DTC 31

Code 31 Chart:

Code 31 Wiring Diagram:

CIRCUIT DESCRIPTION:

On turbocharged engines, the exhaust gases pass from the exhaust manifold through the turbocharger, turning the turbine blades. The compressor side of the turbocharger also turns, pulling air through the air filter and pushing the air into the intake manifold, pressurizing the intake manifold. The wastegate is normally closed, but opens to allow exhaust gas to bypass the turbine to prevent an "overboost" condition. The wastegate will open when pressure is applied to the actuator. Pressure to the actuator is controlled by a wastegate control valve solenoid pulsed "ON" and "OFF" by the ECM. Under normal driving conditions the wastegate control solenoid is energized all the time which closes "OFF" the manifold pressure to the wastegate actuator. This allows for a rapid increase in boost pressure. A boost increase will be detected by the MAP sensor, and the ECM will pulse the wastegate control valve. Manifold pressure will the be allowed to pass to the wastegate actuator, and the actuator will open the wastegate. This will prevent an overboost condition on heavy acceleration. As boost pressure decreases, the ECM closes the control valve and the wastegate pressure bleeds "OFF" through the vent in the control valve. If an overboost does exist as indicated by the MAP sensor, the ECM will reduce fuel delivery to prevent damage to the engine.


NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.


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

1. A code 31 will set when the manifold pressure exceeds 143 kPa (20 psi) of boost for 2 seconds, and a code 33 has not previously been set. Code 31 will set, but the "SERVICE ENGINE SOON" light will stay "ON" only while the overboost exists. The light will stay "ON" for 10 seconds after the condition exists and then go "OUT". With ignition shut "OFF", the control valve solenoid is open.

An overboost condition could be caused by:

^ CKT 435 shorted to ground.
^ A sticking wastegate actuator or wastegate.
^ A control valve stuck in the closed position.
^ A cut or pinched hose.
^ A faulty ECM.
^ An extremely dirty air filter.

2. After the 103 kPa (15 psi) is applied to the valve and the pressure source is removed, the actuator should slowly move back allowing the wastegate to close. If the pressure does not bleed off, the vent in the control valve solenoid could be plugged.

3. With ignition "ON" and the diagnostic terminal grounded, the control valve solenoid should be energized. This closes "OFF" the manifold to the wastegate actuator.

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