Powertrain Controls - ECM/PCM

DTC 51:

EGR Control Circuit:

CIRCUIT DESCRIPTION:
The EGR Vacuum Switching Valve (VSV) solenoid is controlled by the ECM. Battery voltage is applied to the VSV solenoid from the FI relay. When the driver in the ECM closes, the EGR vacuum switching valve solenoid is activated. DTC 51 will set if the following conditions are met:

^ System is operating in closed loop operation.
^ MAP is less than a calibrated value.

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

1. This will check the circuit for a short to ground.

2. Checks for voltage from FI relay.

3. Checks the circuit for short to ground or a faulty ECM.

4. Checks the circuit for an open GRN wire.

5. A high resistance in the solenoid coil could cause a DTC 51.

DIAGNOSTIC AIDS:
A poor or loose connection at the ECM could cause an intermittent failure. This could cause a code to be set falsely. Closely check all vacuum hoses to the throttle body and the EGR valve. Also check the MAP sensor vacuum hose for leaks or restrictions. In closed loop operation with EGR enabled, the ECM will periodically turn "OFF" the EGR VSV. If the corresponding manifold pressure change is less than a calibrated value, the ECM determines that a fault exists in the EGR system and sets a DTC 51.