DTC 31

DTC 31 Circuit Diagram:

DTC 31 Diagnostic Chart Turbo Wastegate Overboost:

CIRCUIT DESCRIPTION:

Exhaust pasing in the exhaust spins a turbine, which in turn spins an impeller which is in the intake air stream. This forces more into the engine, thereby increasing engine output.
The wastegate is normally closed, but opens to prevent an overboost condition. The wastegate opens when when pressure is applied to the controller (diaphragm). Pressure to the diaphragm is controlled by an ECM controlled duty solenoid. A boost increase will be detected by the MAP sensor and the ECM will "pulse" the solenoid. Under normal driving conditions, the solenoid is energized which closes off the pressurized air passage to the diaphragm. This allows full turbo boost. When the ECM detects excessive boost pressure, it cycles the solenoid on and off, allowing boost pressure to act on the diaphragm. The diaphragm moves the wastegate allowing exhaust gas to bypass the turbine, slowing the turbine. As boost pressure reduces, the ECM energizes the solenoid and boost pressure in the diaphragm bleeds off through the vent in the solenoid. If overboost cannot be reduced through the wastegate, the ECM will reduce fuel delivery to prevent engine damage.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. DTC 31 will set when manifold pressure exceeds 143 kPa of boost for 2 seconds and DTC 33 has not been previously set. DTC 31 will set, but the CHECK ENGINE light will only stay on during the over boost period and for 10 seconds afterward.

An over boost condition could be caused by:
^ WHT/PPL wire shorted to ground.
^ A sticking wastegate or actuator.
^ A control valve stuck in closed position.
^ A cut or pinched control hose.
^ A faulty ECM.
^ An extremely dirty air filter.

2. After the 103 Kpa is applied to the valve and then the pressure source is removed, the actuator should slowly move back and close the wastegate. If the pressure does not bleed off, the vent in the solenoid could be clogged.

3. With the key ON and the diagnostic terminal grounded, the solenoid should be energized. This closes off the manifold to the wastegate actuator.

4. Checks the electrical portion of the system. With the key ON and engine OFF, the solenoid should not be energized.