P2A5D: Alternative Fuel Vaporizer C Outlet Temperature Sensor Circuit High
What to do
The car will usually stay on petrol, or take much longer than usual to switch to gas. Nothing is dangerous and the car drives normally. Before suspecting the gas system, mention whether the heater takes a long time to get warm — a thermostat stuck open delays changeover and is a common, cheap cause.
What this code means
The circuit for the outlet temperature sensor on gaseous fuel vaporizer C is faulty.
The vaporizer is the part of a gas system with no petrol equivalent at all, and understanding it explains most of how a bi-fuel car behaves.
LPG leaves the tank as a liquid and has to reach the injectors as a gas. The vaporizer — installers usually call it the reducer — drops the pressure and lets the liquid boil off. And boiling absorbs heat: the same physics that makes a gas cylinder frost over when you draw from it hard. Left alone, a vaporizer would freeze itself solid within a minute and stop working.
So it is plumbed into the engine's coolant circuit. Engine heat replaces the heat that vaporisation removes. That single fact explains the whole starting sequence — the car runs on petrol until the coolant is warm, because until then the vaporizer cannot produce gas, and it is why a bi-fuel conversion always has hoses running to what looks like a small radiator on the bulkhead.
This sensor measures the temperature of the gas leaving it, and it is doing two jobs. It is the changeover permission — too cold and the system stays on petrol. And it is the fuel-density input, because the mass of gas in a given volume depends on temperature, so the injector timing depends on this reading.
Which is why the failure most often shows up as a car that will not change over, and why the diagnosis so often ends in the cooling system rather than the gas system. A thermostat stuck open delays every changeover on every journey while producing no other complaint anyone connects to it.
A second and third vaporizer means a system large enough to need them — a commercial conversion, a large engine, or one tank feeding through more than one reducer. Losing one is a partial failure, so the car still changes over and simply cannot deliver full power on gas, which reads as a vague loss of performance rather than as a fault.
At or above the upper limit, usually an open circuit.
Likely causes
Start here
- Faulty alternative fuel vaporizer · specialist
- Corroded or loose connector · specialist
- Open circuit in sensor wiring · specialist
Less common
- Thermostat stuck open · moderate
- Damaged wiring harness · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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