Verify the Systems Before Condemning the Transmission

Randy Peterson - Diagnostician

Diagnostician - Randy Peterson Randy has worked for Certified Transmission for over twenty four years and is an ASE Certified Master Technician, including L-1. He has been in the automotive industry for over 30 years.

A few months ago a customer brought in a 2003 Dodge 1500 Pickup with a 5.7 Hemi and 545RFE transmission. The check Engine lamp was on and the truck would not accelerate from a stop unless you put the transmission in second gear. I started the preliminary check procedure by checking the fluid. It was full, not in great shape but no burnt odor. Next, I scanned for diagnostic trouble codes. The ECM stored a couple EVAP codes and the TCM had a P2706 - MS (multi-select) Solenoid Circuit. Oddly enough it did not have a P0700 (Trans Control System Malfunction) stored in the ECM. This vehicle utilizes an ECM and separate TCM. After a short road test the customer's concerns were confirmed. I cleared the DTC and road tested it again to see if the code reset and it did. Further diagnostics were required. The vehicle owner authorized the diagnostics, and we began the process.

The first test I performed was on the electrical systems. This included testing the battery and verifying that the starting system and the charging system were operating correctly. Free State fully charged battery voltage should be around 12.6v. 12.4v is already considered 25% discharged. Cranking voltage should never drop below 9.6v and good running voltage usually ranges around 14v. It amazes me how many times this step is over looked in the diagnostic procedure. Low voltage, poor grounds, faulty alternators can wreak havoc on electrical components. You want to be sure if you find problem electrical components, a bad battery or faulty alternator does not cause the new replacement components to fail again. Thanks to Vince Fischelli for teaching me that.

Next, I printed off a wiring diagram and the published diagnostic procedure. I studied the diagram, gathered solenoid specifications and determined my next point of attack.

The TCM is the 60-pin type, similar to the ones used on the 604's and 42LE's. I located the TCM and harness, identified the pin(s) I wanted to check and started with (Multi-Select Solenoid Control) pin 40. I performed a simple Ohms test to see if there was an open from the TCM to the solenoid. There was no open. I needed to verify my findings so I tested all the solenoids. They all tested the same. We all know that an Ohms test is no indication of a good working system, so I load tested the solenoids and measured the amperage while activated. This tells me if the solenoid is working and if it continues to work once it gets hot. I was not able to use bi-directional functions because the TCM would go into fail-safe and shut the relay off. With the TCM disconnected I ran fused power to the connector. With this system, the solenoids are grounded and the TCM supplies power. I was able to determine that from the wire diagram. I powered pins: 19, 20, 40, 55, 59, and 60. All of the solenoids were 6.5 amps, including the MS solenoid. That is within the normal operating range. I ran the test again with the same results. My conclusion was a faulty TCM. I reconnected the TCM and road tested the unit. The code returned and it went to Limp Mode.

We recommended a TCM replacement and an ECM re-flash. The owner declined and took the vehicle. Who knew testing all of the solenoids at this time would pay off at a later date? The story does not end here.

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The owner took the vehicle to the local Dodge dealer for their opinion. I can understand a second opinion when there is a large cost involved. The dealer advised that the solenoid was bad and needed to be replaced. This repair was about half the amount we had estimated, but remember they were doing something completely different than what we recommended. The owner liked their price and authorized the repairs. Needless to say, it did not fix the problem. The dealer then told them "it must have a bad transmission then". The owner left the dealer $450 poorer and the vehicle was still doing the same thing.

The owner heeded the advice of the dealer, bought a carry-out transmission from our company, and installed it himself. Shortly after the installation we received a call stating our transmission does not work and we need to fix it. The vehicle was brought in and I scanned it for trouble codes. A few months had passed since the vehicle was last here and I did not recognize it at first. It had a DTC P2706 stored just as before. Again, there was no P0700 stored in the ECM. Just to be sure, I ran the diagnostic test again. My conclusion was the same, a faulty TCM.

The owner purchased a TCM from the dealer that recommended the transmission exchange. I'm not sure how that discussion went, but he proceeded to install it in our parking lot after hours. The next morning I was to check the installation and perform any pre-road test functions. I started my road test satisfied the vehicle would be fixed. When I started to take off, the Check Engine lamp came on and it was again in Limp Mode. I was shocked to say the least. What happened? I checked the codes, no P2706. This time P0750: L/R Solenoid Circuit Error and still no P0700 stored in the ECM. I knew from my previous test all of the solenoids were good. I was so familiar with the test I did it again. I concluded that the solenoids were good. The replacement TCM must be bad. I called the dealer and they supplied the owner with a warranty replacement. The owner installed the TCM. I performed the pre-road test functions and drove the vehicle. Yahtzee! It works, and it worked great.

I felt very comfortable that my diagnostic procedure was correct. It verified all of the working circuits under load. It also verified the support systems; battery and charging system were in good working condition and not contributing to the failure. I tested ALL of the solenoids, not just the one in question. That would help me later on when faults kept reoccurring and it provided a good comparison of the solenoids.

Why are parts replaced without proper diagnosis?

Is there a lack of knowledge or carelessness?

Do technicians not understand the circuits and how they work?

There are outstanding training programs out there but you have to take the classes and then practice what you have learned.

We charge for diagnostic time. It's an important process for your companies' creditability and it doesn't waste the customer's money with unnecessary parts replacement.