What it means
Closed-loop fuel trim hit its rich correction limit because mixture is structurally too lean. Likely vacuum leak, low fuel pressure, or contaminated MAF.
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 uses oxygen or air/fuel sensor feedback to correct the mixture. P016C sets when it reaches its correction limit while adding fuel because the mixture remains too lean.
Common causes
Most likely first.
- Vacuum or intake air leak
- Fuel pressure too low
- Restricted fuel supply
- Mass air flow sensor contaminated or inaccurate
- Air/fuel sensor or oxygen sensor reporting incorrectly
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
How to diagnose it
- Read freeze-frame data and fuel trims to confirm that the module is adding fuel, and note whether the high correction occurs at idle or under load.
- Inspect intake hoses, vacuum lines, and the intake manifold area for leaks that can admit unmetered air.
- Check the air filter and inspect the mass air flow sensor and its wiring for contamination, damage, or poor connection.
- Measure fuel pressure and check for supply restrictions against the manufacturer's specification.
- Check the oxygen or air/fuel sensor response and wiring to rule out a falsely lean signal before replacing parts.
Common fixes
- Repair a cracked intake hose, vacuum line, or confirmed intake gasket leak.
- Replace a restricted air filter or clean the mass air flow sensor using an appropriate method.
- Repair a restricted fuel supply or a weak fuel pump confirmed by pressure testing.
- Repair sensor wiring or replace an oxygen or air/fuel sensor only if testing confirms a faulty signal.
Can I keep driving?
Avoid heavy acceleration, towing, and long trips if the engine hesitates, stalls, or loses power; a lean mixture can cause poor running and excessive engine heat. Stop driving if stalling makes the vehicle unsafe.
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.