Recently installed a used 3.8 engine and AX4S transmission. Worked fine for about 3 weeks then intermittently the trans. won't shift and the "o/d off" light flashes. First start-up in the morning tends to work fine, but at first stop, problem starts. Has P0720 DTC. Understand that this is speed sensor circuit. Would like to know where are the most common vulnerable points for this code. Oddly, transmission worked fine all day yesterday. (July 30)
The flashing OD light indicates a diagnostic present, getting it scanned will let you know which code. Check fluid level and condition, may give you an indication.
Most likely, the computer saw something happen in the transmission that was enough to trigger the OD light to flash. Most likely, a code was set in memory. To retrieve the code most parts stores will allow you to pull codes for free with a code reader.
OK Bert, should I be looking at replacing the speed sensor or looking for a faulty circuit?
Sorry Bert, thank you. I was a little hasty and did not look at the code explanation.
Before spending the money on the sensor, try cleaning the connector. The car has a little age on it, corrosion happens. I've had to clean several connectors on our 04 Pontiac. Spray some electronics cleaner on the male and female pins, then apply some dielectric grease.
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