Code 51, EGR Circuit (CALIF. Only): Notes

Exhaust Gas Recirculation (EGR) temperature sensor is mounted on top of EGR valve. EGR temperature sensor is a variable resistor that changes along with temperature of exhaust gases. ECM applies 5 volts to EGR temperature sensor and reads voltage across sensor. As exhaust gas temperature increases, sensor resistance decreases providing ECM with a low voltage input. When exhaust gas temperature decreases, sensor resistance increases providing ECM with a high voltage input. ECM calculates exhaust gas temperature by voltage inputs received.

Code 51 will set when one of the 2 following conditions are met:

• EGR temperature sensor is shorted with engine coolant temperature less than 104°F (40°C) and exhaust gas temperature is greater than 428°F (220°C) for at least 3 seconds.
• EGR temperature sensor is open with engine coolant temperature greater than 158°F (70°C) and intake air temperature is greater than 122°F (50°C) for at least 80 seconds.
  NOTE: Test numbers refer to test numbers on diagnostic chart.

1. Checks for proper EGR valve operation.
2. Checks for 5-volt reference to EGR temperature sensor.
3. Checks for short to voltage in Red/Green wire.
4. Checks for open Gray/Yellow wire, a faulty ECM or EGR temperature sensor.