What it means
Closed-loop fuel trim hit its lean correction limit because mixture is structurally too rich. Likely fuel pressure too high, leaking injector, or O2 sensor reporting too lean.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
In closed-loop air/fuel control, the module compares oxygen or air/fuel sensor feedback with its target and adjusts fuel delivery. P016B sets when the system reaches its correction limit while trying to reduce fuel because the mixture remains too rich.
Common causes
Most likely first.
- Fuel pressure too high
- Fuel injector leaking
- Fuel pressure regulator malfunction
- Air/fuel sensor or oxygen sensor reporting incorrectly
- Purge valve allowing excess fuel vapor into the intake
Symptoms
- Check engine light on
- Increased fuel consumption
- Black smoke from exhaust on acceleration
- Smell of unburned fuel, fouled spark plugs
How to diagnose it
- Read freeze-frame data and compare short- and long-term fuel trims with oxygen or air/fuel sensor readings to confirm that the module is removing fuel.
- Check whether the rich correction occurs at idle, under load, or across operating conditions, since that helps distinguish purge flow, fuel delivery, and sensor issues.
- Inspect the air intake, exhaust sensor wiring, and purge valve connections for damage or leaks that could distort readings or admit excess vapor.
- Check fuel pressure and regulator operation against the manufacturer's specification.
- Check for a leaking injector and verify that the air/fuel or oxygen sensor responds plausibly before replacing it.
Common fixes
- Repair a purge valve that is allowing excess fuel vapor into the intake.
- Replace a confirmed leaking fuel injector.
- Repair or replace a fuel pressure regulator or control component that is causing excessive pressure.
- Repair sensor wiring or replace an air/fuel or oxygen sensor only if its signal fails testing.
Can I keep driving?
Avoid driving if there is heavy fuel odor, black smoke, rough running, or a flashing check engine light; unburned fuel can damage the catalytic converter. If symptoms are mild, drive only gently and get the rich condition diagnosed soon.
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.