Cummins ISB CM850 (2003-06) Fault Code: 2557 PID: SID 57 SPN: 697 FMI: 3 Auxiliary PWM Driver #1 – Voltage Above Normal or Shorted to High Source. High signal voltage detected at the analog torque circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2557 PID: SID 57 SPN: 697 FMI: 3 Auxiliary PWM Driver #1 – Voltage Above Normal or Shorted to High Source. High signal voltage detected at the analog torque circuit.

The default setting for Transmission PWM output Type in INSITE? electronic service tool is 805. The PWM output only has meaning with non-electronic Allison Transmission? AT545. Older software and ECMs had no diagnostics on this output and having the default set at 860 was of no consequence. Newer software and ECMs do have a diagnostic if this output is selected but no hardware is connected. FC 2557 will be logged. Setting Transmission PWM Output Type in INSITE? electronic service tool to NONE may clear the fault code.

Possible causes:

1)A faulty transmission shift modulator
2)An open circuit in the output device driver return line
3)A short pin to pin in the output device driver line.

Possible repairs:

1)Replace the transmission shift modulator.
2)If the RETURN is wired to the ECM, repair or replace the OEM harness.
3)Replace the ECM.