What it means
The control circuit of the secondary air injection system A reads a voltage below specification. Either the relay output is shorted to ground or the wiring/load is faulty.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Secondary air injection pumps fresh air into the exhaust during cold starts to help the catalytic converter warm up. P2257 sets when the module detects that control circuit A is below its expected voltage, which can prevent or disrupt the commanded air injection.
Common causes
Most likely first.
- Control wire shorted to ground
- Faulty SAI relay
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light on
- Rough running or increased emissions during cold starts
- Failed emissions inspection
How to diagnose it
- Read freeze-frame data and check whether P2257 occurs during a cold start when the secondary-air system is commanded on.
- Inspect the control A wiring, relay connector, and related terminals for corrosion, chafing, loose pins, or heat damage.
- Check the control wire for a short to ground, following the vehicle wiring diagram and service information.
- Test the secondary-air relay and its output under the commanded operating condition to see whether it switches correctly.
- If the wiring and relay are sound, check the circuit load and module control against the manufacturer's specification.
Common fixes
- Clean or repair corroded control A connector terminals.
- Repair a control wire shorted to ground or damaged harness section.
- Replace a faulty secondary-air relay.
- Repair the failed circuit load or connection identified by testing.
Can I keep driving?
Ordinary driving is usually possible, but cold-start emissions may rise and the vehicle may fail an emissions inspection. Avoid repeated cold-start trips until the fault is repaired if rough running occurs.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.