the 4L60E automatic transmission that the problem originates in a faulty valve body causing hard shifting from first to second gear. The engine light comes on, and code P1870 will be rendered upon performing a diagnostic scan. At this point the friction material on the lock-up portion of the torque converter is mostly burnt away. Also, within the transmission body, the improperly hardened sun-shell gear teeth have begun to grind themselves smooth. This will now cost you a complete rebuild. Smile while GM and it's dealers denounce any knowledge of this common condition, as they suggest that the problem may lie within the driver and/or lack of maintenance. Otherwise, this is peppy luxury sport-utility that achieves acceptable fuel economy, gobbles the snow like candy, and starts in any weather thus far."

I'm speaking from experience. 2 years later after having my valve body fixed my blazer shitft great. Listen, in regards to the metal in the valve body. Once again, you will find thousands of posts on the internet dealing with the inferior metal in 4L60E transmission, and if you look hard enough you will find a service bullentin from GM.

I have done the research on this problem and I advise you to do the same.

I encourage anyone on this forum to do a search on the internet regarding hard shifting between 1st and 2nd gears. You will find several hits on this topic. Here is just one of thousands of posts you will find.

"I wish to impress upon owners of similar vehicles with the 4L60E automatic transmission that the problem originates in a faulty valve body causing hard shifting from first to second gear. The engine light comes on, and code P1870 will be rendered upon performing a diagnostic scan. At this point the friction material on the lock-up portion of the torque converter is mostly burnt away. Also, within the transmission body, the improperly hardened sun-shell gear teeth have begun to grind themselves smooth. This will now cost you a complete rebuild. Smile while GM and it's dealers denounce any knowledge of this common condition, as they suggest that the problem may lie within the driver and/or lack of maintenance. Otherwise, this is peppy luxury sport-utility that achieves acceptable fuel economy, gobbles the snow like candy, and starts in any weather thus far."

I'm speaking from experience. 2 years later after having my valve body fixed my blazer shitft great. Listen, in regards to the metal in the valve body. Once again, you will find thousands of posts on the internet dealing with the inferior metal in 4L60E transmission, and if you look hard enough you will find a service bullentin from GM.

I have done the research on this problem and I advise you to do the same.

Ok, again, this is not a friggin valve body problem so quit saying it is!

He says if he stops the truck, turns it off , then starts it right up again the problem is gone.

If it was a valve body, the problem would still be there seeing valve bodies don't fix themselves in 3 seconds.

Double Post, sorry.

Don't waste your time man. Some people can't comprehend some things.

One last post on this subject. Here is a post from a mechanic who has owned a tranny shop for over 20 years. In short, the problem is the valve body and TCC regulator which is included in a valve body kit. Once again, do some reserach Blazerlt before you post stuff that doesn't help anyone.

"This is a VERY common problem with the GM 4l60-E transmission. This is 9 times out 10 a VALVE BODY PROBLEM not a transmission problem. You need to pull the TCC regulator valve from the valve body & install a sonnax TCC regulator valve kit. DO NOT LET SOMEONE SELL YOU A TRANSMISSION UNTIL THIS UPDATE IS DONE FIRST!!!!!! This will more than likely take care of your problem. Also the reaso you get a hard 1-2 shift is when the P1870 code sets the computer commands max line pressure. I have had a transmissio shop for over 20 years & have only seen maybe 1 or 2 times the valve body update not take care of this problem.
Hope this helps you all out."
Thanks
Sean Ciciarelli

I guess im wasting my time trying to help a fellow poster with the same problem I had. I have provided helpful information and I have much more info regarding this problem if your interested Charlie.

Hope this helps.

I would have to agree that it sounds like the Ignition Switch when mine went bad i got the codes
P0758 solenoid B,
P0753 Solenoid A,
P0785 Shift timing solenoid,
P0740 Torque converter clutch,
P1860 Transfer case contact plate D.
I was told it was the Tranny but it turned out to be the switch. The carbon buildup on the contacts prevent power to certain componets.
I know of others with the same problem, some even paid big $$$ for a new tranny just to have the same problem until they replaced the switch.
By the way it was a person with a 2001 blazer who told me about the faulty switch but it seems to curse the 97's more often

Hate to say it, but this sounds like the ignition switch causing the problem.

It is a black module in the steering column.

Swap it out.

It is known to cause transmission problems, engine problems and the works.


i am having the exact same problem on my '97 blazer i just bought can someone tell me where this switch is located and what it is officially called and how much im looking at to replace it


thanks

UR2SLOW4ME2C@aol.com

here is one at advance
http://www.partsamerica.com/ProductDetail.aspx?mfrcode=GPS&mfrpartnumber=S193&parttype=410&ptset=A

If this truck is scanned with a trans capable scanner the power to the solenoids can be confirmed, shifts can be commanded and any slippage percentages will be seen, this will eliminate all the guess work involved, including the blame all ignition switch. Most p1870 conditions ,with no other codes, are traceable to the chronic valve body bore wear for the TCC valve.

If this truck is scanned with a trans capable scanner the power to the solenoids can be confirmed, shifts can be commanded and any slippage percentages will be seen, this will eliminate all the guess work involved, including the blame all ignition switch. Most p1870 conditions ,with no other codes, are traceable to the chronic valve body bore wear for the TCC valve.

Please do some research through the threads.

A lot of people with a phantom trans slip code have traced it to a 1997 ignition switch fault.

Please stop running around to all the ignition switch problems and confusing people. We have helped several people with this so don't just walk in and tell us all that we are wrong.

If it is a 1997, it is more than likely the faulty ignition switch and there is a TSB out on this to back us up.

thank you.

Listen, I never said you were wrong ,this is an issue of proper diagnostics not just put this switch in with no real diagnostics. My suggestion to scan was to confirm or deny the ignition switch as being the source of the problem. After having personally checked and repaired at least 10 p1870 only problems on both trucks and fwd GM vehicles, not one was an ignition switch problem they all were valve body issues, my comments are based solely on these experiences. I agree with you that the switches are problematic, but a stand alone p1870 with no other codes, driveability symptoms or loss of accessories is not an ignition switch problem.

I am just saying, on a 1997, most of these phantom problems are caused by the ignition switch.

I have seen the replacement fix the problem dozens of times.

I am only talking about the 1997. And a lot of people were told they had to rebuild their transmission and change the solenoids.

They took our advice, changed the switch and loe and behond, it fixed it.

thx.

P1870 isn't a code caused by the ignition switch. P1870 means that a slip has been detected. P1870 indicates a mechanical problem not an electrical problem. The most common cause of a P1870 code is the valve body. The hard 1-2 shift that occurs is a result of the code being set and the PCM commanding maximum line pressure. When the igniton is turned off the hard shift stops until the slip is detected again.

An ignition switch malfunction would set one or more of the following codes:
P0740
P0753
P0758
P0785
P1860
It is often accompanied by gauge malfunctions and if any of those codes are set the transmission will go into limp mode and lock into 3rd gear.

My mistake, I though this was a 1997 application.

I apologise.

The guy that brought this thread back up in post #15, just said that he had a 97 with the same problem. Two completely different problems have been discussed here, I was just telling the difference between the two. His problem may be either one, but with the common faiures of the 97 ignition switches, I would **GUESS** that to be his problem. However, it shouldn't be assumed that either is the cause without more information.

Code P1870 is one mean dude code. And the newer the vechicle the meaner it gets.
Kinda makes you want to run out the back door when one comes in the front door.
You have to do your home work and a lot of testing to get to the root cause.
MT-2500

had same prob with our 99 ,, it was indeed the valve body, tcc pwm solenoid

I guess we can put the ignition switch issue to sleep now, relative to this trans problem.

Right on there Maxwedge
Keep up the good work.
And have no fear Crunch is here.
MT-2500

i guess the cause may be several things, mine just happened to be the ignition switch, It has been over a year since i replaced it and it hasn't been a problem since. I only know from experience. this is an issue with 97 blazer's, not to sure if other year models are affected

i guess the cause may be several things, mine just happened to be the ignition switch, It has been over a year since i replaced it and it hasn't been a problem since. I only know from experience. this is an issue with 97 blazer's, not to sure if other year models are affected

Yea, I remeber that, thanks for touching base with us and letting us know that the fix held out for you.

i am having the exact same problem on my '97 blazer i just bought can someone tell me where this switch is located and what it is officially called and how much im looking at to replace it


thanks

UR2SLOW4ME2C@aol.com

There is a thread on this, search for ignition switch and you will find it.

Just wanted to post since this thread helped me. I have a 2002 Suburban that began to idle poorly, dash gauges would work intermittantly, and it would drive like the parking brake was on. I scanned it and received these codes:

P0740
P0785
P1860

I eventually took it to the local Chevy dealer, they replaced the ignition switch. When I had them show me the old wire bundle - the mechanic told me that the root cuase was the aftermarket alarm that was installed (there when I bought it). An amateur installation, they had tapped into the ignition bundle in several places. This did not allow for the proper electrical charge to reach the Tranny valves listed above in the error codes that I received. I went ahead and let them change it, no problems since. Total damage for the ignition switch/bundle and install was $432 for parts and labor. ($157parts/$276/labor).

The dealer part number is 26098764 for the ignition switch, that is what is on the invoice.


HTH!

I have a 97 and had all these problems guys. I leaning towards the ignition switch. truck stalled and was throwing tranny codes. ignition switich is in the steering colum 70 bucks at advaced auto. took care of my rig know have 150K and runs shifts better than the day I bought it with 30k

jkdon

guys this thread is more that a year old. please refrain from posting in older threads in the future.