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I have an early 99 F350, 7.3. The overdrive flashes, sometimes stops flashing while driving, sometimes not. Always stops flashing after shutting off and restarting. I checked the codes and have P0720. Need help troubleshooting the problem. Mark.... please help! Attached screenshots of DTC readout.
There is an electrical issue with the Output Speed Sensor, located on the back end of the transmission. Usually, the problem is in the wiring between this sensor and the PCM, but it is also possible that the sensor itself has failed.
The two wires from the PCM to the sensor need to be checked from one end to the other for continuity, short to ground, and short to power. If the wiring checks out, the sensor is the problem. I'm betting on the wiring having an issue, not the sensor.
There is an electrical issue with the Output Speed Sensor, located on the back end of the transmission. Usually, the problem is in the wiring between this sensor and the PCM, but it is also possible that the sensor itself has failed.
The two wires from the PCM to the sensor need to be checked from one end to the other for continuity, short to ground, and short to power. If the wiring checks out, the sensor is the problem. I'm betting on the wiring having an issue, not the sensor.
You wouldn't happen to know which wires they are on the PCM end? Or know where I can get a diagram to figure out which wires are which at the PCM? Thanks Mark...
Archie.....
Ok, thanks. One more question, checking for short to power.... where's power? And when checking for shorts do the connectors have to be disconnected at both the sensor and PCM? Sorry, that was 2 more questions lol
I found a whole bunch of potential causes/repairs for this code, as I reported when I "bumped" the thread.
Please read the disclaimer on the "bump" carefully, I reported everything I found without making judgements, but I did indicate which repairs reduced or eliminated the frequency the code was sent.
Mark is correct that the problem is usually dirty or corroded contacts in the connectors, assuming there are no other electrical issues in your truck, Mine were dirty, but I had bad ignition coils (V10) and a loose battery connection too...
The code has not returned since September when I went through the connectors.
Ok, so I ohmed out the wires looking for opens and shorts like Mark said. That all seemed to be good. So then I put the ohmmeter across the pins on the sensor and it read open. Replaced the the sensor and it hasn't set any codes since!. Thanks guys. Thanks Mark!
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