P01B8Alternative Fuel Rail Temperature Sensor Circuit Intermittent/Erratic
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Check engine light on
- Gas operation blocked or switch to petrol
- Mixture errors or stumbling in gas mode
- Likely causes
- LikelyLoose contact or corrosion at the connector
- PossibleHarness chafed along the gas line or underbody
- PossibleSensor unstable internally
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.