OBD-II code · Powertrain (generic, extended)
P2039 Reductant Injection Air Pressure Sensor A Circuit Low
The reductant injection air-pressure sensor A reads below its lower plausibility limit — short to ground or sensor internal short.
Is it safe to drive with P2039?
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 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Air Pressure Sensor
Related codes
- P2037Reductant Injection Air Pressure Sensor A Circuit
- P209CReductant Injection Air Pressure Sensor B Circuit Low
- P2036Exhaust Gas Temperature Sensor Circuit High (Bank 2 Sensor 2)
- P2038Reductant Injection Air Pressure Sensor A Circuit Range/Performance
- P203AReductant Level Sensor A Circuit
- P203BReductant Level Sensor A Circuit Range/Performance
- P203CReductant Level Sensor A Circuit Low
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.