What does it mean?
Bi-fuel and dedicated gaseous fuel vehicles store compressed natural gas, liquefied petroleum gas or a similar alternative fuel in a pressure tank, and a pressure sensor on tank A reports the stored pressure. The module uses that value to work out how much fuel remains, to control the regulator and to decide when the engine may run on the gaseous fuel. This code is the electrical circuit fault: the module cannot obtain a valid signal because the reference, signal or ground path is open, shorted or otherwise unusable. Without a trustworthy pressure value the system normally blocks or ends operation on the alternative fuel and keeps the engine on petrol.
Symptoms
- Vehicle refusing to change over to the alternative fuel and running only on petrol
- Gas tank level showing empty or not displayed at all
- MIL (check engine lamp) on together with a gas system warning indicator
- Unexpected switch back to petrol while driving
- Refuelling of the gas tank not being recognised by the system
- Reduced range and higher running cost until the fault is repaired
Likely causes
- Open or shorted signal, reference or ground wire in the tank sensor harness
- Connector corrosion or water intrusion, common where the harness runs under the vehicle near the tank
- Sensor internally failed, or damaged by frost, impact or an overpressure event
- Harness chafed or crushed against tank straps, the underbody or a heat shield
- Poor ground connection at the gaseous fuel control module
- Sensor not correctly tightened into its port, or its seal damaged during service
- Rarely, a failed input inside the gaseous fuel control module
How to fix it
- Read the reported tank pressure with the key on and compare it with a mechanical gauge value where the system allows one
- Inspect the sensor connector under the vehicle for corrosion, water and backed out terminals
- Measure reference voltage and ground at the sensor connector with the key on
- Check continuity and insulation of the signal wire back to the control module while flexing the harness
- Repair chafed or crushed harness sections and reroute them away from straps and sharp edges
- Depressurise the system following the correct safety procedure before removing the sensor, then fit a new one if the wiring proves good
- Clear the code, refill or repressurise as required and confirm that changeover to the alternative fuel now works