Ageing, contaminated or slow oxygen sensor at Bank 1 Sensor 3; Exhaust leak near the sensor or upstream of it letting in false air; Damaged wiring, poor connector contact or corrosion in the sensor circuit; Sensor heater circuit fault, fuse or relay problem delaying sensor warm-up; Underlying fuelling or mixture fault such as a vacuum leak, injector fault or fuel pressure problem; Degraded catalyst affecting the gas reaching the sensor, depending on the exhaust layout; Outdated or faulty engine control unit calibration, where the manufacturer has issued a fix for this code.

P019A

O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 3.

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
9A: FaultThe specific fault in that area

What it means

P019A is the generic code for a delayed response from the oxygen sensor at Bank 1, Sensor 3 when the mixture swings from rich to lean. The engine control unit saw that sensor take too long to switch from a rich reading to a lean reading, compared with what it expects. Bank 1 is the side with cylinder 1, and the position of Sensor 3 depends on the exhaust layout, so check the model's wiring diagram.

Symptoms

Engine warning light on
Little or no change in driveability in many cases
Slightly poorer fuel economy
Possible rough running or hesitation if a fuelling fault is also present
Failed emissions test
Other fuel trim or oxygen sensor codes stored alongside it

Possible causes

Ageing, contaminated or slow oxygen sensor at Bank 1 Sensor 3likely
Exhaust leak near the sensor or upstream of it letting in false airlikely
Damaged wiring, poor connector contact or corrosion in the sensor circuitpossible
Sensor heater circuit fault, fuse or relay problem delaying sensor warm-uppossible
Underlying fuelling or mixture fault such as a vacuum leak, injector fault or fuel pressure problempossible
Degraded catalyst affecting the gas reaching the sensor, depending on the exhaust layoutrare
Outdated or faulty engine control unit calibration, where the manufacturer has issued a fix for this coderare

How to diagnose

Read all stored and pending codes and the freeze frame data to see engine load, temperature and fuel trims when the fault was set.
Check for related codes, especially other oxygen sensor, misfire, fuel trim or catalyst codes, and deal with those first.
Inspect the sensor wiring and connector for chafing, heat damage, water ingress, corrosion and loose pins.
Look and listen for exhaust leaks around the manifold, joints, flexible section and the sensor mounting.
Check the sensor heater circuit supply, earth, fuse and resistance against the manufacturer's specification.
Identify which sensor is Bank 1 Sensor 3 for this model and engine, then watch its live voltage or signal response during a steady warm-up and snap throttle test.
Check short and long term fuel trims for signs of a vacuum leak, fuel delivery fault or injector problem.
Check for an applicable calibration update or technical bulletin for this model.

How to fix

Repair any exhaust leaks and replace faulty gaskets or sections.
Repair or replace damaged wiring, terminals or connectors in the sensor circuit.
Replace the oxygen sensor if it is slow, contaminated or failing its heater check.
Rectify any underlying mixture fault, such as a vacuum leak or fuel delivery problem, found during testing.
Replace a failed fuse, relay or heater supply component if the heater circuit is at fault.
Apply a manufacturer calibration update only if one is published for this fault.

Can I keep driving?

Low severity

The car can usually be driven normally while you book it in for diagnosis. Do not leave it for long, as an underlying mixture fault could affect fuel economy, emissions and the catalyst.

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