1997 Ford F150 4x4 4.6L Engine Replacement: P0743 and P0708 Trouble Codes, Speedometer Failure, Overdrive Flashing, and Second Gear Shift Issue
After replacing the engine in my 1997 Ford F150 4x4 with a 4.6L V8, I'm now experiencing several transmission-related issues: the speedometer is not functioning, the overdrive light is flashing intermittently, and the truck will not shift out of second gear. The vehicle displays diagnostic trouble codes P0743 and P0708. These symptoms suggest a potential electrical or sensor issue within the transmission system, possibly related to communication between the engine and transmission control modules.
After installing a new engine, it's important to inspect the electrical harness connecting the transmission. Pay close attention to where the harness passes through the engine-transmission mating surface and near exhaust pipes—this area is prone to interference or damage. Also ensure that the Vehicle Speed Sensor (VSS) is properly connected and functioning, as its failure can trigger both P0743 and P0708 codes and cause speedometer malfunction and shifting problems.