P0294

What it means

P0294 means the engine control unit has detected a low voltage or low signal in the injector A control circuit for cylinder 12. The unit monitors the injector driver and circuit, and the voltage or current was lower than expected, which points to a short to earth, a shorted injector winding or a driver fault. The code only applies to engines with at least 12 cylinders, and how the cylinders are numbered and where the injector sits depends on the engine.

Symptoms

• Engine warning light on
• Rough running or misfire on cylinder 12, especially at idle
• Hesitation or loss of power
• Poor fuel economy or a fuel smell from the exhaust
• Hard starting or an engine that runs on fewer cylinders
• Engine in limp mode on some vehicles

Possible causes

• Injector for cylinder 12 with a shorted or low-resistance internal windinglikely
• Injector wiring chafed or shorted to earth between the injector and the control unitlikely
• Corroded, loose or damaged injector connector or terminalslikely
• Water or oil contamination in the connector or harnesspossible
• Fault in the injector driver circuit inside the engine control unitrare
• Harness damaged by heat or rubbing near the cylinder bank for cylinder 12possible

How to diagnose

1. Read all stored and pending codes and the freeze frame data, and note whether other injector or misfire codes are present for cylinder 12 or neighbouring cylinders.
2. Check for technical service bulletins or known issues for the specific engine, as injector and harness faults vary by model.
3. Visually inspect the cylinder 12 injector connector and the harness for chafing, heat damage, corrosion, moisture and bent or pushed-back pins.
4. With the ignition off and the connector unplugged, measure the injector winding resistance and compare it with the manufacturer specification for that engine.
5. Check the injector wiring for a short to earth and for continuity from the injector connector to the control unit connector, following the wiring diagram.
6. Check the supply voltage and the control signal at the connector with a suitable meter or oscilloscope while cranking.
7. Swap the injector with one from another cylinder if the engine design allows it, clear the code and see whether the fault follows the injector.
8. If the injector and wiring are proved good, have the control unit driver circuit tested and check for any available software update.

How to fix

• Replace the faulty cylinder 12 injector and fit new seals as the manufacturer specifies.
• Repair or replace the damaged section of harness, using proper soldered or sealed repairs.
• Clean or replace the corroded connector or terminals and make sure it is fully locked.
• Dry out and seal the connector or fix the source of water or oil ingress.
• Repair or replace the engine control unit only after all other causes have been ruled out, and update the calibration if an outdated one is a known cause.

Can I keep driving?

Nearby codes

• P0293GenericCylinder 11 Contribution/Balance
• P0295GenericCylinder 12 Injector A Circuit High