Open or damaged signal wire between the EGR temperature sensor and the engine computer; Corroded, loose, or disconnected electrical connector at the sensor; Failed EGR temperature sensor (open thermistor element); Short to voltage on the signal circuit, often from chafed wiring near hot exhaust components; Faulty engine computer (rare, but possible if internal pull-up resistor fails); Excessive carbon buildup on the sensor tip causing an open circuit

DTC codes / P04xx · Auxiliary emission controls / P040D

P040DEGR Temperature Sensor A Circuit High

Q: What does code P040D mean?

EGR Temperature Sensor A Circuit High. P040D means the engine computer has detected an abnormally high voltage on the signal circuit of the exhaust gas recirculation (EGR) temperature sensor, which is typically a thermistor that changes resistance with temperature. The high voltage tells the computer that the sensor circuit is open, shorted to voltage, or that the sensor is reporting an unrealistically cold temperature.

P040D means the engine computer has detected an abnormally high voltage on the signal circuit of the exhaust gas recirculation (EGR) temperature sensor, which is typically a thermistor that changes resistance with temperature. The high voltage tells the computer that the sensor circuit is open, shorted to voltage, or that the sensor is reporting an unrealistically cold temperature.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Rough idle or stumbling when the EGR valve opens
Poor fuel economy or increased emissions
Hesitation or surging during light acceleration
In rare cases, a no-start condition if the EGR system is commanded fully open

Common causes, most likely first

Open or damaged signal wire between the EGR temperature sensor and the engine computer
Corroded, loose, or disconnected electrical connector at the sensor
Failed EGR temperature sensor (open thermistor element)
Short to voltage on the signal circuit, often from chafed wiring near hot exhaust components
Faulty engine computer (rare, but possible if internal pull-up resistor fails)
Excessive carbon buildup on the sensor tip causing an open circuit

How to diagnose and fix it

Connect a scan tool and record the EGR temperature sensor voltage and freeze-frame data to confirm the high-voltage condition
Visually inspect the sensor, connector, and wiring for damage, corrosion, or loose pins, and repair as needed
Measure resistance across the sensor terminals and compare to the manufacturer's temperature-resistance chart to verify sensor integrity
Back-probe the signal circuit at the sensor and at the computer to check for an open or short to voltage with the key on
If wiring and sensor test good, substitute a known-good sensor or simulate the signal with a resistor box to see if the code clears
Clear the code and perform a road test with the EGR system commanded on to confirm the repair
If the code returns and all circuits test normal, follow the manufacturer's diagnostic flow for computer internal fault verification

What the high-voltage reading really means

A high voltage on a thermistor circuit almost always indicates an open circuit, not a sensor that is reading too hot, so chasing overheating symptoms leads nowhere.
Carbon buildup on the sensor tip can insulate it and create an open circuit that only appears when the EGR valve is closed and the sensor cools.
Wiring chafing near the exhaust manifold or turbocharger is a common hidden cause that a simple sensor replacement will not fix.
Some vehicles use the EGR temperature sensor to infer EGR flow, so a P040D can be accompanied by EGR flow codes even when the valve itself is fine.
A faulty engine computer is the last suspect, but a shorted internal pull-up resistor can mimic a sensor circuit fault and is often overlooked.

Can I keep driving with P040D?

You can usually continue driving with P040D because the engine computer will default to a safe EGR strategy, but avoid heavy acceleration or towing until the fault is repaired to prevent potential engine knock or increased emissions.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.