Damaged wiring to the cylinder 4 injector, such as chafed insulation shorting the control wire to a voltage supply; Corroded, loose or damaged injector connector or terminals; Faulty cylinder 4 injector with an internal electrical fault; Open or poor connection in the injector circuit causing a high voltage reading; Fault in the engine control unit injector driver; Wiring harness damage from heat, vibration or previous repair work.

P0271

Cylinder 4 Injector A Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
71: FaultThe specific fault in that area

What it means

P0271 is the generic code for a high voltage condition in the control circuit of the cylinder 4 fuel injector. The engine control unit monitors the injector driver circuit and has detected a voltage or signal state higher than expected, which usually points to a short to voltage or a fault in the driver or wiring. The exact circuit layout and the meaning of 'A' depend on the engine and fuel system, so check the manufacturer data for the vehicle.

Symptoms

Engine misfire or rough running, mainly on cylinder 4
Malfunction indicator lamp on
Hesitation or loss of power
Poor fuel economy
Hard starting or a stall at idle
Fuel smell or raised exhaust emissions

Possible causes

Damaged wiring to the cylinder 4 injector, such as chafed insulation shorting the control wire to a voltage supplylikely
Corroded, loose or damaged injector connector or terminalslikely
Faulty cylinder 4 injector with an internal electrical faultlikely
Open or poor connection in the injector circuit causing a high voltage readingpossible
Fault in the engine control unit injector driverrare
Wiring harness damage from heat, vibration or previous repair workpossible

How to diagnose

Read all stored and pending codes and note the freeze frame data, including engine load, temperature and rpm when the fault set
Check for other injector or misfire codes on different cylinders, which may point to a shared supply or control unit fault
Visually inspect the cylinder 4 injector connector and the harness along its route for chafing, heat damage, corrosion or bent pins
Check the connector terminals for tightness and contamination, and repair as needed before further testing
Measure the injector coil resistance and compare it with the manufacturer specification
With the connector unplugged, test the control wire for a short to voltage and for continuity to the control unit, using the wiring diagram for that engine
Check the injector supply voltage and the earth or driver signal while the engine is cranked, following the manufacturer procedure
Swap the injector with another cylinder only if the manufacturer allows it and see whether the fault follows

How to fix

Repair or replace the damaged section of wiring and secure it clear of heat and sharp edges
Clean or replace the injector connector and terminals
Replace the cylinder 4 injector if its resistance or operation is out of specification, and carry out any required coding or adaptation for that engine
Repair the open circuit or poor connection found during testing
Replace or repair the engine control unit only after the wiring and injector are confirmed good and the manufacturer procedure points to a driver fault

Can I keep driving?

Medium severity

The car may be drivable for a short time, but the cylinder may not fire properly, which can overload the catalytic converter with unburnt fuel. Have it fixed soon, and avoid heavy loads or long journeys until then.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.