2000 Century Harsh Shifting when warm

[bignoisey]

Problem is intermittant. All OK when cold. After a few miles of warm up the transmission starts making a buzzing noise which increases in pitch with engine speed then all gears shift harshly. Its been getting worse lately. It was rebuilt a year ago due to a failed torrington bearing. Several gears and other stuff was replaced, metal pieces found in the pan. Took it to the tranny shop that did the rebuild. They saw a trouble code P1811 which they can't be sure is the cause of the problem. I've tried to determine what this code means but it's not listed in any documentation I found. They want to tear it down again and that will cost me a bunch. I hate to let them do that when they are unsure of what the intermittant problem really is. I'm afraid they'll fix everything but the problem. Anybody seen this problem in a 2000 Century or other 2000 FWD GM car?

[RABarrett]

If someone could assist in the definition of the code, I can assist w/ troubleshooting. W/ respect to the noise, two things come to mind. The first, and most likely, is a plugged trans filter. The restriction may be causing the pump to cavitate, affecting directly the shift quality due to low pressures. This situation could also cause the 1811 code if it relates to a vague powertrain code. Vague codes include such things as random misfire. If the trans intermittently slips, vague codes such as random slippage may be set. The other possibility is the pump or pressure regulator valve may be intermittently affecting fluid pressures, causing the same problems. Ray

[bignoisey]

Thanks for the offer Ray. I forgot one piece of info, I just had the fluid/filter changed in that tranny shop that did the rebuild a year ago. That was the first (and cheapest) thing to try. One thing which agrees with what you said is that shop manager also thought it may be that the pump or regulator is Flakey when warm. I hate to shell out about $1000 minimum for a R&R and teardown when the problem is so undefined. I'd also have to rent a car for 2-3 days. I'll keep looking for the definition of the P1811 code. One other thing that comes to mind was that a Bearing disintegrated causing the first rebuild. Do you think some fragment could still be circulating somewhere through the passages causing this? If so, then why do I have the problem only when its warmed up?
-- Paul

[RABarrett]

Some things to remember is that the fluid viscosity drops as temperature rises. This in itself will change fluid pressures. The other thing to remember is that internal clearances will change with the same temperature rise. It is quite possible for the Torrington's demise to have left debris in the transmission. Question: Is the noise constant w/rpm or does it change with shifting? Is the noise different when the trans is in third than when in reverse or overdrive? Something else to consider is the possibility that the valve body is not seating correctly with the housing, causing internal leaks, and pressure loss. Maybe this shop would check the bolts on the valve body as a goodwill gesture? More food for thought. Ray

[comp]

i've seen loose valve body's on all make's

[lanierboy]

I have a 2000 Century and it does the same thing. It started at about 70k miles. It will run for a while and then start whining and shifting hard. If I turn off the motor and start again, it will quit ... at least for a while. It appears to happen sooner on hot days and in heavy traffic. The only thing I've done to the transmission is change the fluid at about 60k when I purchased the car.

[bignoisey]

To answwer Ray's question the Noise (whine, or buzz) increases with engine RPM. Its the same in any gear or neutral. But as Lanierboy describes, it runs for a while fine, then all the symptoms start up. Yes I can shut it off and it ceases for a little while, then comes back. Just lately, and just before the symptoms are solid, it seems to jerk between gears when starting out in 1st, when the whine and hard shifting appears this behavior goes away.
I think I got a definition on the P1811 trouble code
DTC P1811 Maximum Adapt and Long Shift
This code does not turn on the SES Light
This comes from the web site http://pcm.dxsoftware.com/dtcs.htm
Which looks like a good resourfce for these.
Anybody got an idea what this means?

[RABarrett]

If this code definition is correctly defined, it marns that the shift for which the code is set is too long for the clock in the computer. Essentially, it means that during the time the computer is preprogrammed to delay timing advance, the sensors on the input shaft of the trans and the output shaft should reflect the ratio of the gearset and the output shaft. That means that, if the trans is supposed to upshift from second to drive, the ratio between the output shaft and the input shaft should be essentially the same, if the torque convertor is engaged. The computer knows the torque convertor status since it established it. If, during a normal shift, which should take about a 1/2 to one second, the time frame established by the software, is exceeded, the code is set. This code essentially indicates either slippage in the trans or a slow upshift. Both are indicative of fluid pressure problems, or problems with the clutches controlling the planetary. Ray

[bignoisey]

Interesting definition. When the car is having the problem, the shifts between all gears is very quick and abrupt - not like slipping. But I do feel a shudder on the 1-2 shift when I don't have the problem (cold) under fairly heavy acceleration. Now I'm really confused. Maybe the code is saved from some time long ago.

[RABarrett]

If the shudder is confusing the PCM by allowing an extended shift, or slippage, the result may appear to be an extended shift. It might be wise to have the code cleared and then evaluate the trans' operation. If the SES light is not illuminating , the code is not a fresh one. The code is only fresh if the light intermittently illuminates, and that is the only code set. Ray

[Flatrater]

GM has a bullentin on this condition the repair is to replace the PCS solenoid inside the trans.

Slips, Harsh Upshift or Garage Shifts, Launch Shudders, Flares, Erratic Shifts and Intermittent Concerns, DTC P1811 or P0748 Set (Replace Pressure Control Solenoid Valve Assembly) #00-07-30-002B - (07/19/2002)

Here is what a shift adapt is!!
Adapt Function
The 4T65-E transmission uses a line pressure control system, that has the ability to adapt line pressure to compensate for normal wear of the following parts:

The clutch fiber plates
The springs and seals
The apply bands
The PCM maintains information for the following transmission adaptive systems:

Upshift Adapts (1-2, 2-3 and 3-4)
The PCM monitors the automatic transmission input shaft speed (AT ISS) sensor and the vehicle speed sensor (VSS) in order to determine when an upshift has started and completed. The PCM measures the time for the upshift. If the upshift time is longer than a calibrated value, then the PCM will adjust the current to the pressure control (PC) solenoid valve to increase the line pressure for the next shift in the same torque range. If the upshift time is shorter than the calibrated value, then the PCM will decrease the line pressure for the next shift in the same torque range.

Steady State Adapts
The PCM monitors the AT ISS sensor and the VSS after an upshift in order to determine the amount of clutch slippage. If excessive slippage is detected, then the PCM will adjust the current to the PC solenoid valve in order to increase the line pressure to maintain the proper gear ratio for the commanded gear.

The TAP information is divided into 13 units, called cells. The cells are numbered 4 through 16. Each cell represents a given torque range. TAP cell 4 is the lowest adaptable torque range and TAP cell 16 is the highest adaptable torque range. It is normal for TAP cell values to display zero or negative numbers. This indicates that the PCM has adjusted line pressure at or below the calibrated base pressure.

Clearing Transmission Adaptive Pressure (TAP)
Updating TAP information is a learning function of the PCM designed to maintain acceptable shift times. It is not recommended that TAP information be reset unless one of the following repairs has been made:

Transmission overhaul or replacement
Repair or replacement of an apply or release component (clutch, band, piston, servo)
Repair or replacement of a component or assembly which directly affects line pressure
Resetting the TAP values using a scan tool will erase all learned values in all cells. As a result, the PCM will need to relearn TAP values. Transmission performance may be affected as new TAPs are learned. The PCM must also relearn TAP values when the PCM or the transmission is replaced.


Bascily what this says is the PCM is a learning PCm it learns the drivers habits and learns the wear of the trans over time and uses this info to change the shift points to be less noticable.

After any trans repairs the shift adapts have to be cleared and relearned.

[Flatrater]

Here is alittle info about your code of P1811!

Circuit Description
The transmission pressure is modified by an adaptive modifier which controls the shift execution time. This test checks the time required to accomplish the shift. If the shift takes longer than 0.65 seconds and the adaptive modifier cannot shorten this time, then a counter increases by one.

If the PCM detects a counter value of 2 during one trip, then DTC P1811 sets. DTC P1811 is a type C DTC.

Conditions for Running the DTC
The shift is adaptable.
The 1-2, the 2-3 or the 3-4 shift adapt cell has reached its limit.
Conditions for Setting the DTC
The 1-2, 2-3 or 3-4 shift is longer than 0.65 seconds, twice in one trip.

Action Taken When the DTC Sets
The PCM does not illuminate the malfunction indicator lamp (MIL).
The PCM commands maximum line pressure.
The PCM freezes shift adapts.
The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Failure Records.
The PCM stores DTC P1811 in PCM history.
Conditions for Clearing the DTC
A scan tool can clear the DTC.
The PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission-related diagnostic fault occurring.
The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.
Diagnostic Aids
Ask the customer about possible overloading, exceeding the trailer towing limit, or towing in overdrive.
Ensure that the PCM has the latest calibration update.

[bignoisey]

Wow! thats a lot of good information, Flatrater . I suppose replacing the PCS solenoid is not something I can do in my own garage. I think I understand a little more now. I'm going to provide this to my Tranny guy so he'll understand. Thanks.

[Flatrater]

No the PCS is no an easy job it requries you to remove the trans side cover and then you need a scanner to clear shift adapts. Clearing the TAPS is the most important part of the job.

GM has a problem with the PCS solenoids they are made of a softer metal than the hole they ride in after a while they wear and start hanging up.

[lanierboy]

Flatrater, thanks for the great information. This is something I'll attempt in the near future.

To clear the taps. Will a regular ODBII scan tool work or do I need something special.