I have a 2007 Ford Expedition, and recently I noticed that the transmission was behaving oddly. I don't do much towing, and I have serviced the vehicle more frequently than the manufacturer's recommendations, so I didn't expect any transmission trouble. I checked the transmission fluid. It was clean and pink with no visible signs of wear, and it was at the proper level. I checked my logbook, and there were 15,000 miles on the fluid. The transmission kept behaving badly. The main issue is that the car was not selecting the proper gear when stopping and restarting. This happened repeatedly for a few weeks. Then it failed to start when the transmission was hot.
That pointed to electronics in my mind. After it cooled off for a few hours, the vehicle would start again. On this model, the transmission controller is inside the transmission above the valve body, which was not a normal user-serviceable location. I took it to a transmission shop, and the mechanic could see the problem. He also downloaded a fault code. He informed me that the dealer is the only place to get the transmission control module reprogrammed, so his recommendation was a trip to the dealer.
Troubleshooting at the dealer revealed that the problem was not the transmission controller. Instead, it was the wire bundle that feeds transmission information to the engine controller. This bundle is routed directly above the passenger side catalytic converter on its way to the ECU. There is one plastic clip that prevents the wire bundle from contacting the catalytic converter.
It was that $0.50 clip that had failed and allowed the wire bundle to contact the catalytic converter. Needless to say, I was impressed that the wire bundle wasn't a pile of slag on the garage floor. After $600 at the local dealer, the vehicle was operating smoothly. I did take the extra step to verify that the wire bundle could not contact any hot portion of the exhaust.
While under the vehicle, I noticed that there is a wide spot available where the wire bundle could have been routed, and it would have created a four-inch gap between the bundle and the exhaust system. I also noticed that the new bundle had three more attachment clips, which tells me that it is a known issue -- just not communicated.
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