Faulty oxygen or air/fuel ratio sensor heater circuit or slow sensor, so it is slow to reach operating temperature; Wiring, connector or fuse/relay fault in the sensor heater supply or signal circuit; Engine coolant temperature sensor reading incorrectly, or a thermostat stuck open so the engine warms up too slowly; Exhaust leak upstream of the sensor letting in air and giving false readings; Contaminated or aged sensor from oil, coolant or fuel additives; Outdated or faulty ECU software calibration, where the manufacturer has issued an update for the model.

P016A

Excessive Time To Enter Closed Loop Air/Fuel Ratio Control.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
6A: FaultThe specific fault in that area

What it means

P016A is a generic powertrain code meaning the engine control unit took longer than expected to enter closed loop air/fuel ratio control after start-up. In closed loop the ECU trims fuelling using oxygen or air/fuel sensor feedback, which needs the sensors to reach operating temperature and give valid readings. The code sets when that has not happened within the calibrated time, so the ECU has stayed on pre-set open loop fuelling for too long.

Symptoms

Malfunction indicator lamp on
Higher than normal fuel consumption, especially on short trips
Rough or unstable idle during warm-up
Poor cold running or hesitation
Possible failed emissions test
Possible additional oxygen sensor heater or coolant temperature codes

Possible causes

Faulty oxygen or air/fuel ratio sensor heater circuit or slow sensor, so it is slow to reach operating temperaturelikely
Wiring, connector or fuse/relay fault in the sensor heater supply or signal circuitlikely
Engine coolant temperature sensor reading incorrectly, or a thermostat stuck open so the engine warms up too slowlylikely
Exhaust leak upstream of the sensor letting in air and giving false readingspossible
Contaminated or aged sensor from oil, coolant or fuel additivespossible
Outdated or faulty ECU software calibration, where the manufacturer has issued an update for the modelrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting coolant temperature, engine load and time since start
Check for related codes such as oxygen sensor heater, sensor circuit, coolant temperature or thermostat codes, and deal with those first
Inspect the sensor wiring, connectors and relevant fuses for damage, corrosion, heat damage or water ingress
Using live data on a cold start, compare coolant temperature with a known ambient or true engine temperature and check it rises steadily to normal operating temperature
Watch the upstream sensor live data from cold and note how long it takes to become active and switch or respond; compare with the specification for that engine
Measure the heater circuit supply voltage, ground and heater resistance against the manufacturer's figures for that model
Inspect the exhaust manifold, joints and flexible sections upstream of the sensor for leaks
Check the engine is reaching normal temperature, and check with the manufacturer whether a software update applies to the vehicle

How to fix

Replace the faulty oxygen or air/fuel ratio sensor if the heater or response is out of specification
Repair damaged wiring, connectors, fuses or relays in the sensor heater circuit
Replace a faulty coolant temperature sensor or a thermostat that is stuck open
Repair exhaust leaks upstream of the sensor
Fix the source of any contamination (oil, coolant or fuel) before fitting a new sensor
Apply a manufacturer ECU software update only if one is published for this known issue

Can I keep driving?

Low severity

The car can normally be driven while you arrange a repair, as this code mainly affects fuelling during warm-up. Fix it soon to avoid higher fuel use and emissions, and have it checked sooner if the engine runs badly.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.