What it means
The drive line for secondary air injection (AIR) control circuit B is stuck low. Secondary air is pumped into the exhaust manifold during cold start to speed up catalyst light-off.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Secondary air injection sends air into the exhaust during cold starts to speed catalyst warm-up. P2259 identifies a low voltage on control circuit B, meaning the module sees that circuit held below its expected level when it monitors or commands it.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check-engine light may illuminate
- Secondary-air system warning or emissions fault may be stored
- Usually no noticeable change in driving
How to diagnose it
- Check freeze-frame data and confirm whether the fault was recorded during a cold-start secondary-air command.
- Inspect control B wiring and its connectors for chafing, damaged insulation, corrosion, or loose pins.
- Trace the control B wire using the wiring diagram and check for a short to ground.
- Test connector contact and circuit continuity, accounting for any high resistance from corrosion.
- If the wiring checks pass, test the relay and module-controlled circuit against the manufacturer's specification.
Common fixes
- Clean or repair corroded control B connector pins.
- Repair harness chafing or a control B wire shorted to ground.
- Repair a loose or high-resistance connection in the circuit.
- Replace a failed relay or other circuit component if testing confirms it.
Can I keep driving?
Normal driving is usually unaffected, but cold-start emissions can increase and an emissions inspection may fail. Repair it promptly if a warning appears or cold starts become rough.
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.