What does it mean?
P1231 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Fuel Pump Relay Control Circuit High Voltage .
Symptoms
- No fuel pump prime and a crank but no start condition
- Engine stalls and will not restart, sometimes intermittently
- Sudden cut-out while driving, then a normal restart later
- Check engine lamp on, often with fuel pressure or lean codes
- Fuel pump running continuously if the circuit is being fed from elsewhere
Likely causes
- Open control wire between the module and the relay
- Open relay coil, or a relay that has been removed or fitted in the wrong socket
- Corroded, burnt or spread terminals in the relay socket
- Control wire shorted to battery voltage from harness chafe
- Poor relay coil ground or a corroded ground point
- Failed low side driver inside the control module
- Water damage in the fuse and relay box
How to fix it
- Command the fuel pump relay with the scan tool and listen for it to click
- Swap in a known good identical relay as a quick check and verify the socket layout
- Measure voltage on the control terminal with the ignition on and again while the relay is commanded
- Test the coil circuit for continuity from the relay socket to the module connector
- Inspect the socket and box for corrosion, heat discolouration and water
- Check for a short to battery on the control wire with the relay and module unplugged
- Repair the wiring, then verify pump prime and fuel pressure before considering the module driver