What it means
During cylinder deactivation on bank 1, the fuel trim of the active cylinders runs persistently lean. Indicates unmetered air ingress or fuel delivery shortfall.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Cylinder deactivation temporarily shuts off selected cylinders, leaving the others to keep the engine running. The control module monitors fuel-trim feedback from bank 1 while deactivation is active. This code sets when the active cylinders on bank 1 need persistently more fuel than expected, indicating a lean condition such as unmetered air or insufficient fuel pressure.
Common causes
Most likely first.
- Vacuum leak unmasked during deactivation
- 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 use live data to compare bank 1 fuel trims during normal operation and cylinder deactivation.
- Check for related misfire or air-fuel sensor codes and note whether roughness or stalling occurs specifically when deactivation begins.
- Inspect bank 1 intake and vacuum hoses for leaks that may become more influential when cylinders deactivate.
- Check fuel pressure under the conditions specified by the manufacturer, since low rail pressure can lean the active cylinders.
- If air leaks and fuel pressure check out, evaluate bank 1 sensor readings and injector delivery using the manufacturer's procedures.
Common fixes
- Repair a vacuum or intake leak affecting bank 1.
- Replace a cracked or disconnected hose causing unmetered air entry.
- Correct low fuel pressure after identifying the failing fuel-delivery component.
- Repair a bank 1 sensor or injector fault confirmed by testing.
Can I keep driving?
Because this fault can cause rough running, hesitation, or stalling, avoid high-speed driving, heavy loads, and situations where a stall would be dangerous. Continued lean operation can worsen drivability and may damage the engine or exhaust components.
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.