P013F: O2 Sensor Delayed Response - Lean to Rich Bank 1 Sensor 2
What to do
Ask for both directions of the sensor's response to be compared, if that has not been done. A sensor that is late in both directions usually means an exhaust leak; late in only one direction points at the sensor itself. That distinction decides whether a part is needed at all.
Ask for the sensor body to be inspected for cracks or corrosion damage. These sensors draw a reference from the outside air through their body, and a crack lets air into the measurement — which produces this fault specifically.
Mention any exhaust work, and any knocks to the underside of the car.
The car will drive normally. This is an emissions monitoring fault, so time the repair around your MOT.
What this code means
The downstream oxygen sensor on bank 1 is not beginning its lean-to-rich transition when it should.
This is the opposite direction from its sibling, and reading the pair together is more informative than reading either alone.
A delay that appears in both directions is a transport problem — the gas is reaching the sensor late. An exhaust leak, a sensor sitting out of the main flow, or a badly positioned port all delay everything equally, because they affect when the sample arrives rather than how the element behaves.
A delay in the lean-to-rich direction specifically has a narrower explanation. Going rich means oxygen disappearing from the exhaust, and the sensor reports that by the oxygen at its element falling. Anything that holds oxygen at the element delays exactly this transition and not the other — most commonly a leak drawing fresh air in close to the sensor, or a cracked sensor body letting its own reference air into the measurement side.
A cracked or damaged sensor body is worth looking for physically here. These sensors take their reference from ambient air through the body, and a crack — from impact, corrosion or over-tightening — feeds atmosphere directly onto the measuring element.
On a downstream sensor the practical consequence is emissions monitoring rather than driveability, since this sensor judges the catalytic converter rather than trimming the fuelling.
Likely causes
Start here
- Exhaust leak upstream of the sensor · moderate
- Aging or slow oxygen sensor · moderate
Less common
- Cracked or damaged oxygen sensor body · moderate
- Oxygen sensor not correctly seated · moderate
- Metal debris on the sensor tip · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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