P01B5: Alternative Fuel Rail Temperature Sensor Performance

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. P01B5 is the plausibility fault: the reading is valid but does not fit the expected gas temperature.

High severity. Can I keep driving?If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.

Symptoms

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

Most likely causes

Sensor drifting or stuck
Regulator coolant heating faulty (gas genuinely too cold)
Contact resistance in the connector

What to check, in order

Start with the simplest. You can tick off each step.

If you smell gas, shut off the supply, ventilate and do not start the engine
Compare the reading with other engine data while varying the engine speed.
Read the codes with a compatible scanner
Check the connectors and wiring of the component indicated
Leave any work on the gas circuit to an authorized shop

Good to know

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P01B5 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
1: Air and fuel
B5: Specific fault in that system

Frequently asked questions

Can I keep driving with code P01B5?

If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.

What causes code P01B5?

The most common causes are: sensor drifting or stuck; regulator coolant heating faulty (gas genuinely too cold); contact resistance in the connector.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.