By Jerry Huerter, Diagnostician
Jerry is a Diagnostician at Certified’s Overland Park KS location. He is an ASE Master Certified L1 technician and has been with Certified for over 5 years with many years of automotive repair experience prior to joining our team.
When a vehicle comes into your shop for repair you need to determine if you have access to service information, the equipment needed to make the repair, and if you have the experience to repair it. As you read this article you will see just how challenging a transmission replacement sometimes can be. In this particular situation the service information was misleading and special equipment was needed to make the repair. This was one job that turned into yet another learning experience for me.
A 2007 Dodge Caliber with a CVT transmission came into our shop. It previously had been at another shop where they had replaced the transmission with a used unit. The customer stated that after the transmission had been replaced with the used unit it seemed to slip and the check engine light came on. When I scanned the TCM I found a P0843 secondary oil pressure sensor circuit high, P0741 torque converter clutch circuit performance and P167A calibration mismatch. After clearing the codes I took the vehicle for a test drive. The transmission seemed to work okay, but the engine RPM’s seemed a little higher than normal. The P167A code reset as soon as the ignition was turned on and the P0741 code reset during the short test drive. The P0843 code did not reset.
Service information stated that this CVT uses the torque converter for launch only, then locks the converter up at around 12 mph. The P0741 code sets when the TCM detects excessive TCC slip for 30 seconds and it takes 2 failures to set the code. This explains why the RPM’s were higher than normal but the question is, what is the cause of the TCC not locking up? The P167A calibration mismatch code will set when the information in the TCM does not match the information in the Rom chip which is located inside the transmission. I decided the P176A should be diagnosed first. The service information states that a relearn procedure needs to be performed on the TCM. I searched and found service bulletin #18-019-06 that states if check engine light on and DTC’s P0602, P167A, or P161B are present both controllers (TCM and PCM) must be reprogrammed.
The TCM reflash was successful but the ECM reflash failed. The electronic throttle is now limited to around 6 percent, which is just above idle, and the vehicle is no longer drivable. I used a J2534-1 programmer, which is an early model. Since this was a CAN vehicle I suspected that the programmer I had used was the reason for the reflash failure. My son Ryan, who operates a reflash business, brought his J2534-2 programmer over. His programmer flashed both the TCM and PCM successfully.
Upon starting the vehicle there was no check engine light on and no P167A code set. I then took the vehicle for a second test drive. The electronic throttle now worked, the TCC locked up and the RPM’s returned to normal. Everything seemed to be working properly. I shut the vehicle off and restarted it only to find that the check engine light was back on, the P167A code had set again and the electronic throttle went back to not working. So it was back to the drawing board!
After more research it looked like the factory scan tool was the only way that the TCM could be relearned to accept a different ROM chip after a transmission replacement. I also found that some technicians are installing the original ROM chip in the replacement transmission. This chipset was programmed when the transmission was assembled and carries vital information on the variators and hydraulic system. The ROM should never be interchanged with any other CVT. It is unique to the CVT it came with. Now the vehicle needed to be taken to the dealer to be relearned, but it couldn’t be driven because the electronic throttle control was restricting the throttle. Rather than having to tow the vehicle to the dealer I was able to locate a mobile trouble shooting company who came to my location. Using their factory scan tool they were able to relearn the TCM. After this procedure the operation of the CVT transmission returned to normal.