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2003 Subaru Legacy sedan L no speedo 2.5 A/T, AWD
by moparjohn on Aug 21 2017, 4:09 PMshowed up with code P0502, TCM calculates road speed from front axle sensor, 16 pulse per revolution, this signal is good and within spec.the TCM then converts this signal to a 4 pulse per revolution and sends it out to dash cluster and the PCM, this signal appears to be weak as there is no speedo movement and PCM PID list shows 0 MPH. I have checked the wiring between these units and it is good. Tried a used TCM no luck. Output from TCM is nice square waveform but only .25 volt, dont know if this is correct or not...
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1. Clear the codes and see which ones reset. If just P0502 sets, check vehicle speed sensor 2 for signal.2. If P0866 and P1698 set check for voltage on pins D19 Pink wire at the ECM, this should be between 1-4 V normally. This voltage is modified by the TCM, if the voltage is high check for a short to power. If no short to power is noted, likely the TCM is not communicating. Pin C15 Yellow wire at the ECM should have about 8 V, this is a voltage that is supplied by the TCM. If no voltage is noted, check for voltage right at the TCM on pin A2 without sport shift, B10 with sport shift. If no voltage is noted here, the TCM may have failed.
3. Check TCM powers and grounds. Powers are B6 Yellow/Red (without sport shift), B12 White/Black (with sport shift), A23 and A24 Green/Red wires. Grounds are B9 and B19 Brown/White wires (without sport shift) or A21 and C19 Brown/White wires (with sport shift).