P046A–P046B Catalyst Temperature Sensor 1/2 Correlation Bank 1
Two sensors that should agree with each other do not, so the ECU cannot tell which one to trust.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P046A | Catalyst Temperature Sensor 1/2 Correlation Bank 1 | Investigate soon |
P046B | Catalyst Temperature Sensor 1/2 Correlation Bank 2 | Investigate soon |
The definition
P046A: Catalyst Temperature Sensor 1/2 Correlation Bank 1.
P046A is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
- Check the connector at the part for corrosion, and that it is fully seated.
- Clear the code and see whether it returns, and under what conditions.
What actually causes this on a VAG
Exhaust temperature sensors sit in the exhaust and tell the ECU how hot the gas is at various points, so it can protect the turbo and catalyst and, on a diesel, decide when the particulate filter can be regenerated. A "correlation" fault means two of these sensors on the same bank are disagreeing in a way the ECU cannot explain - not that either is necessarily dead, but that their readings do not add up together. Note what that implies: the code deliberately does not tell you which of the two is wrong, only that they no longer agree, which is why the cold-soak test below is the step that actually moves you forward. Bank 1 is the side of the engine containing cylinder 1; on a four-cylinder there is only one bank. This is not a diesel-only code - turbo petrol engines carry exhaust temperature sensors for turbo and catalyst protection too, and there the usual consequence is enrichment or a power restriction rather than a regeneration problem.
Most likely causes, in order
- Damaged sensor wiring or a loose connector. Free to check and where you should start. The leads run along the hot exhaust and are exposed to road salt and spray. Melted or chafed insulation, a green connector, or a plug that has vibrated loose all produce implausible readings from a perfectly good sensor. Inspect the full run of each lead, not just the plug ends, before ordering anything.
- One exhaust temperature sensor drifting out of range. This is the usual answer. These sensors live in extreme heat and are heat-cycled thousands of times, and they commonly drift rather than fail outright. The confirming check is free and it is the one that names the culprit: with the car stone cold after standing overnight, every exhaust temperature reading in live data should be close to the outside air temperature. Whichever one disagrees at cold soak is your suspect - and now you are replacing a specific sensor rather than a pair.
- An exhaust leak between the two sensors. A blowing joint, cracked manifold or leaking clamp lets cool air in and genuinely changes the temperature at one sensor, so both sensors can be perfect and still disagree. Listen for a blow at cold start, when it is loudest, and look for sooty streaks around joints and clamps.
- Poor earth or a wider sensor supply fault. Where several sensors share a supply or ground, one bad connection can throw the comparison out. Worth checking if more than one temperature reading looks odd at the same time, or if other apparently unrelated sensors are complaining alongside.
Worth knowing: On a diesel with a particulate filter, do not leave this. The ECU relies on these temperatures to decide it is safe to regenerate, and a sensor it does not trust can stop regenerations happening at all - so the filter quietly loads with soot while you drive around with only a warning light to show for it. A cheap sensor now is a great deal better than a blocked filter later. One practical warning before you book the job: these sensors seize into the exhaust and frequently snap off on removal, which turns a modest part into a manifold or exhaust section repair. Soak the threads, get the exhaust warm before you try, and go in expecting that possibility rather than being surprised by it.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P046A mean?
P046A means Catalyst Temperature Sensor 1/2 Correlation Bank 1. Two sensors that should agree with each other do not, so the ECU cannot tell which one to trust.
Can I drive with P046A?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.