What it means
Fuel control system A on bank 1 is reporting a lean condition. This indicates the system is correcting for a mixture that is leaner than its calibrated range.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Fuel control system A adjusts the air-fuel mixture for engine bank 1, the bank containing cylinder 1. The engine control module uses oxygen-sensor feedback and fuel-trim data to judge whether bank 1 is lean. This code sets when system A's correction indicates that bank 1 is leaner than the calibrated range.
Common causes
Most likely first.
- Vacuum leak downstream of MAF
- Fuel rail pressure low
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
How to diagnose it
- Record freeze-frame data and compare live fuel trims for bank 1 with bank 2 at idle and raised engine speed to see whether the lean correction is isolated to bank 1.
- Inspect the intake ducting and vacuum hoses downstream of the mass-airflow sensor for leaks that could admit unmetered air, especially near bank 1.
- Check for exhaust leaks ahead of the bank 1 oxygen sensor, which can make its feedback appear lean.
- If both banks show similar lean correction, measure fuel rail pressure and delivery against the manufacturer's specification because low fuel supply can affect both banks.
- If the lean correction is limited to bank 1, test its oxygen-sensor circuit and inspect bank 1 injectors and wiring before replacing parts.
Common fixes
- Repair a split vacuum hose or intake leak downstream of the mass-airflow sensor.
- Repair an exhaust leak ahead of the bank 1 oxygen sensor.
- Restore fuel pressure or delivery to the manufacturer's specification if testing confirms it is low.
- Repair a bank 1 injector or its wiring if testing identifies a fault.
Can I keep driving?
A short, gentle trip may be possible if the engine runs smoothly, but avoid hard acceleration and stop if it stalls or loses substantial power. A persistent lean mixture can cause poor running and may damage the catalytic converter.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.