Powertrain, generic (extended)

P2478 Exhaust Gas Temperature Out of Range (Bank 1 Sensor 1)

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

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.

Likely causes

Real overheating from excess fuel or a leaking injector

Overly sensitive diagnosis needing a software update (VW Passat 2012)

Probe reading too high due to ageing

Lack of air from a boost leak or turbocharger fault

Symptoms

MIL on
Power reduced to protect the exhaust parts
Smoke or a hot smell from the exhaust in real overheating

Repair estimate

DifficultyHardWorkshop job

Parts and labour€50–1,200

Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

egt sensor b1s1

References: fordservicecontent.com, static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.