Cause
Faulty alternative fuel vaporizer
The vaporizer — installers usually call it the reducer — that turns liquid LPG into gas has failed, scaled up internally, or lost its heating.
It is the part of a gas system with no petrol equivalent, and understanding it explains most of how a bi-fuel car behaves. LPG leaves the tank as a liquid and must reach the injectors as a gas. Boiling it off absorbs heat — the same physics that frosts a gas cylinder when you draw from it hard — so left alone a vaporizer would freeze itself solid within a minute.
That is why it is plumbed into the engine coolant circuit, and why a bi-fuel car always starts on petrol: until the coolant is warm there is no gas to burn. It also means a vaporizer fault and a cooling-system fault are hard to tell apart from the symptoms. A thermostat stuck open delays changeover on every journey while producing no other complaint anyone connects to it — worth eliminating before the vaporizer is condemned.
Its own failures are two. It scales up internally over years, transferring heat less well, which stretches changeover time so gradually that nobody can date it. Or its diaphragm perishes, which is the one that matters: a failed diaphragm can pass gas into the coolant circuit, so a converted car whose cooling system mysteriously pressurises is worth taking seriously.
These are usually aftermarket installations, so the work belongs with a gas installer rather than a general workshop.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (18)
Codes where this is a likely explanation first, rather than merely a possible one.
- P2A50 Alternative Fuel Vaporizer A Outlet Temperature Sensor Circuit Likely for this code High
- P2A51 Alternative Fuel Vaporizer A Outlet Temperature Sensor Range/Performance Likely for this code High
- P2A52 Alternative Fuel Vaporizer A Outlet Temperature Sensor Circuit Low Likely for this code High
- P2A53 Alternative Fuel Vaporizer A Outlet Temperature Sensor Circuit High Likely for this code High
- P2A54 Alternative Fuel Vaporizer A Outlet Temperature Sensor Circuit Intermittent/Erratic Likely for this code High
- P2A55 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit Likely for this code High
- P2A56 Alternative Fuel Vaporizer B Outlet Temperature Sensor Range/Performance Likely for this code High
- P2A57 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit Low Likely for this code High
- P2A58 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit High Likely for this code High
- P2A59 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit Intermittent/Erratic Likely for this code High
- P2A5A Alternative Fuel Vaporizer C Outlet Temperature Sensor Circuit Likely for this code High
- P2A5B Alternative Fuel Vaporizer C Outlet Temperature Sensor Range/Performance Likely for this code High
- P2A5C Alternative Fuel Vaporizer C Outlet Temperature Sensor Circuit Low Likely for this code High
- P2A5D Alternative Fuel Vaporizer C Outlet Temperature Sensor Circuit High Likely for this code High
- P2A5E Alternative Fuel Vaporizer C Outlet Temperature Sensor Circuit Intermittent/Erratic Likely for this code High
- P2A8B Alternative Fuel Vaporizer A Performance Likely for this code High
- P2A8C Alternative Fuel Vaporizer B Performance Likely for this code High
- P2A8D Alternative Fuel Vaporizer C Performance Likely for this code High
Information, not instruction
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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.
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