Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
- 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.
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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.
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