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Auxiliary PWM Driver #1 – Voltage Above Normal or Shorted to High Source
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Overview
| CODE | REASON | EFFECT |
| Fault Code: 2557 PID: S057 SPN: 697 FMI: 3 LAMP: Amber SRT: |
Auxiliary PWM Driver #1 – Voltage Above Normal or Shorted to High Source. High signal voltage detected at the analog torque circuit. |
Can not control transmission. |
 Auxiliary PWM Driver #1 Circuit
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Circuit Description
The transmission shift modulator uses this signal from the ECM to determine when to shift the transmission. The return circuit is dependent on OEM wiring. It may be wired back to the ECM on some vehicles or wired to chassis or block ground on others. Consult the OEM wiring diagram for return circuit details.
Component Location
Refer to the OEM diagram for the location of the transmission shift modulator.
Shop Talk
The default setting for Transmission PWM output Type in INSITE™ electronic service tool is 80/65. 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 86/50 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.
This fault can be caused by the following:
- A faulty transmission shift modulator
- An open circuit in the output device driver return line
- A short pin to pin in the output device driver line.
Refer to Troubleshooting Fault Code t05-2557
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