P2478 code meaning
Exhaust Gas Temperature Out of Range (Bank 1 Sensor 1)
Powertrain system Generic code P24xx codes Check engine light
What P2478 means
Unlike the circuit codes, P2478 judges the temperature itself at the first exhaust probe of bank 1, usually ahead of the oxidation catalyst. Ford's 2015 diesel summary for the 6.7L and 3.2L engines groups it with the EGT circuit check: the test is high-side only and trips at roughly 1150 °C, because the PTC probe curve leaves no separate low threshold. Volkswagen's 2014 Golf data for the 2.0L TDI CJAA sets it when the gap between target and measured temperature exceeds 40 K, and bulletin 01 12 28 updated the 2012 Passat TDI (CKRA) software because the check was too sensitive. Overheating from overfuelling or a failing turbo is the real-world trigger, so the cause deserves attention before the probe.
P2478 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2478
- MIL on
- Power reduced to protect the exhaust parts
- Smoke or a hot smell from the exhaust in real overheating
Common causes of P2478
- Most likelyReal overheating from excess fuel or a leaking injector
- PossibleOverly sensitive diagnosis needing a software update (VW Passat 2012)
- PossibleProbe reading too high due to ageing
- Less likelyLack of air from a boost leak or turbocharger fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Egt sensor b1s1
What each part of P2478 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 78 | The exact fault in that area. |
What to do next
- Note P2478 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2478
What does P2478 mean?
P2478 means "Exhaust Gas Temperature Out of Range (Bank 1 Sensor 1)". Unlike the circuit codes, P2478 judges the temperature itself at the first exhaust probe of bank 1, usually ahead of the oxidation catalyst. It is a generic code, so it means the same on every make.
Is it safe to drive with P2478?
Drive gently and only to a workshop. With P2478 the car can go into limp mode (reduced power) to protect itself.
Will P2478 fail an emissions test?
Yes, it can. P2478 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2478 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P2478 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.