P0291 – Cylinder 11 Injector Circuit Low

P0291 is an OBD-II trouble code that points to a problem with the fuel injector circuit on cylinder 11. While not as common as misfire or oxygen sensor codes, it can cause rough running, poor fuel economy, and long-term engine damage if ignored. You’ll usually feel a loss of power or a rough idle, especially under load. In this guide, you’ll learn exactly what P0291 means, the most likely causes, the symptoms to watch for, how a mechanic diagnoses it, and what repairs typically cost.

What Does P0291 Mean?

P0291 stands for “Cylinder 11 Injector Circuit Low.” Your engine control unit (ECU) monitors the voltage and current going to each fuel injector. When it sees that the signal for injector number 11 is consistently lower than expected, it sets this code and turns on the check engine light.

“Circuit low” usually means the ECU is seeing low voltage, excessive resistance, or a short-to-ground in the injector circuit. It can be caused by a bad injector, damaged wiring, poor connections, or in rare cases a failing ECU driver. On engines with 12 cylinders, cylinder 11 is typically on the second bank near the rear, which can make access tight.

Quick Reference

• Code: P0291
• Definition: Cylinder 11 Injector Circuit Low
• System: Fuel injection / engine management
• Severity: Moderate to high – drivability and potential engine damage
• Common Fixes: Injector replacement, wiring repair, connector cleaning, ECU driver testing

Real-World Example / Field Notes

I’ve seen P0291 most often on high-mileage V12 luxury cars and heavy-duty trucks that spend a lot of time idling or towing. One example: a customer with a V12 sedan came in complaining of a rough idle and poor fuel economy. Scan data showed P0291 and a slight misfire on cylinder 11. The injector looked fine from the outside, but a resistance check showed it was out of spec. Replacing the injector and cleaning the connector terminals cleared the code and restored smooth operation. In many cases, the wiring near the rear cylinders gets brittle from heat, so a careful visual inspection is critical.

Symptoms of P0291

• Check engine light on – P0291 will usually store as a confirmed code and illuminate the MIL.
• Rough idle – The engine may shake or feel uneven, especially at stoplights.
• Loss of power – You may notice sluggish acceleration or poor performance under load.
• Engine misfire – A noticeable stumble or hesitation, sometimes more obvious when cold.
• Poor fuel economy – The ECU may overcompensate with other cylinders, increasing fuel use.
• Fuel smell from exhaust – Unburned fuel due to incomplete combustion on cylinder 11.
• Hard starting – Extended cranking or needing to press the throttle to start in severe cases.
• Possible limp mode – Some vehicles reduce power to protect the engine and catalytic converters.

Common Causes of P0291

Most Common Causes

• Faulty fuel injector (cylinder 11) – Internal coil failure, sticking pintle, or open/shorted windings will cause low circuit voltage or abnormal current draw.
• Damaged injector wiring – Chafed, melted, or broken wires between the injector and ECU are a leading cause, especially near hot exhaust components.
• Corroded or loose injector connector – Moisture, oil, or vibration can cause poor contact and a “low” signal at the ECU.
• Poor ground or power supply – Shared grounds or power feeds for multiple injectors can fail, affecting one cylinder more than others.
• Previous engine work – Harnesses not clipped back correctly after repairs can rub through over time.

Less Common Causes

• ECU driver failure – The internal injector driver for cylinder 11 can fail, causing a low signal even with a good injector and wiring.
• Connector pin damage at ECU – Bent, backed-out, or corroded pins at the ECU plug can drop voltage.
• Aftermarket modifications – Poorly installed performance injectors, piggyback tuners, or remote start systems can interfere with injector circuits.
• Low system voltage – Weak battery or charging issues can aggravate marginal injector circuits and trigger P0291.
• Internal engine issues – Rarely, severe mechanical problems on cylinder 11 can confuse diagnostics, though they usually trigger misfire codes first.

Diagnosis: Step-by-Step Guide

You’ll want a basic scan tool, a digital multimeter (DMM), and ideally a noid light or lab scope. Access to wiring diagrams and service information for your specific vehicle is a big help. If you’re comfortable with electrical testing, you can do the preliminary checks yourself before deciding on repairs.

1. Confirm the code and check for others. Scan the ECU for P0291 and any related codes (misfires, other injector codes, low voltage). Freeze frame data will show when the fault occurred.
2. Visual inspection of cylinder 11 area. Locate cylinder 11 and inspect the injector, connector, and harness. Look for broken clips, melted insulation, oil saturation, or obvious damage.
3. Wiggle test the harness. With the engine idling, gently move the injector wiring. If the idle changes or the engine stumbles, you likely have an intermittent wiring or connector issue.
4. Check injector resistance. Key off, unplug the injector for cylinder 11, and measure resistance across the injector terminals. Compare to spec and to a known good injector. Out-of-range resistance usually means a bad injector.
5. Verify power and ground at the injector. With key on, use a DMM or test light to confirm proper voltage supply and ground at the injector connector. One side is usually battery voltage, the other is ECU-controlled ground.
6. Use a noid light or scope. Plug a noid light into the injector connector or back-probe with a scope. Crank or run the engine to see if the ECU is sending a proper pulse. No or weak pulse points to wiring or ECU driver issues.
7. Check continuity from injector to ECU. If power/ground look good, test continuity and resistance of the signal wire(s) between the injector and ECU connector. Repair any open circuits, shorts to ground, or shorts to other wires.
8. Swap components if possible. On some engines, you can swap injector 11 with another cylinder. If the code follows the injector (for example, becomes P0288 or P0289), the injector is at fault.
9. Inspect ECU and connectors. If wiring and injector test good, inspect the ECU connector pins for corrosion or damage. In rare cases, an internal ECU fault will require replacement and programming.
10. Clear codes and road test. After repairs, clear codes, monitor live data, and perform a road test under similar conditions to the freeze frame to confirm the fix.

Pro tip: Use Mode $06 data (if your scan tool supports it) to look at injector or misfire counters. This can help confirm that cylinder 11 was truly the problem and that it’s not just a random, intermittent glitch.

Possible Fixes & Repair Costs

Repairs for P0291 depend on whether the issue is the injector itself, the wiring, or the ECU. A typical fuel injector replacement on a V12 engine can range from $200 to $600 for parts and labor, depending on access and brand. Wiring repairs, such as fixing a broken or shorted wire, usually run $100 to $300. If the ECU needs replacement or repair, costs can jump to $600–$1,500 including programming. Labor rates, vehicle make, and how buried cylinder 11 is under intake components all affect the final bill.

• Replace cylinder 11 injector – When resistance or swap testing proves the injector faulty.
• Repair or replace damaged wiring – Fix chafed, melted, or broken wires and secure the harness properly.
• Clean or replace injector connector – Address corrosion, bent pins, or poor terminal tension.
• Repair shared power/ground issues – Restore proper voltage supply to the injector bank.
• ECU repair or replacement – Only after confirming all external components are good.

Can I Still Drive With P0291?

You can usually drive short distances with P0291, but it’s not something you want to ignore. A weak or non-functioning injector on cylinder 11 means that cylinder isn’t burning fuel correctly. This can cause rough running, poor fuel economy, and higher emissions. In some cases, raw fuel can reach the catalytic converter and overheat it. If the engine is shaking badly, going into limp mode, or the check engine light is flashing, you should avoid driving and have the vehicle towed to a shop.

What Happens If You Ignore P0291?

Ignoring P0291 can lead to accelerated wear on the engine and exhaust system. A consistently lean or misfiring cylinder can damage pistons, valves, and spark plugs, and unburned fuel can overheat and destroy catalytic converters, turning a moderate repair into a very expensive one. You’ll also live with poor drivability and higher fuel costs, so it’s worth fixing sooner rather than later.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0291

P0291 is most common on engines with 11 or more cylinders, so you’ll see it primarily on V12 luxury cars and heavy-duty applications. Manufacturers where this code shows up more often include Mercedes-Benz, BMW, Audi, Jaguar, Land Rover, and some high-end performance brands with V12 engines. It can also appear on certain diesel trucks and commercial vehicles that use multi-cylinder injection systems. Age, high mileage, heat, and tight engine bays all contribute to injector wiring and connector problems on these vehicles.