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P2257 – Secondary Air Injection System Control A Circuit Low (OBD2)

P2257 means "Secondary Air Injection System Control A Circuit Low". The voltage the control unit measures in the secondary air injection system circuit is below the permitted minimum. For a sensor this usually means the signal wire is shorted to ground or the reference voltage is missing; for an actuator, that its control wire is shorted to ground.

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P2257 quick summary

Fault codeP2257
MeaningSecondary Air Injection System Control A Circuit Low
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityLow
Can I drive?Yes. The engine runs normally, but cold-start emissions are higher and the car may fail the emissions test.
Repair cost€20 – €700

How the secondary air injection system works

The secondary air system pumps fresh air into the exhaust for the first minute or two after a cold start, so the catalytic converter heats up faster and cold-start emissions fall.

An electric air pump blows air through a combination (check) valve into the exhaust ports. The extra oxygen burns the rich cold-start exhaust in the manifold, heating the catalytic converter. The check valve prevents exhaust from flowing back into the pump; it is opened by vacuum through a solenoid or by air pressure.

The control unit monitors the system with the oxygen sensors or a pressure sensor: when the pump runs, the oxygen sensor should show a lean signal. If not, it stores flow codes (P0410, P0411, P0491, P0492); other codes cover the switching valves and the pump relay.

The pump often fails because moisture or exhaust gas gets into it through a leaking check valve. Carbon can also block the air passages in the cylinder head. Faults do not affect driving, but the car will not pass an emissions inspection with the Check Engine light on.

Symptoms of P2257

  • Check Engine light on
  • No pump noise after a cold start – or a loud whine/rattle from the pump
  • Usually no driving symptoms
  • Failed emissions test

Most common causes of P2257 (most likely first)

Mechanic's Pro Tip

If the pump is full of water or soot, replace the check valve along with it – a leaking check valve is usually why the pump died, and the new pump would suffer the same fate.

  1. 1.Signal or control wire shorted to ground

    Most likely

    Look for chafed insulation where the harness touches the engine, exhaust brackets or body edges.

  2. 2.Missing 5 V reference or supply voltage

    An open reference wire or a shorted sensor elsewhere on the same reference circuit can pull it down.

  3. 3.Internal short in the secondary air injection system

  4. 4.Failed secondary air pump

    Moisture or exhaust gas damages the motor.

  5. 5.Sticking or leaking check (combination) valve

  6. 6.Faulty pump relay, fuse or switching valve

  7. 7.Cracked air or vacuum hoses

Step-by-step diagnostic guide

  1. 1

    Read codes

    Read all codes and note whether they concern flow, the switching valves or the relay.

  2. 2

    Measure the signal voltage

    With the ignition on and the secondary air injection system plugged in, back-probe the signal wire. Then unplug it and check the reference/supply and ground wires separately.

    Multimeter: Signal near 0 V = short to ground or no reference. Reference wire: about 5 V with ignition on. Signal wire to ground with connector unplugged: no continuity.

  3. 3

    Listen at cold start

    Listen for the pump during the first minute after a cold start. No noise points to the pump, relay or fuse.

  4. 4

    Check relay, fuse and power

    Check the relay and fuse, and measure the supply voltage at the pump when it should run.

  5. 5

    Check valve and hoses

    Check the check valve for exhaust deposits and correct operation, and the hoses for cracks.

    Multimeter: Vacuum-operated valves should open with about 0.3–0.5 bar vacuum and seal when released.

  6. 6

    Run the system test

    Use the scan tool to run the secondary air test and watch the oxygen sensor go lean when the pump runs.

Frequently asked questions

Can I keep driving with P2257?

Yes. The engine runs normally, but cold-start emissions are higher and the car may fail the emissions test.

How much does it cost to fix P2257?

Typical repair costs are 20 € – 700 €, depending on the cause and the vehicle. The most common fixes are: signal or control wire shorted to ground; missing 5 V reference or supply voltage; internal short in the secondary air injection system. Always confirm the cause with the tests above before buying parts.

Is the secondary air system necessary?

Yes, for emissions approval. Disabling it is illegal and the Check Engine light will stay on.

Why does the pump only run for a minute?

It is only needed while the catalytic converter warms up after a cold start.

What is the difference between P2257 and similar codes?

P2257 belongs to a group of codes for the same component that differ in the type or location of the fault: P0419 – Secondary Air Injection System Relay B Circuit Malfunction; P0491 – Secondary Air Injection System (Bank 1); P0492 – Secondary Air Injection System (Bank 2); P2258 – Secondary Air Injection System Control A Circuit High; P2440 – Secondary Air Injection System Switching Valve Stuck Open Bank 1; P2441 – Secondary Air Injection System Switching Valve Stuck Closed Bank 1. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.