99GTP: Transmission slipping, TCS Off, and multiple codes

[DrRadar]

The trans recently started slipping...at least, that's what I think is happening. Low speed/gears seems fine. When accelerating at, say 40 mph or more, it sometimes "surges" or "shudders", like it's trying to accelerate then gives up, tries again. Happens often on entrance ramps. Not too objectionable yet - still can get around - but it's not right and bound to only get worse.

About the same, I noticed that TCS Off was always lit. No CEL/SES or ABS warning lights. The local parts store used a Bosch 1300 scanner to read these codes: C0244, P1111, P1689, P1811. I don't know if all these codes are related and, if so, what is root cause - ABS/TCS (EBTCM) failure causing the "slipping" or "shudder" or an aging transmission causing a TCS problem.

The weekend prior to these problems, I replaced by a/c compressor, accumulator, and orifice. So I had the ABS modulator disconnected from master cylinder and out of the vehicle. I didn't have a problem with a firm brake pedal when re-installed so don't think there's air in the ABS modulator. The PCM was also removed to access the accumulator. Don't know if this is significant.

P1111 (Intake Air Temperature Sensor Circuit Intermittent High Voltage) appears to be unrelated to the others and a problem with that circuit. I don't know the consequences of a faulty sensor but I'm inclined to think it's minor and to ignore this code for now.

P1811 (Maximum Adaptive Long Shift) likely indicates transmission wear - correct? The trans has 207k on it. Regular fluid/filter changes and some Lucas additive but no other maintenance, no past problems.

P1689 (TCS Delivered Torque Control Circuit) It appears that this indicates that the PCM is not sensing 12V from EBTCM onto which the PCM can modulate the output torque signal. Anything to do with the transmission? Suspect EBTCM or wiring?

C0244 (PWM Delivered Torque Malfunction) Not sure what to make of this code. Lots of cases where wheel bearing hubs replaced because of bad ABS sensors (which I've never done - original hubs) but is this a casualty of a failing transmission?

Any guidance is appreciated.

[richtazz]

The P1111 is unrelated to your trans issues. It will affect short and long term fuel trims, but not the trans.

The other 3 are trans codes, indicating possible wear especially at your mileage, but possibly just bad shift, tcc, and pcs solenoids (common issues on these cars at high mileage). IF your trans fluid is still red/pink, and there is no metallic flake in it, a side cover removal and solenoid replacement may fix it.

[DrRadar]

Thanks for the reply, Rich.

The fluid was changed 10k miles ago. Should still be red.

I've been reading other posts on how to fix this problem. From seafoam, filter, and shift kits (seems easy enough) to replacing PCS (seems like a lot of work).

I'm foolishly attached to this car. Inspired by tales of GTPs getting 300k - 400k, two years ago I started a top end rebuild and ended up pulling the engine for a complete rebuild. And I didn't go the cheap route in having the block and heads rebuilt. Considering the 208k miles on the transaxle and only 10k miles on the rebuilt engine, I'm leaning toward getting the transaxle rebuilt by a local shop in the hope of getting another 100k (or more) out of it. Seems the other fixes wouldn't get me that far.

Am I kidding myself about longevity of a rebuilt transaxle?

[DrRadar]

Had transmission rebuilt. TCS is now working normally. No slipping.