Fuel and air

P0291 — Cylinder 11 Injector Circuit Low

Severity: medium Drive with care, to a shop

What P0291 means

The engine control unit fires the cylinder 11 injector by switching its circuit to ground and monitors the voltage in that circuit. P0291 sets when that voltage is lower than expected, for example from a short to ground, a failed injector coil or a faulty driver in the control unit. Only engines with many cylinders (such as V12s) have a cylinder 11, so this code is uncommon.

Symptoms

  • Check engine light on
  • Rough running or vibration
  • Reduced engine power
  • Worse fuel economy
  • Misfire on one cylinder
  • Hard starting or unstable idle

Possible causes

  1. Failed cylinder 11 fuel injector (shorted coil)
  2. Open circuit or short to ground in the injector harness
  3. Loose or corroded injector connector
  4. Chafed or damaged wire insulation
  5. Faulty injector driver inside the PCM (rare)

How to diagnose

  1. Read all codes and freeze frame data and look for related misfire codes
  2. Inspect the cylinder 11 injector connector and harness for corrosion, chafing and poor contact
  3. Measure injector coil resistance and compare with the spec for that engine
  4. Test the circuit for a short to ground and for opens with the PCM connector unplugged
  5. Check power supply and the control signal at the injector with a test light or scope
  6. Swap the injector with a neighboring one and see if the code follows
  7. Check fuel pressure and fuel trim values
  8. If wiring and injector test good, evaluate the PCM

Common fixes

  • Repair or replace the damaged injector harness or connector
  • Replace the faulty cylinder 11 injector
  • Clean the connector terminals and remove corrosion
  • Repair or replace the PCM if the driver is confirmed faulty

Questions and answers

What does P0291 mean?

It means low voltage in the control circuit of the cylinder 11 fuel injector. The injector itself or its wiring and connector are the usual culprits.

Can I drive with code P0291?

Short trips are usually possible, but expect rough running and higher fuel use. Do not put off the diagnosis, as unburned fuel can harm the catalytic converter.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.