Emissions Test Failure

My friend has a 2003 Grand Prix. Took it for emiissions test. They told her the "torque converter clutch circuit" is stuck on. What the heck is that, and is it expensive to repair?

It could be expensive if it requires removing the transaxle side cover or rebuilding it. Do you have the specific code (DTC)? What it means is the torque converter clutch is possibly stuck to the on position and not turning off when commanded to do so. The TCC is supposed to cycle on and off depending on the driving conditions and what gear the car is in.

Yes, they did give a DTC code : PO742.

In order to set the P0742 DTC the PCM module has detected that the TCC release switch is closed when the TCC is commanded off meaning it has detected it is actually stuck on or open. The TCC release switch is part of the automatic transmission fluid pressure manual valve position switch (TFP) which is located on the valve body.

So the first step is to check ATF level. Next step with engine off is to remove the 20 way electrical connector at the transaxle and reseat it. Next step if the transaxle hasn't been serviced recently is do a pan drop service and replace the ATF and screen filter. After that major transmission service will be required.

Thanks BNaylor! I'll let you know what the outcome is soon. Thanks again!