P0291
Cylinder 11 Injector A Circuit Low.
- 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)
- 91
- FaultThe specific fault in that area
What it means
P0291 means the engine control unit has detected a low voltage or current fault in the control circuit of the cylinder 11 injector (circuit A). The unit monitors the injector driver and wiring, and saw a reading lower than expected, which points to a short to ground, a very low resistance or a fault in the driver. Cylinder 11 only exists on large engines (typically V12), and the cylinder numbering and injector layout depend on the manufacturer and engine.
Symptoms
- Engine management light on
- Misfire or rough running, especially at idle
- Loss of power or poor acceleration
- Raised fuel consumption or a smell of fuel
- Hard starting or an engine running on fewer cylinders
- Possible limp mode on some models
Possible causes
- Cylinder 11 injector with an internal short or low coil resistancelikely
- Injector wiring chafed or shorted to ground between the injector and the control unitlikely
- Corroded, damaged or water-contaminated injector connector or harness plugpossible
- Fault in the shared supply feed or wiring to the injector bank, giving a low readingpossible
- Faulty injector driver circuit inside the engine control unit or a separate driver modulerare
- Outdated control unit software where a manufacturer bulletin covers false injector circuit faultsrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data (engine speed, load, temperature, battery voltage), and check for other injector or misfire codes.
- Confirm which physical cylinder is cylinder 11 for this engine using the manufacturer's data, as numbering and bank layout vary.
- Visually inspect the injector connector, harness routing and nearby wiring for chafing, heat damage, oil contamination, corrosion or water ingress.
- With the ignition off and connector unplugged, measure the injector coil resistance and compare it with the manufacturer's specification.
- Test the injector control wire and supply wire for continuity and for any short to ground or to other wires.
- Check the injector supply voltage and fuses or relays feeding the circuit with the ignition on.
- Where permitted, swap the injector or its connector with another cylinder, clear the code and see whether the fault follows.
- Check the injector signal with an oscilloscope, and look for a software update or technical bulletin for the engine if the wiring and injector test good.
How to fix
- Replace the cylinder 11 injector if its resistance or waveform is out of specification, following the manufacturer's procedure for seals and any coding.
- Repair or replace damaged wiring that is shorted to ground, using proper soldered and sealed repairs.
- Clean, repair or replace a corroded or damaged connector and its terminals.
- Repair the supply feed, fuse or relay fault found in the injector supply circuit.
- Repair or replace the control unit or driver module only after the wiring and injector are proven good.
- Apply an updated control unit calibration if the manufacturer lists an outdated one as the known cause.
Can I keep driving?
Drive only gently and as little as possible until it is repaired, as a dead or misfiring cylinder can wash fuel into the exhaust and damage the catalytic converters. If the engine light flashes, or the engine runs badly or goes into limp mode, stop and have it checked.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.