OBD-II code · Powertrain (generic, extended)
P20A8 Reductant Injection Air Pressure Control Valve Circuit Low
Reductant air-pressure control valve drive line stuck low — short to ground. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P20A8?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyShort to ground
- Less likelyConnector pins corroded - high contact resistance
- Less likelyHarness chafing through insulation
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.7–2.5 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Air Pressure Control Valve
Related codes
- P20A6Reductant Injection Air Pressure Control Valve Circuit/Open
- P20A5Reductant Purge Control Valve A Stuck Closed
- P20A7Reductant Injection Air Pressure Control Valve Performance
- P20A9Reductant Injection Air Pressure Control Valve Circuit High
- P20AAReductant Injection Air Pressure Control Valve Stuck Open
- P20ABReductant Injection Air Pressure Control Valve Stuck Closed
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.