Ford Explorer Problems

1999 FORD EXPLORER 4x4 5.0l come into the shop for a no shift and no power problem.

The customer comes in saying that he needs the transmission rebuilt because some other shop already diagnosed the problem and found it to be a transmission problem. Since we specialize in transmissions he just wanted us to rebuild it. And so we did. Even though he had codes set on the computer for transmission and engine issues he still wanted us to just rebuild the transmission.

TRANSMISSION PROBLEMS?

So a rebuilt transmission was put in the car and guess what …yup you guessed it… the car still had exactly the same problem. No shift, no power, and the same codes came back as soon as we started the car. The codes were:

· P0135 – oxygen sensor heater fault bank1 sensor1

· P0155 – 02s heater fault b2 s1

· P0232 – fuel pump secondary circuit high

· P0230 – fuel pump primary circuit malfunction

· P0743 – tcc system electric

· P0750 – shift solenoid A malfunction

· P1747 – pressure control solenoid A

Originally we should have diagnosed the issue but the customer refused the diagnosis, so after having pulled and reinstalled a transmission, finding the same problem, we had to do the diagnostics properly in order to find the real problem. For that we needed to charge him.

When doing a diagnostic the first thing that I always do is a visual check. Just look for obvious stuff like a broken wire or a blown fuse, stuff like that. I noticed that someone was trying to fix the main wiring harness (very bad job by the way) and to make sure that they did it correctly I had to open it apart and check that the wire colors matched. They all seemed to be ok. Then it was time to pull some diagrams and after looking for a couple of minutes I noticed that all the codes listed above share one thing in common; fuse #13 in the power distribution box under the hood. It is a 15a mini fuse, which seemed to be ok.

After a closer look I found out that they crossed two wires. Even though they are the same color and size they are used to control different components in the car. Both light blue/orange wires at the main harness where crossed.

One of the wires is the power feed to the transmission solenoid, oxygen sensor and EGR solenoid. The other one is used by the PCM (powertrain control module) to control the fuel pump relay.

Here is what happened; the PCM was cutting fuel from the injectors because it couldn’t control the epc (pressure regulating solenoid) and because it couldn’t control the EPC to the transmission his reaction is to shut the injector pulse so the engine doesn’t have enough power to ruin the transmission.

So after I replaced the main harness with a new one (the old one was in very rough shape) the car was like new.

Click thumbnail to view full-size
main wiring harness
main wiring harness
main wiring harness

Comments 1 comment

Kevin 6 years ago

I found this article really useful, THANKS!!

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