P013E: O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 2
What to do
Ask for the exhaust to be checked for leaks ahead of the sensor. A leak lets air into the exhaust and makes the sensor respond late, and it is a common cause of this fault with a perfectly good sensor — often audible as a ticking or blowing noise, loudest when the engine is cold.
Mention any exhaust work the car has had, since a sensor not screwed fully home or fitted into the wrong port produces this directly.
Mention whether the engine burns oil. Oil ash builds up over the sensor's protective shield and slows it down physically.
The car will usually drive normally. This affects emissions monitoring rather than running, so plan the repair around your MOT rather than treating it as urgent.
What this code means
The downstream oxygen sensor on bank 1 is not beginning its rich-to-lean transition when it should.
Delayed response measures dead time — the gap between the mixture actually changing and the sensor noticing. That is a different fault from a sensor that responds slowly once it starts, and it points somewhere different.
Dead time usually means the gas is not reaching the sensor promptly, or is not the gas the module thinks it is.
- An exhaust leak upstream lets fresh air in and dilutes the sample, so the transition arrives blurred and late.
- A sensor not seated to depth, or sitting in a pocket rather than the flowing stream, sees the gas after the main flow has passed.
- A build-up of soot or oil ash over the sensor's protective shield physically slows gas exchange around the element while leaving its electrical behaviour intact.
The direction is diagnostic too, and this is the rich-to-lean case. Contamination on the element tends to hold a sensor rich, because the residue continues to consume oxygen at the surface after the exhaust has gone lean. A delay that is markedly worse in this direction than the other points at a fouled element rather than at a leak, which would delay both roughly equally.
So compare the two directions before deciding. A sensor delayed in one direction only is telling you something a sensor delayed in both is not.
Likely causes
Start here
- Exhaust leak upstream of the sensor · moderate
- Oxygen sensor not correctly seated · moderate
- Aging or slow oxygen sensor · moderate
Less common
- Metal debris on the sensor tip · moderate
- Engine burning oil into the exhaust · specialist
Symptoms
Components involved
Information, not instruction
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