Powertrain, generic (extended)

P2A4B Alternative Fuel Temperature Sensor Circuit

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

Gaseous fuel changes density with temperature, so gas systems measure it to meter the right mass; Ford's 2003 bi-fuel CNG trucks, for example, use a thermistor at the rail for that density calculation and only switch to gas once both temperature and pressure allow it. The title of P2A4B names no location, which sets it apart from the tank temperature codes (P01AA ff.), the rail temperature codes (P01B4 ff.) and the vaporizer outlet sensors (P2A50 ff.). It is the general circuit fault of this gas temperature input, without a low or high verdict. No manufacturer documents P2A4B; Roush's propane systems report their fuel temperature under P0181–P0183 instead. Inspect plug, wiring and sensor resistance, since an NTC sensor can be checked against temperature with an ohmmeter.

Likely causes

Plug or wiring of the gas temperature sensor faulty

Temperature sensor element defective

Input stage or data link of the gas module disturbed

Symptoms

Check engine light
Bi-fuel vehicle stays on petrol or switches back
Rougher running on gas

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€80–450

Time0.5–2 h

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

Parts involved

alt fuel temperature sensorwiring harnessafcm

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