P01B8 Alternative Fuel Rail Temperature Sensor Circuit Intermittent/Erratic

These codes only apply to vehicles with a gaseous alternative fuel – compressed natural gas (CNG) or LPG – as bi-fuel models alongside petrol or as dedicated gas engines; on bi-fuel vehicles a fault usually blocks gas operation and the vehicle runs on petrol. The gas rail temperature sensor, often combined with the rail pressure sensor, measures the gas temperature at the injectors: gas cools strongly when it expands in the regulator, and the injected mass depends on density, i.e. on rail pressure and temperature, so the module corrects injection time with it. A Ford patent describes plausibility checks against engine bay temperature at idle and an expected cold rail at full load with a full tank. Roush propane systems report rail temperature faults as P0181–P0183; no manufacturer document using exactly this code was found. P01B8 covers brief dropouts or jumps in the signal, typically a loose contact or heat-damaged wiring near the engine.

Likely causes

Symptoms

• Check engine light on
• Gas operation blocked or switch to petrol
• Mixture errors or stumbling in gas mode

Repair estimate

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

Parts involved

Related codes

References: law.cornell.edu, patents.google.com, static.nhtsa.gov, static.nhtsa.gov.