P2A4C Alternative Fuel Temperature Sensor Range/Performance

Here the gas temperature reading is electrically valid but implausible. A typical check compares it with other temperatures after a long cold soak, when gas, intake air and coolant should agree within a few degrees; another looks for the cooling that expansion in the regulator causes under heavy gas flow. A sensor that sticks at one value or lags far behind fails such tests. CARB requires rationality checks of this kind for inputs that affect fuel metering. Because the mass of gas injected depends on its density, a temperature that is wrong but in range quietly shifts the mixture, which the fuel trim then has to absorb. No manufacturer publishes P2A4C or its limits; Roush's propane equivalent is P0181. A sensor with a poor thermal contact can also cause it.

Likely causes

Symptoms

• Check engine light after a drive cycle
• Fuel trim off while running on gas
• Often no noticeable driving issue

Repair estimate

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

Parts involved

Related codes

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