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.

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

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

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

Use the Manual With the Right Hardware

When to See a Mechanic