Standard Emissions

CODE 51 EXHAUST GAS RECIRCULATION CIRCUIT

DTC 51 EGR Checkout:

EGR Control Circuit:

CIRCUIT DESCRIPTION
The Exhaust Gas Recirculation Solenoid Vacuum (EGR SV) valve is controlled by the Engine Control Module (ECM). System voltage is applied to the EGR SV valve from the Fuel Injection (FI) relay. When the driver in the ECM closes, the EGR SV valve solenoid is activated.

Diagnostic Trouble Code (DTC) 51 will set if the following conditions are met:
^ System is operating in closed loop operation.
^ Manifold Absolute Pressure (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 EGR SV valve could cause a Diagnostic Trouble Code (DTC) 51.

DIAGNOSTIC AIDS
A poor or loose connection at the ECM could cause an intermittent failure. This could cause a DTC to be set falsely.

Closely check all vacuum hoses to the throttle body fuel injection (TBI) 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 SV valve. 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.

For EGR system mechanical diagnosis, refer to Emission Control Systems / Exhaust Gas Recirculation / Testing and Inspection.