GM/Detroit 6.5L ENGINE CONTROLS – DTC P1656 Wastegate Solenoid Control Circuit

Circuit Description
The turbocharger wastegate is a vacuum actuated valve used to control the exhaust gas heat sent to the turbo. The wastegate pulse width modulated solenoid meters the vacuum level at the wastegate valve actuator as commanded by the PCM. When the PCM is commanding the wastegate solenoid ON, the voltage potential of the circuit will be low (near 0 volts). When the PCM is commanding the wastegate solenoid OFF, the voltage potential of the circuit will be high (near battery voltage). The primary function of the PCM in this circuit is to supply the ground for the wastegate solenoid.

Conditions for Running the DTC
The ignition switch in the ON position.

Conditions for Setting the DTC
• The voltage on the wastegate solenoid control circuit is high (near battery voltage) when the EGR vent is requested ON.
or
• The voltage on the wastegate solenoid control circuit is low (near 0 volts) when the EGR vent is requested OFF.

Action Taken When the DTC Sets
• The PCM il l uminates the malfunction indicator lamp (MIL) on the second consecutive drive
trip the diagnostic runs and fails.
• The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC
• The PCM wil l turn the MIL off after three consecutive trips without a fault condition.
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The use of a scan tool.

Diagnostic Aids
This diagnostic will set when the control circuit does not follow the PCM command (when the solenoid is requested ON vol tage will drop, when the solenoid is OFF ignition voltage will be present). The scan tool has a 5 second ON time abort. The wastegate solenoid can be commanded ON for as many times as needed, in 5 second intervals. It’s possible DTC P0236 may set along with DTC P1656. This diagnostic can be checked during key up. The engine will not respond to scan tool commands at idl e (engine unable to achieve boost pressures greater than BARO at idle) or at any engine speed greater than idle (PCM control aborts to prevent engine damage).

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. Checks that both the ON and OFF states are commanded. Repeat the commands as many times as necessary.
3. This check can detect a partially shorted coil which would cause excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm, the coil may open (amps drop to zero), or short (amp draw greater than 0.75A).
14. If no trouble is found in the control circuit or the connection at the PCM, the PCM may be malfunctioning. However, this is an extremely unlikely failure.

 

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