P2059
Reductant Injection Air Pump Control Circuit/Open
Diesel exhaust aftertreatment (SCR)
Generic OBD-II
Medium
What it means
P2059 means the aftertreatment controller detected an open in the control circuit for the reductant (DEF) injection air pump. On air-assisted diesel SCR systems this pump helps atomize the reductant for NOx control. An open circuit usually points to broken wiring, a failed pump, or a fuse/relay fault, and can lead to a power derate as the system protects emissions compliance.
Medium
Can I keep driving? Usually driveable at first, but many diesels reduce power (derate) when SCR dosing can't run — repair it before the vehicle limits performance.
Common symptoms
What you'll notice
- Check-engine light on
- SCR / DEF or emissions-system warning message
- Possible reduced power (engine derate)
- Increased NOx / failed emissions readiness
Common causes
Most likely first
- Open circuit or break in the reductant air pump control wiringLikely
- Failed reductant injection air pumpCommon
- Corroded or loose connector at the pumpCommon
- Blown fuse or failed control relay for the pumpLess often
- Faulty PCM/aftertreatment control module — less commonLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and inspect the air pump connector and control wiring for an open circuit.
- Check the pump's power feed, ground, fuse, and control relay.
- Test the reductant air pump's resistance and operation; replace it if it does not run.
- If wiring and pump are good, have the control module evaluated. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2059?+
Short-term usually, but the SCR system may derate power when the air pump can't assist dosing. Repair it before the vehicle limits performance.
Can I just clear P2059?+
The open-circuit fault returns until the wiring or pump is repaired, and clearing won't stop an emissions-related derate.
Related codes
Often seen with P2059
Read & clear P2059 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