P04D0: Exhaust Gas Recirculation Temperature Sensor C Circuit Low
What to do
Ask for the wiring near the exhaust and EGR cooler to be inspected before the sensor is replaced. On this kind of sensor a short to earth reads exactly like an impossibly hot sensor, and a wire chafed against a hot pipe is the usual cause — much cheaper than a part.
Mention if the fault comes and goes with the weather. Appearing in the wet and clearing when dry points firmly at water in a connector.
Ask which part of the system this third sensor watches on your engine, since it varies and the answer decides where the garage looks.
The car will usually drive normally, but the emissions system will not be working as intended.
What this code means
The third EGR temperature sensor's signal is below the lowest voltage the circuit should produce.
A third EGR temperature sensor means a more complex recirculation system than most, and identifying what it watches is the first step. Two arrangements are common: an engine with both high-pressure and low-pressure EGR, where each path is monitored separately, or a V engine with a cooler per bank.
On these thermistor circuits, low voltage means the opposite of what it sounds like. Resistance falls as temperature rises, so a low signal corresponds to a very hot sensor — and a short to ground produces the same reading as an impossibly hot one. They are electrically identical.
So a circuit-low code on a temperature sensor almost always means a short, not heat. Check the wiring before believing the temperature.
Location makes shorts likely here. These sensors and their harnesses run close to the exhaust and the cooler, where insulation hardens and eventually fails against the metal it is resting on. A wire chafed against a hot pipe is the classic finding.
Water in the connector does the same thing and is why the fault often appears in wet weather and clears in dry.
Unplugging the sensor separates wiring from element in a minute: a circuit that stays low with the sensor disconnected is a harness fault.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Heat damage to wiring insulation · moderate
- Water ingress into connector · easy
- Corroded or loose connector · easy
Less common
- Faulty EGR temperature sensor · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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