P219A: Bank 1 Air-Fuel Ratio Imbalance

P219A means the engine computer has found that the cylinders on bank 1 (the side with cylinder 1, or the whole engine on a four-cylinder) are not all running at the same air-fuel ratio. Depending on the manufacturer, it spots this from ripples in the upstream air-fuel ratio sensor signal, from small changes in crankshaft speed, or both. The usual causes are a leaking or clogged injector, an intake leak at one runner, an ignition or compression problem on one cylinder, or a faulty upstream sensor.

P219A is a fuel system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P219A and illuminates the check engine light.

If your vehicle has triggered P219A, you may notice one or more of these symptoms:

• Check engine light on, often with no obvious change in how the car drives
• Slightly rough or uneven idle
• Hesitation or a faint stumble under light load
• Worse fuel economy
• Fuel smell from the exhaust when one cylinder runs rich
• Misfire codes stored alongside P219A

Here are the most common causes of P219A:

Generally yes, for short-term driving. Usually safe to drive gently to a workshop, but do not leave it for months. One cylinder running richer or leaner than the others raises emissions and fuel use, and if it develops into a misfire the unburned fuel can overheat the catalytic converter. If the check engine light starts flashing, the engine shakes or you smell raw fuel, stop driving and get it checked.

Follow these steps to pinpoint the root cause of P219A:

1. Read every stored code and the freeze frame. Some manufacturers store a second code that names the weak cylinder, and any misfire, fuel trim or air-fuel ratio sensor code stored with P219A narrows the search
2. Check the long-term fuel trims on a warm engine with a generic OBD2 reader. They show whether the bank as a whole is being corrected rich or lean, but not which cylinder is out of line
3. On many newer cars the Mode 06 test results include a misfire count for each cylinder. A cylinder with a count well above the others is the first suspect, even if no misfire code is stored
4. Check for intake leaks with a smoke test, paying attention to the gaskets and runners of individual cylinders, and look for exhaust leaks ahead of the upstream sensor
5. Inspect the spark plugs and check the ignition coils, swapping a suspect coil to another cylinder to see whether the fault follows it
6. Test the injectors. A workshop can use the manufacturer's tester to trim fuel to each cylinder in turn and watch the response, or flow and leak-test the injectors off the car; a generic reader cannot run these tests
7. If the injectors and ignition check out, run a compression test and inspect the intake valves for deposits, then check the upstream air-fuel ratio sensor and its wiring

Repair costs for P219A vary depending on the root cause and your vehicle. Here are typical estimates:

P219A behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

These codes are often seen alongside P219A or indicate related issues: