P2257–P2259 AIR System Control A Circuit Low
The voltage on this circuit is sitting near zero. Typically a short to earth, or a sensor that has failed to its low end.
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 |
|---|---|---|
P2257 | AIR System Control A Circuit Low | Investigate soon |
P2259 | AIR System Control B Circuit Low | Investigate soon |
The definition
P2257: AIR System Control A Circuit Low.
P2257 is a manufacturer-specific powertrain code (the engine or gearbox). Its meaning is set by the carmaker rather than by the SAE standard, so a generic OBD-II reader will often show it as an unknown code or misread it.
What to check first
Cheapest and fastest checks first:
- Unplug the sensor. If the reading jumps to full scale, the wiring is fine and the sensor has failed low.
- Check the sensor's 5V supply and its earth before condemning the sensor itself.
What actually causes this on a VAG
'AIR system' here means secondary air injection, fitted to many VAG petrol engines. An electric pump blows fresh air into the exhaust ports for a short window after a genuinely cold start, so the catalysts light up quickly and cold-start emissions drop. VAG's own wording for this code is 'Secondary air injection System Control "A" Circuit low'. Control 'A' is one specific ECU output - on VAG applications that is the secondary air pump relay circuit. It is not a fault in the changeover valve, which has its own separate codes, and it is not by itself proof that the pump is dead. 'Low' means the ECU sees that output being pulled down: a short to earth on the control wire, or a shorted relay coil. It has no effect on how the car drives once warm, but the engine light will be on and that alone fails an MOT.
Most likely causes, in order
- Secondary air pump relay (coil side) or its socket. A shorted relay coil, or corrosion in the socket bridging the control pin to earth, gives exactly this. It is the cheapest thing to prove: swap in a known-good identical relay and re-read. It lives in the engine bay fuse box or a relay carrier depending on model. Worth knowing what this code is not - burnt contacts inside the relay stop the pump running and store an air-flow fault instead, not a control-circuit fault.
- Chafed control wire shorting to earth. A rubbed-through control wire touching earthed bodywork gives a permanent low reading. Check where the loom passes bulkhead grommets, bracket edges and anywhere previous work has disturbed or re-taped the harness.
- Corroded wiring or plug at the pump or relay carrier. Secondary air components are often mounted low at the front of the car or inside a wheel arch liner, exactly where road spray and winter salt reach the connectors. Pull the liner back, unplug and look for a green, wet or crumbling plug.
- ECU output stage fault. Possible but uncommon, and only a fair conclusion once the relay, its socket and the control wiring have all been proved good.
Worth knowing: The pump only runs for a short window after a genuinely cold start, so poking at it on a warm engine tells you nothing at all. Use the output test or basic settings function in a VAG-capable diagnostic tool to command the pump on demand - you should hear an unmistakable loud whoosh - rather than replacing parts on guesswork. And remember this is a control-circuit code: it says the ECU cannot drive its output cleanly, not that the pump has failed.
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 P2257 mean?
P2257 means AIR System Control A Circuit Low. The voltage on this circuit is sitting near zero. Typically a short to earth, or a sensor that has failed to its low end.
Can I drive with P2257?
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.