P2AA8Engine Coolant Bypass Valve B Position Sensor Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- With P2AA8 the position sensor of coolant valve B delivers an electrically valid signal, but its content is implausible: it sticks while the motor turns the valve, jumps by more than a real valve could move, or lies outside the end stops the module learned. A worn sensor track, a magnet that has shifted on the valve shaft or a slipping gear between motor and sensor are typical findings. No manufacturer documents P2AA8 publicly. GM's 2025 diesel tables for the comparable valve C do not use a separate sensor plausibility code; they judge position against target and set the valve code P26BB once the deviation exceeds 12 degrees for 8 of 10 seconds, Type B. For valve B that valve-level check is P26B0, while P2AA8 is aimed at the sensor itself. Pure circuit faults are P2AA7, P2AA9 and P2AAA.
- What you may notice
- Malfunction indicator lamp on
- Engine warms up slowly or runs hotter than usual
- Heater output varies
- Likely causes
- LikelyWorn or contaminated position sensor in the valve module
- PossibleSlipping gear or shifted magnet between valve shaft and sensor
- PossibleIntermittent contact in the connector causing signal jumps
- RareLearned end stops lost after a module or valve replacement
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.