U3031
Ignition Output Off.
- Generic
- Network
- Generic code
- Medium severity
How this code is built
- U
- SystemNetwork
- 3
- Defined bySAE, the same on every car
- 0
- AreaNetwork area 0
- 31
- FaultThe specific fault in that area
What it means
U3031 is listed generically as 'Ignition Output Off'. A control module has logged that an ignition-related output or ignition-on signal was off when it should have been on, or did not match what was commanded. U3xxx codes are largely left to the manufacturer, so the exact trigger, and which module sets it, depends on the make, model and engine.
Symptoms
- Engine cranks but will not start, or starts and then stalls
- Intermittent loss of power or cutting out while driving
- Warning lights on the dashboard, such as engine or multiple system lights
- Misfire or rough running
- Other modules reporting communication or low voltage faults
- Intermittent no-start that comes and goes with no pattern
Possible causes
- Low or unstable battery voltage, or poor battery terminal connectionslikely
- Wiring or connector fault in the ignition feed, switched supply or ignition output circuit (open circuit, high resistance, short)likely
- Blown fuse or faulty relay in the ignition or engine management supplypossible
- Worn or faulty ignition switch, or a start/stop or keyless system faultpossible
- Poor earth connection to the engine control unit or body control modulepossible
- Internal fault in the engine control unit, body control module or ignition driverrare
- Network communication fault between modules affecting the ignition status messagerare
How to diagnose
- Read all stored codes and freeze frame data, noting whether the code is current or history and any related voltage or network codes.
- Test battery state of charge and voltage while cranking and with the engine running, and check the charging system output.
- Inspect battery terminals, main earths and the relevant fuses and relays for corrosion, looseness or damage.
- Inspect the wiring and connectors at the ignition switch, body control module and engine control unit for chafing, water ingress or pushed-out pins.
- With the ignition on, check the switched ignition supply at the module and carry out voltage drop tests on the supply and earth circuits.
- Watch live data for ignition status and supply voltage while wiggling the harness and operating the key to find intermittent faults.
- Check for network faults by looking for other communication codes and checking the bus wiring, following the manufacturer's procedure for the model.
- Check for manufacturer service information or software updates relating to this code on the specific vehicle before condemning a module.
How to fix
- Charge or replace a weak battery and clean and tighten the terminals and earths.
- Repair or replace damaged wiring, terminals or connectors in the ignition supply or output circuit.
- Replace any failed fuse or relay only after finding and fixing the cause of the failure.
- Replace a worn ignition switch or repair the keyless or start/stop system fault.
- Repair or replace the faulty control module only once supply, earth and network faults are ruled out, then carry out any programming the manufacturer requires.
- Apply a manufacturer software update only if service information lists it as a fix for this fault.
Can I keep driving?
Medium severity
The car may cut out or fail to restart, so fix it soon. If the engine is cutting out while driving, avoid driving it because losing power in traffic is unsafe.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.