Powertrain, generic (extended)

P2AAA Engine Coolant Bypass Valve B Position Sensor Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

With P2AAA the position sensor of coolant valve B reports a value above anything a working sensor would deliver. Typical reasons are a signal line touching a supply wire, a damaged output stage inside the sensor or, depending on how the input is wired, an interrupted ground. Since the engine computer can no longer tell where the valve really stands, it loses closed-loop control and has to rely on a fixed default position. No manufacturer documents P2AAA publicly. GM's code for the comparable valve C, P23C5, flags a SENT value above 4,050 counts, again over 4 of 5 seconds and as Type B, and names a short to power as the cause. CARB requires input components to be checked for wiring faults and for readings beyond their limits. P2AA9 is the low counterpart, P2AAB the sporadic one.

Likely causes

Signal wire in contact with a supply or reference voltage wire
Sensor ground open at the connector or splice
Position sensor in the valve module defective

Symptoms

  • Check engine light on
  • Coolant temperature swings or stays off target
  • Possibly reduced engine power if the module protects against overheating

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

engine coolant bypass valve b position sensorwiring harnessecm

Related codes

P2AA9P2AA7P2AA8P2AABP26A7P23C5

References: gsi.ext.gm.com, law.cornell.edu.