P2259
AIR System Control B Circuit Low
Secondary air injection
Generic OBD-II
Medium
What it means
P2259 sets when the PCM sees low voltage on the "B" control circuit for the secondary air injection (SAI) system — the pump that forces fresh air into the exhaust at cold start to help the catalytic converter light off quickly. It usually points to a short to ground or an open in the control wiring. The engine typically runs normally; the main consequence is failing emissions.
Medium
Can I keep driving? Yes — the car drives normally; this is an emissions-system circuit fault that mainly affects cold-start emissions and will fail an emissions test until fixed.
Common symptoms
What you'll notice
- Check-engine light on — often the only symptom
- May fail an emissions or smog test
- Possible slightly rough running right after a cold start
Common causes
Most likely first
- Short to ground or open in the SAI control 'B' circuit wiring or connectorLikely
- Faulty secondary air injection pump relay or control solenoidCommon
- Corroded or damaged connector at the SAI pump/solenoidCommon
- Air pump or check valve fouled with carbon or moistureLess often
- Faulty PCM (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame and inspect the SAI control 'B' circuit wiring and connectors for damage, corrosion, or a short to ground.
- Check the SAI pump relay and control solenoid; verify their power and ground.
- Measure the control-circuit voltage/resistance against the manufacturer's spec.
- Inspect the air pump and check valve for carbon or water intrusion.
- Repair the wiring or component, clear the code, and confirm the SAI monitor runs.
FAQ
Quick answers
Is it safe to drive with P2259?+
Yes. It's an emissions circuit fault with no real effect on power or safety, but repair it so the car passes emissions and the catalyst warms correctly at startup.
Can I just clear P2259?+
You can, but it returns once the SAI system is commanded again (typically the next cold start) unless the circuit fault is fixed.
Related codes
Often seen with P2259
Read & clear P2259 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX