OBD-II Code P0275 — What It Means & How to Fix It

What Does This Error Mean?

P0275 means Cylinder 5 is not contributing its expected share of engine power — a cylinder contribution or balance fault. The engine computer watches for tiny changes in crankshaft speed after each cylinder fires. If Cylinder 5 doesn't cause the expected speed bump, the ECM flags it as underperforming. This is different from a full misfire — the cylinder is firing, just weakly. Expect symptoms like a subtle engine vibration, rough idle, slightly reduced power, and modestly worse fuel economy.

Affected Models

All vehicles 1996+ with 5 or more cylinders
Common in GM V6 and V8 engines
Common in Ford V8 and V10 engines
Common in high-mileage vehicles with neglected maintenance

Common Causes

Worn or fouled spark plug on Cylinder 5 causing weak combustion
Failing ignition coil on Cylinder 5 producing insufficient spark
Partially clogged Cylinder 5 fuel injector delivering less fuel than needed
Low compression on Cylinder 5 from worn rings, valves, or a head gasket problem
Small vacuum leak near the Cylinder 5 intake port creating a lean condition in that cylinder

How to Fix It

Remove and inspect the Cylinder 5 spark plug. A plug that looks significantly worse than the others — burnt, oil-fouled, or heavily gapped — is likely the cause of the underperformance. Replace the full set of plugs if they're near service life.

Cylinder 5 on many V6 and V8 engines sits on the rear bank and can be harder to access, meaning it often goes longer without service than front-bank cylinders.
Swap the Cylinder 5 ignition coil with a coil from a neighboring cylinder. Clear the code, drive, and see if the contribution fault moves to the new cylinder location. If it does, the Cylinder 5 coil is faulty. Replace it.

Coil swap testing is a reliable, free diagnostic step that avoids guesswork.
Have the Cylinder 5 injector flow-tested at a shop. A partially restricted injector delivers fuel — just not enough for full combustion. Ultrasonic cleaning can often restore flow to a clogged injector at a fraction of replacement cost.

Ask specifically for a flow-rate test, not just an electrical resistance test. A clogged injector can pass the resistance test while still flowing poorly.
Check for vacuum leaks around the Cylinder 5 intake runner. Use a smoke machine (available at many shops) or spray carburetor cleaner carefully at idle near intake manifold joints and vacuum hose connections. RPM changes indicate a leak.

A vacuum leak at one runner creates a lean condition in just that cylinder, causing it to produce less power without fully misfiring.
Perform a compression test on all cylinders and compare readings. All cylinders should be within 10% of the highest reading. Low compression on Cylinder 5 means internal engine wear that no tune-up will resolve — professional evaluation is required.

Follow a low compression finding with a cylinder leak-down test to determine whether the cause is rings, valves, or a head gasket.

When to Call a Professional

If spark plug and coil replacement don't resolve the fault, ask a mechanic to perform a compression test and leak-down test on Cylinder 5. Low compression requires professional evaluation — it can mean worn rings, damaged valves, or a blown head gasket. Ignoring a contribution fault risks it progressing into a full misfire, which can damage the catalytic converter.

Frequently Asked Questions

Is P0275 serious?

It's a warning you should take seriously but not panic about. Cylinder 5 is running weak, not dead. If you fix it promptly — often just a spark plug or coil — the repair is inexpensive. Ignoring it risks a full misfire and catalytic converter damage, which costs a lot more.

Why would only Cylinder 5 have this problem?

Every cylinder experiences the same wear factors, but Cylinder 5 can be first to show it for several reasons. On rear-bank cylinders it's harder to access for service, so maintenance gets deferred. Or that injector or coil simply wore out first — parts fail at different rates.

How much does it cost to fix P0275?

Spark plug set: $50–$150 installed. Ignition coil: $50–$200 installed. Injector cleaning: $50–$100. Injector replacement: $150–$400. Engine internal repairs: $1,000–$4,000+.