OBD-II code · Powertrain (generic, extended)
P2AA9 Engine Coolant Bypass Valve B Position Sensor Circuit Low
Voltage on the engine coolant bypass valve B position sensor signal line is below the expected window. Wire shorted to ground or sensor short.
Is it safe to drive with P2AA9?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySignal wire shorted to ground
- PossibleInternal sensor short
- Less likelyConnector pins corroded - high contact resistance
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–3 h
- Emissions test
- Usually unaffected
- Parts involved
- Engine Coolant Bypass Valve B Position Sensor, Wiring Harness, Ecm
Related codes
- P23C4Engine Coolant Bypass Valve C Position Sensor Circuit Low
- P26A6Engine Coolant Bypass Valve A Position Sensor Circuit Low
- P2AA6EGR Cooler Bypass Control Circuit Driver Current/Temperature Too High Bank 2
- P2AA7Engine Coolant Bypass Valve B Position Sensor Circuit
- P2AA8Engine Coolant Bypass Valve B Position Sensor Range/Performance
- P2AAAEngine Coolant Bypass Valve B Position Sensor Circuit High
- P2AABEngine Coolant Bypass Valve B Position Sensor Circuit Intermittent/Erratic
- P2AACDiesel Fuel Presence Sensor Circuit
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.