hi Everyone, I seem to have an intermittent problem with my 98xk8 transmission that is baffling a few people. Wondering if anyone out there has had the same problem and hopefully has a fix for it.
When I'm accelerating from a standstill the car pulls away as normal and seems fine. however if I back off on the throttle before it gets into 3rd gear then it stays in second and the engine gives me braking as if i was holding it in 2nd gear manually. if I continue accelerating it changes up normally. Seems to occur more on hills (up or down), does not happen so much if car is in sport mode.
This has been happening for a while now, recently the front clutch drum broke and the trans was removed and reconditioned,( at great expense) I told the rebuilder of this problem and he seemed to think that it would go away with a rebuild, needless to say it hasn't.
I have disconnected the battery to reset the computer and the problem goes away for a short time only to return a day or so later.
have checked all connections etc , computer fan is working. I get no fault codes or messages. Can anyone give me any ideas where to look next please?

 

The transmission control module (TCM) controls shifting via an electrical cable to the left rear of the transmission connected to control valves. Easiest task is unplugging the connector looking for a bad connection. Since that was done with the transmission removal/installation that probably leaves the valves and the TCM. I had a bad TCM that would not release the torque converter lockup on downshifts. Like you, learned to drive around the issue because I refused to buy a $2000 TCM until I saw the failure on an Auto Enginuity Scan Tool. Found one in a wreaking yard for less than $100.

Guess what I am saying is that you probably have a sticky electrically operated valve or a TCM failure.

 

Have your transmission fluid checked to see if the transmission needs any fluid. We had our transmission rebuilt and the rebuilder filled it with fluid before they tested it on their dyno. Our mechanic only added another 1 liter bottle of fluid after he installed the transmission. We had a problem a week later and the transmission gave us the gearbox fault and went into limp mode. I called the rebuilder about the problem and I was told to have our mechanic check to see if the transmission is fully filled with fluid. The transmission needed another one half 1 liter bottle to fill it. There were no record of any faults in the TCM or the ECM. We have not had any problems with the transmission from then on.

 

To jimlombardi, thanks for the input, I know for sure that the right amount of fluid is in the trans so don't think that is the issue.
To test point, again thanks for replying I had a feeling that the TCM may be at fault as the problem clears temporarily when the tcm is reset. I have just located one in a wreckers yard , apparently it is from a 2000 car and the wrecker says it will fit, would you know if he is right and will I damage my car trying it if he isn't ? . Appreciate your help. Jimmy1

 

The part number PLUS the 3 digit (/xxx) extension must match. Otherwise it is plug and play. The extension designates all the matched components on the CAN buss. Look in the spare tire area for a label with all the CAN connected modules part numbers and extensions. A different one may not work properly but should not permanently harm the system if you must try it.

Be sure to disconnect your battery before removing the old one and installing the new one.

 

To Test Point, thanks for that info, I have located the necessary numbers in the spare well and I am going to try the TCM tomorrow so hopefully all will be well. The guy at the wreckers is kindly allowing me to "try before I buy" so I will let you know how things pan out. At least I'll be able to eliminate the TCM from my list if it doesn't get better.
Thanks again. Jimmy1

 

To Test Point, I have installed the second hand TCM and my troubles are over. I think that the problem was similar to yours in that the Torque converter lock was not always releasing when backing off on the throttle. Thanks again for your help it's great to get a result at last! Jimmy 1.