Extended Diagnosis Results in Complete Repair

Chris Adams - Diagnostician

Diagnostician - Chris Adams Chris Adams started with Certified Transmission in 1986 as an R&R technician, and currently works as our Diagnostic Trainer. His current duties involve training and advising our retail diagnosticians, as well as assisting in the research and development of our remanufactured products. He also holds ASE Master and L1 certifications.

A while back one of our retail locations received a 2011 Dodge Ram 2500 equipped with the 545RFE transmission and the 5.7L engine. The customer's concern was a neutral condition in higher gears. He also stated that the transmission has had shifting issues for some time but did not elaborate on what those issues were.

As I began the verification and diagnostic process, the first thing I noticed were severely corroded battery terminals, and this was going to need to be addressed. Fluid was full and burnt. Scanning the truck for codes revealed P0734 and P0735. Bothe were gear ratio error codes for 4th and 5th gears, respectively. While on the road test the vehicle did exhibit a neutral condition on the 3-4 shift command, but not surprising given the DTCs that were stored along with the customer complaint. I suspected the accumulator plate was the culprit, so I performed a pan inspection and verified that it was indeed the cause of the failure. The pan and filter were also full of debris. This unit was done.

The diagnosis was straight forward, and I knew the cause of failure and what we needed to do to get this Ram back on the road. The customer was given the repair timeframe and cost of repair to install a remanufactured transmission, clean the battery terminals, and flush the cooler with the Hot Flush machine. The customer approved the repairs and we proceeded with the transmission replacement.

The work was completed without any other additions to the repair, so it was handed back to me for a final drive and recheck. On the road test everything was working well up until I did a forced 3-2 downshift. There was an apparent delay and then bang! The transmission slammed into 2nd gear. I tried this a few times with the same results. I had performed a "Quick Learn" before I started the road test and observed the CVIs, but nothing seemed to be out of line, so I returned to the shop and started the QL procedure again for good measure. I went out for another drive with the same results; a really hard forced 3-2. More diagnosis needed to be done.

Most anyone that builds these units regularly knows that there are some issues with some valves in the VB and pump that need to be addressed at the time of the build. In our facility we utilize Sonnax™ vacuum testing stations and we rarely see any valve body issues after we are done with these units. So where do we go from here? It seemed the issue had to be in the valve body, right? Well, that is the road I went down with no looking back.

I ordered a replacement valve body from our warehouse and installed it. Unfortunately, I was left with same problem: hard forced 3-2 downshifts. I then drove the vehicle with the scan tool connected, monitored the PIDS, and made recordings. I could not see anything that I could take issue with, so it was evident that the remaining diagnosis wasn't going to be basic. It was time to get serious and break out the lab scope and hope that I could see something irregular to send me down the right path to correct.

Since there were five solenoids that I wanted to look at initially, I needed to use our scope capable of displaying ten channels. My initial setup on this was to look at the low/reverse, underdrive, multi-select, 2C and 4C solenoids. I did not connect to the line pressure solenoid as the pressures all looked good from the initial scan data I looked at before we got here. The problem always seemed to be worse when the truck was hot, so I had let it run for a while before we went off to record data with the scope. This scope is capable of recording data, so rather than trying to look at it live I simply triggered a recording as the problem reared its ugly head and went back to review.

This is a screenshot of what I saw while reviewing the data. The top section is a complete recording, and the bottom is zoomed in view of what is between the two cursors. (Figure 1)

Article Figure 1

Figure 1

Neither the multi-select nor the 2C solenoid patterns looked correct. I had my suspicions, but I had already acted on a hunch once on this issue and didn't want to make that mistake again. To confirm my thought, after checking every wire going to the transmission from the PCM for any type of short-to-ground or short to another wire, and then load-testing all the solenoid control wires, everything checked fine there and was eliminated as a cause. I was down to replacing the suspect PCM, so I ordered a new one from our local dealer. It was going to be four or five days before the new PCM showed up, so in the meantime I reconnected the scope up so I could look at a few more items. I was not in a time-crunch at this point and more data is always better, right? I added the Pico pressure transducer, line-pressure, and overdrive solenoids to the mix for observation.

Remember when the customer said that the transmission had been having shifting issues for some time before the failure happened? Well, when we called him and explained what was going on and why we now needed a PCM, the customer explained what those "shifting issues" were, which was a bang when slowing then accelerating! Maybe if I would have known that from the beginning, I could have saved a step, but I was the one jumped to replacing the VB and I must own that.

I installed the new PCM and programmed it with the latest calibration (the original had already been updated to the latest), and I had the scope all set up again and ready for another road test. The transmission performed perfectly with no delay, no bang on the 3-2, and all of the shifts were good.

Here is a screen capture showing the recording after the PCM was replaced. (Figure 2)

Article Figure 2

Figure 2

The sample rate was the same at 10us (10 microseconds), but I did have to change the "ms per division" due to adding channels and recording time. Because of this, the patterns look just a bit differently, but I think it is clear just by comparing the two patterns that the issues were corrected with the PCM replacement.

In the end, some extended diagnosis was required in order to completely resolve all issues. The takeaway is that simply repairing the obvious does not always fix the root cause. Drilling it down through the process of elimination resulted in a complete repair and a happy customer.