P2478: Exhaust Gas Temperature Out of Range — Bank 1 Sensor 1
What to do
Alone, this is usually a drifting sensor caught by its own plausibility window. With fuelling or filter codes alongside, treat the temperature as possibly real — which changes it from a sensor errand into a promptly-investigated one.
What this code means
The first sensor's temperature is out of range — not the circuit family's electrical verdict, but the measured value itself outside what this position can physically read while the engine does what it is doing.
That distinction forks the diagnosis in a way worth stating once for the pair: either the measurement is wrong or the temperature is real. The measurement side is the P2080 drift story. The real side is the interesting one — sensor 1 sits closest to the engine, and a genuinely out-of-range reading there can be combustion running hot (timing, over-fuelling, a regeneration overshooting) arriving at the thermometer first. Companion codes decide: this code alone leans sensor; this code with fuelling or regeneration codes leans real, and the P2428 respect for genuinely hot exhausts applies.
Likely causes
Start here
- Sensor drifted out of calibration · moderate
- Faulty exhaust gas temperature sensor · moderate
Less common
- Leaking fuel injector · moderate
Symptoms
Components involved
Information, not instruction
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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
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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