Recently a customer called to get a quote for a 1998 Ford F-150 4X4 with the 4.6L engine and 4R70W transmission. The price was given and we had one in stock. A couple of days later they called and told us they needed the transmission. It was still in stock, but late in the day so arrangements were made to get it delivered to them the next day.
The next day we received a call from the shop that there was a problem. Like fingernails on a chalkboard we cringe. “This transmission is doing the same thing as the old one.” What we have to remember is this is a cry for help. They have a problem and don't know how to proceed. Time to get the vehicle to our shop and put on the diagnostician hat.
Communication becomes critical at this point. We need to know symptoms and codes that were present before they started working on the truck. I knew the old transmission was toast based on the fluid color and condition. However if there is still an issue that told me the transmission was a victim not the culprit.
Arrangements were made to get the truck towed to our shop. The timing worked out great. I had just finished a final road test when it arrived, so I was able to get right on it. We take warranty issues very serious, they take top priority.
I grabbed the paper work & scanner and headed out to solve the mystery. The other shop did not have any information other than the truck barely moved when they got it, so no history of codes. When I plugged the scanner in I retrieved several codes, all of which were solenoid codes. We know this typically means no power to the transmission. Trying to keep it simple I first checked fuses, all okay. Next I went to the transmission and checked the connector. It was plugged in properly, no pins pushed out, no green fuzz. However, there was no power on pin #4 (red wire) confirming my suspensions. Now let’s go to the other end. I checked for proper voltage going to the PCM at pins #71 and #37. These were both okay. Next quick check of pin #87 that supplies power to the transmission, it was okay. Now we have the answer, its a bad wire from the PCM to the transmission. We placed a call to the shop explaining what we had found and to get the okay for further testing and repairs since this was obviously not a warranty issue. They authorized us to find the problem and fix it.
Back at the harness I wanted to check all the wiring going from the PCM to the transmission. Do we need to just run a new power wire or is there more? Guess what? No reading on multiple wires. So we either have a smashed or damage harness. Let’s look. Can't see a darn thing, no room. I went below and disconnected everything and removed the harness from above. A plastic retaining clip had broken and allowed the harness to contact the exhaust. We found a silver dollar area that was now one melted together glob. A short time later after splicing and repairing the wires with connectors, solder, and heat shrink we were all back together. Now to stuff the harness back in without the truck eating my hands.
Back in the seat of the truck, scanner plugged in and voila no codes. I headed out on the road for a comprehensive road test. The transmission shifts great, good TCC. About 20 minutes later I returned to the shop and raised the truck one last time to check for leaks and to make sure the harness was in place. The shop was then called to let them know truck was done and ready to go.
A sense of calm and relief returned and everything was right in the world again.
We have seen this type of issue several times since. It saves a lot of time and grief to really pay attention when doing a checkout. Fluids nasty burnt, slips in the parking lot, yes it will need the transmission replace but just a few minutes to check for codes and hmmm? We may have another issue. Also the harness repair would have taken a lot less time when the transmission was out of the truck. We also need to remember when we get the call “It’s doing the same thing” what they are doing is telling us there is more than one problem and they need our help
On the subject of the 4R70W, We had a local police car come into the shop with a "failsafe" condition. Initially it had a laundry list of codes stored in the pcm. After clearing the codes and driving the vehicle was still in failsafe with codes for the PCS and Shift solenoid B. After replaceing a blown fuse twice i decided to see what was on that fuse circuit. Come to find out the oxygen sensor and a few others were on the same power circuit at the trans solenoids. Upon further inspection I found a damaged oxygen sensor, replace it and problem solved. Lesson: Not all transmission concerns are directly related to the unit itself. As I have come to find over the years, many manufacturers pile other components onto the trans circuits. Great idea...NOT!!!
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