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DTC codes / P02xx · Fuel and air metering (injector circuits) / P0291

P0291Cylinder 11 Injector Circuit Low

P0291 indicates that the powertrain control module (PCM) has detected a low-voltage condition on the electrical circuit for cylinder 11's fuel injector. The PCM monitors the injector driver circuit and sets this code when the voltage on the control wire falls below the expected threshold, which typically means the circuit is shorted to ground or the injector's internal coil has failed.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering (injector circuits)

Symptoms you may notice

  • Illuminated check engine light (malfunction indicator lamp, MIL), often with no other noticeable symptoms
  • Rough idle or misfire, especially noticeable when the engine is cold or under light load
  • Reduced engine power and poor acceleration due to a dead cylinder
  • Shaking or vibration from the engine bay that worsens with load
  • A strong raw fuel smell from the exhaust if the injector is stuck open or not firing
  • Possible catalytic converter damage over time if unburned fuel reaches the exhaust

Common causes, most likely first

  1. Faulty fuel injector on cylinder 11 with an internally shorted coil
  2. Chafed or grounded injector control wire between the PCM and the injector
  3. Corroded or loose electrical connector at the cylinder 11 injector
  4. Damaged injector driver inside the PCM (less common but possible)
  5. Aftermarket alarm or remote start wiring that has tapped into the injector circuit
  6. Engine wiring harness damage from heat, rodents, or previous repairs

How to diagnose and fix it

  1. Inspect the cylinder 11 injector connector for corrosion, loose pins, or pushed-back terminals and clean or repair as needed
  2. Disconnect the injector and measure the resistance of the injector coil with a multimeter, comparing it to the manufacturer's specification
  3. Check the injector control wire for continuity to ground with the key off; a short to ground indicates a harness fault
  4. Wiggle-test the harness while watching live injector pulse-width data on a scan tool to catch intermittent shorts
  5. Swap the cylinder 11 injector with a known-good injector from another cylinder and see if the code follows the injector or stays with the cylinder
  6. If the harness and injector test good, check for a faulty PCM by verifying the driver circuit with a noid light or oscilloscope
  7. Replace the faulty injector or repair the harness, clear the code, and verify the repair with a road test and live data

Why cylinder 11 injector codes mislead

  • A low-voltage code on an injector circuit often comes from a shorted injector coil rather than a wiring problem, so resistance testing the injector is the fastest way to avoid unnecessary harness repairs.
  • Cylinder 11 is almost always on the second bank of a V12 or a high-count engine, and technicians sometimes overlook that the PCM may label cylinders differently than the physical layout, leading to testing the wrong injector.
  • Intermittent P0291 codes that appear only when the engine is hot often point to a failing injector coil that opens when hot, which will not show up on a cold resistance test.
  • A shorted injector driver inside the PCM can mimic a harness short, so always disconnect the PCM and recheck the circuit before condemning the computer.
  • Aftermarket remote starters or alarm systems that splice into injector wiring are a common hidden cause of low-voltage injector codes on vehicles with those accessories.

Can I keep driving with P0291?

You can drive short distances to a repair shop, but avoid heavy acceleration and long trips because a misfiring cylinder can overheat the catalytic converter and cause costly damage. If the check engine light is flashing, stop driving and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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