P04D1: Exhaust Gas Recirculation Temperature Sensor C Circuit High
What to do
Ask for the connector to be checked first — including simply that it is plugged in. On this kind of sensor a broken connection produces exactly this reading, and a sensor left disconnected after EGR cleaning or cooler work is a common and free-to-fix cause.
Mention any recent work on the EGR system, cooler or exhaust.
Ask whether other sensors are also reading oddly. If several are, the fault is usually a shared earth or power supply rather than several failed sensors — which is a much smaller repair.
The car will usually drive normally, but it is worth fixing before an MOT since the emissions checks will not complete.
What this code means
The third EGR temperature sensor's signal is above the highest voltage the circuit should produce.
This is the mirror of its low-side sibling, and on a thermistor the interpretation inverts too. High voltage corresponds to high resistance, which means a very cold sensor — and an open circuit produces the highest reading of all. A broken wire and a sensor at −40°C look identical to the module.
So this is an open-circuit code until proven otherwise.
The practical order of investigation:
- Is it plugged in? A sensor left disconnected after EGR or cooler work produces this exactly, and on a recently serviced vehicle it costs nothing to check.
- Is the connector sound? These live in heat and soot; terminals corrode and lose grip.
- Is the harness intact? Insulation hardened by exhaust heat cracks, and the conductor inside eventually breaks.
- Is the sensor's earth good? A lost earth floats the signal high, and the earth is easy to overlook.
Only after all four does the sensor itself become the answer — real, but the cheapest possibilities come first and they are genuinely more likely.
Where several EGR sensors read implausibly at once, look at the shared reference or earth rather than at the sensors. That pattern recurs across this corpus and it is the single most expensive thing to misread.
Likely causes
Start here
- Open circuit in sensor wiring · moderate
- Corroded or loose connector · easy
- Sensor left disconnected after previous work · easy
- Heat damage to wiring insulation · moderate
Less common
- Open sensor ground circuit · 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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- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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