- Subject: No electrical power to transmission
- Unit: 4R70W
- Vehicle Application: Ford F-150 4X4
- Essential Reading: Rebuilder, Diagnostician
- Author: Carman Klaber
Paying close attention during diagnostic check can save time and trouble
A wholesale carryout transmission can be a great addition to your weekly sales. We try to assist our customers by sharing our years of troubleshooting experience. Since we specialize in transmissions we have more opportunity to learn from the school of hard knocks.
Recently a customer called to get a quote for a 1998 Ford F-150 4X4 with the 4.6-liter V-8 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 it was late in the day so we made arrangements to deliver it to them the next day.
The technicians in our shops jump in and do whatever is necessary. This can be from diagnosing a complex electrical issue to dumping the trash, so first thing in the morning I loaded the transmission to deliver it. The shop was just finishing removing it from the truck. I greeted everyone and together we unloaded the transmission. I checked the core for components that needed to be transferred, such as dowel pins and brackets. Everything had been removed, so I loaded the core and headed back to the shop.
When I got back the core was unloaded and placed on the drain bench. I did not know what was wrong with this unit, as I had not taken the original call. However, when we drained it, yuck, did this fluid stink, and it was black – and look at the nice sparkles.
The next day we received a call from the shop that there was a problem. Like fingernails on a chalkboard, this made us 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 needed to know symptoms and codes that were present before they started working on the truck. I knew the old transmission was toast on the basis of the fluid color and condition. However, if there was still an issue, that told me the transmission was a victim and not the culprit.
We made arrangements 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 seriously, and they take top priority.
I grabbed the paperwork and scan tool and headed out to solve the mystery. The other shop did not have any information other than that the truck barely moved when they got it, so there was no history of codes. When I plugged in the scan tool 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 OK. 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 we went to the other end. I checked for proper voltage going to the PCM at pins 71 and 37. These were both OK. Next was a quick check of pin 87, which supplies power to the transmission; it was OK.
Now we had the answer – a bad wire from the PCM to the transmission. We called the shop to explain what we had found and get the OK 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 from the PCM to the transmission. Did we need to just run a new power wire or was there more? Guess what – no reading on multiple wires, so we had either a smashed or damaged harness. I couldn’t see a darned 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-sized area that was now one melted-together glob. A short time later, after splicing and repairing the wires with connectors, solder and heat-shrink tubing we had it all back together. Now to stuff the harness back in without the truck eating my hands.
I got back in the seat of the truck with the scan tool plugged in and, voila! No codes. I headed out on the road for a comprehensive road test. The transmission shifted great and had 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. We then called the shop to let them know the 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-looking and burnt, slips in the parking lot – yes, it will need the transmission replaced, 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” that what they are doing is telling us there is more than one problem and they need our help.
Carman Klaber joined Certified Transmission in 2003 as a technician and is now the diagnostician at the store in Olathe, Kan.