GM/Detroit 6.5L ENGINE CONTROLS – DTC P0236 Turbocharger Boost System Performance

Circuit Description
The PCM operates a solenoid to control boost. This solenoid is normally open. By providing a ground path the PCM energizes the solenoid which then allows vacuum to pass to the wastegate valve. During normal operation, the PCM compares its wastegate duty cycle signal with the boost signal and makes corrections in the duty cycle accordingly.

Conditions for Running the DTC
• The PCM performs this DTC diagnostic continuously.
• The engine speed is more than 2400 RPM.
• The fuel rate is more than 20 mm.
• The engine speed is more than 1800 but less than 2400 RPM.
• The fuel rate is more than 20 mm.

Conditions for Setting the DTC
• The boost pressure is more than or less than 20 kPa from desired (internal to PCM).
• All diagnostic conditions met for 10 seconds.

Action Taken When the DTC Sets
• A poor performance condition will exist.
• The PCM will reduce maximum fuel.
• The PCM will disable TCC.

Conditions for Clearing the M IL/D TC
• The PCM will 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
A vacuum leak or a pinched vacuum line may cause a DTC P0236. Check all vacuum lines and components connected to the hoses for leaks or sharp bends. Check vacuum source. A possible EGR DTC will store if there is a problem with the vacuum source. Also check for proper vacuum line routing.

The turbocharger wastegate actuator uses a pulse width modulated vacuum solenoid that causes vacuum to fluctuate under normal conditions. A steady vacuum reading indicates a restricted or plugged solenoid vent filter or solenoid vent orfice.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
4. This will check the wastegate solenoid and filter. If the filter is plugged, the filter will not allow the solenoid to vent and this will cause an overboost condition.
5. This step checks the turbocharger wastegate actuator for vacuum leaks. The actuator must hold vacuum.
6. This step will check for vacuum leaks at the lines.
9. This step will check for a skewed boost pressure sensor.


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