P0291 Code Meaning and Next Steps

First checks take 10 to 20 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine starts misfiring badly, stalling, or losing power sharply.
!The check-engine light flashes or the vehicle runs rough enough to risk catalyst damage.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but it should not be ignored.

What to check first

Step-by-step checks

1
Free - no tools
Check whether P0291 appears with misfire or fuel-trim codes
2
Free - no tools
Inspect the injector and ignition connectors on cylinder 11 for looseness or damage
3
Basic tool needed
Compare scan data for cylinder contribution across nearby cylinders
4
Basic tool needed
Notice whether the problem is worse at idle or under load
5
Basic tool needed
If the engine has a known mechanical issue, treat it as a primary clue

If the code returns

-If ignition swap tests move the fault, focus on ignition parts first.
-If injector testing points to fuel delivery trouble, focus there before buying more parts.
-If the code returns after repair, repeat the balance check before assuming another cylinder is at fault.

Background

What this code means

P0291 is a generic OBD-II code for cylinder 11 contribution or balance fault.

That usually means the ECU sees cylinder 11 as weaker than the rest of the engine during its balance check.

Diagnosis

Common causes

Most common

Weak spark on cylinder 11

A plug, coil, or wire issue can reduce that cylinder's output.

Common

Injector imbalance

A weak or restricted injector can make the cylinder contribute less than the others.

Common

Compression problem

A mechanical issue can keep the cylinder from making normal power.

Possible

Connector or wiring fault

A poor connection can interrupt the injector or ignition circuit.

Avoid these mistakes

What not to do

xDo not replace injectors as a set before checking for wiring, fuel pressure, or a mechanical cylinder issue.
xDo not ignore drivability changes just because the code sounds like an injector balance fault.

Parts

Parts that may need replacing

PartTypical costNotes

Spark plug or ignition coil$20-$150Relevant when ignition testing points to cylinder 11.

Fuel injector$50-$250Worth checking if the injector is weak or restricted.

Compression or leakdown test$0-$150Needed if the mechanical side looks weak.

Related OBD codes

P0287

P0287 usually means cylinder 11 contribution or balance is lower than expected.

P0300

P0300 usually means the engine is detecting random or multiple-cylinder misfires.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0291 was expanded around common cylinder 11 contribution faults, especially ignition weakness, injector imbalance, and compression problems.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0291 - P0291 Usually Means Cylinder 11 Contribution or Balance Is Low on Many Systems