Emissions

P016A — Excessive time to enter closed loop air/fuel ratio control

Severity: medium Safe to drive

What P016A means

After a cold start the engine control module runs on preset fuel maps (open loop). Once the oxygen sensor is hot and ready, it switches to closed loop and trims fueling based on the sensor's signal. P016A sets when that switch takes longer than the programmed limit, usually because the sensor heats up or responds slowly, or because of a problem in its circuit.

Symptoms

  • Check Engine Light on
  • Worse fuel economy
  • Rough idle or hesitation
  • High emissions readings at a test
  • Slow warm-up at idle

Possible causes

  1. Aging or slow-responding oxygen sensor
  2. Failed oxygen sensor heater or its power circuit
  3. Exhaust leak near the sensor or an intake air leak
  4. Damaged wiring, corroded connector or poor ground in the sensor circuit
  5. Stuck-open thermostat or faulty coolant temperature sensor delaying warm-up
  6. Rarely, an ECM software issue

How to diagnose

  1. Scan for all codes and review freeze frame data, looking for related O2 sensor, heater or coolant temperature codes
  2. Confirm the engine warms up in a normal time and the coolant temperature reading is realistic
  3. Inspect the exhaust for cracks, bad gaskets and leaks upstream of the sensor
  4. Inspect the O2 sensor wiring and connector for chafing, moisture and corrosion
  5. Measure heater resistance and supply voltage at the sensor
  6. Watch live sensor data on a warm engine and check switching speed and amplitude
  7. After repair, clear the code and verify the system enters closed loop on time

Common fixes

  • Replace a slow or failed oxygen sensor
  • Repair exhaust leaks and replace bad gaskets
  • Repair wiring and connectors, clean contacts
  • Replace the thermostat or coolant temperature sensor if warm-up is the cause

Questions and answers

What does P016A mean?

The ECM decided the engine took too long to start controlling fuel using the oxygen sensor signal. The sensor or its circuit is the usual culprit.

Can I drive with code P016A?

Usually yes, but fuel economy and emissions can suffer. Get it checked soon to avoid possible catalytic converter damage.

Will replacing the oxygen sensor fix it?

Often, if the sensor is old and slow. Check wiring, the heater circuit, exhaust leaks and the thermostat first so you don't replace a good part.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.