P2233: O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 1 Sensor 3
What to do
The car will drive normally; this sensor monitors the rear catalyst rather than controlling fuelling. If a converter has been diagnosed alongside it, ask for the wiring to be repaired and the fault cleared before anything expensive is agreed — this harness runs along the underside of the vehicle and is the most exposed of the three.
What this code means
The same short again, on a third sensor in the bank 1 exhaust stream. A third position implies more than one catalyst in series — a close-coupled converter near the manifold and a main one further back — so this sensor generally sits after the second of them.
Its function is the catalyst monitoring described at P2232, applied to the rear converter, and the same caution applies with extra force: on a vehicle with two converters, a monitoring fault at this position can be attributed to whichever catalyst is convenient. Establishing that the signal circuit is at fault is what prevents an expensive part being replaced on the strength of a reading that was never valid.
Being furthest from the engine, this sensor's harness is the most exposed of the three to road spray, salt and stone damage, which is where most of these faults originate.
Likely causes
Start here
- Damaged wiring harness · moderate
- Internal short in the oxygen sensor · moderate
- Water ingress into connector · easy
Less common
- Incorrectly wired universal oxygen sensor · moderate
- Melted wiring against the exhaust · 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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