What it means
ECU took longer than allowed to enter closed-loop air/fuel ratio control. Most often O2 sensor heater aging or coolant temperature reading wrong.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine control module uses oxygen or air/fuel sensor feedback to adjust fueling once the engine enters closed-loop control. P016A sets when that transition takes longer than the calibrated allowance, often because a sensor heater or engine warm-up input delays usable feedback.
Common causes
Most likely first.
- Oxygen sensor or air/fuel sensor heater aged or failing
- Coolant temperature sensor reading incorrectly
- Damaged wiring or poor connector contact
- Engine taking unusually long to warm up
How to diagnose it
- Check freeze-frame data and startup live data to see how long the engine took to reach closed loop and whether the coolant temperature reading was plausible before starting.
- Watch coolant temperature rise from a cold start and compare it with ambient temperature and the engine's warm-up behavior.
- Check scan data for the oxygen or air/fuel sensor's readiness and response during warm-up.
- Inspect the relevant sensor heater wiring and connectors for damage, corrosion, or loose contact.
- Test the sensor heater circuit and coolant temperature sensor against the manufacturer's specification, then investigate slow engine warm-up if readings are sound.
Common fixes
- Repair damaged wiring or poor contact at the affected sensor or heater connector.
- Replace a coolant temperature sensor that reads implausibly or fails testing.
- Replace an oxygen or air/fuel sensor whose heater or warm-up response fails testing.
- Repair a confirmed engine warm-up problem that keeps the engine from reaching operating temperature normally.
Can I keep driving?
If the engine starts and runs normally, you can usually drive gently, but avoid unnecessary short trips because delayed closed-loop operation can increase fuel use and emissions. Seek prompt diagnosis if it begins running poorly or the warning light flashes.
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.