P0275

What P0275 Means

Code P0275 points to a power imbalance in cylinder 5. It belongs to the cylinder contribution/balance family of codes, which flag uneven contribution from a single cylinder to total engine output. The engine management system (DME) evaluates each cylinder's work from the crankshaft position sensor signal and, in some cases, oxygen sensor data, comparing crankshaft acceleration on the power stroke.

When cylinder 5's contribution falls below the expected value, the DME sets P0275. The cause can be insufficient fuel delivery (a faulty fuel injector), wiring or connector problems at the injector, or mechanical factors affecting compression or valvetrain operation. The code falls under the fuel_injection category and is moderately critical: it doesn't require an immediate shutdown, but ignoring it can lead to further damage.

Symptoms

• Misfires — most noticeable at idle or under load.
• Rough idle — the engine may vibrate and the rpm may fluctuate.
• Loss of power — reduced pull, especially during acceleration.
• Check Engine light — comes on in the instrument cluster.

Diagnosis and Repair

1. Check the cylinder 5 injector — use diagnostic equipment (ISTA, INPA) to evaluate injector operation, check its resistance and flow. A bench test is also an option.
2. Inspect the wiring and connectors — check the integrity of the harness running to the cylinder 5 injector for corrosion, damaged insulation, and a secure connector contact.
3. Replace the injector if needed — if the injector is faulty (clogged, leaking, or out of resistance spec), replace it. Use genuine BMW parts or quality equivalents that meet the engine specification.

Recommended tools: ISTA or INPA diagnostic software, a multimeter for checking electrical circuits.

Secondary Problems

Running with P0275 for a long time can lead to the following:

• Increased catalytic converter wear — unburned fuel from the dead cylinder reaches the exhaust and damages the catalytic converter.
• Spark plug damage — with the wrong mixture, the plug can foul or fail.
• Worse fuel economy and higher emissions — from inefficient combustion.
• Risk of engine damage — prolonged misfires can dilute the oil with fuel and accelerate cylinder and piston wear.

Don't put the repair off, since ignoring the fault can lead to more expensive breakdowns.