P0136: the rear oxygen sensor circuit has a fault
A second oxygen sensor sits in the exhaust after the catalytic converter and checks how well the converter is cleaning up the exhaust, rather than fine-tuning the fuel mixture the way the front sensor does. This code means the electrical circuit for bank 1's rear sensor isn't behaving the way the engine control unit expects. It covers the wiring, connector and sensor together, without saying which one is at fault.
You might notice
- The engine warning light comes on
- No other symptom you'd notice while driving, since this sensor doesn't control fuelling
- oxygen sensor
- — a sensor in the exhaust that measures how much oxygen is left after combustion
- catalytic converter
- — the part of the exhaust that cleans up the gases before they leave the car
What the code itself says
P0136 is a powertrain (engine, gearbox and drive system) code, and the 0 after the letter means it is a generic code with a standard meaning.
Grouped here as: Engine running, fuelling and misfires — Air metering, fuelling, ignition, misfire, idle, boost, knock, oxygen sensors and the catalyst, all working together in the running engine. That grouping is ours, to help explain the code. The code's official family is the letter at the start.
This page is generic. Your car isn't.
A code on its own only tells you what the sensor saw, not what's actually wrong — and that changes next to your other codes. Read this one together with the rest of your scan and we'll work out what's really going on.
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