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.

Posted by PerDiezel Solutions on January 18, 2026

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.

Cummins ISB CM850 (2003-06) Fault Code: 2556 PID: SID 70 SPN: 729 FMI: 4 Intake Air Heater #1 Circuit – Voltage Below Normal or Shorted to Low Source. Low voltage detected at the intake air heater signal circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2555 PID: SID 70 SPN: 729 FMI: 3 Intake Air Heater #1 Circuit – Voltage Above Normal or Shorted to High Source. High voltage detected at the intake air heater signal circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2554 PID: 95 SPN: 1209 FMI: 2 Exhaust pressure sensor circuit – data erratic, intermittent, or incorrect. An error in the exhaust pressure sensor signal was detected by the ECM.

Cummins ISB CM850 (2003-06) Fault Code: 2448 PID: SPN: 111 FMI: 17 Coolant Level – Data Valid But Below Normal Operational Range – Least Severe Level. Low engine coolant level detected.

Cummins ISB CM850 (2003-06) Fault Code: 2388 PID: SID 269 SPN: 2795 FMI: 13 Variable Geometry Turbocharger actuator position failed automatic calibration procedure – out of calibration.

Cummins ISB CM850 (2003-06) Fault Code: 2387 PID: SID 146 SPN: 2975 FMI: 7 Turbocharger actuator motor – the mechanical system is not responding properly or is out of adjustment. Turbocharger actuator is not responding or is slow to respond.

WARNING!