P2AAA: Engine Coolant Bypass Valve B Position Sensor Circuit High

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.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. With the engine cold, check the coolant level; never do this when the system is hot
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Check the actual temperature in live data
4. Make sure the fan comes on when it should
5. Check the thermostat and connector
6. Measure the sensor and replace it if its readings do not make sense

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P2AAA means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• A: Hybrid or air and fuel
• AA: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2AAA?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P2AAA?

The most common causes are: 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.

Related codes

• P2AA9Engine Coolant Bypass Valve B Position Sensor Circuit Low
• P2AA7Engine Coolant Bypass Valve B Position Sensor Circuit
• P2AA8Engine Coolant Bypass Valve B Position Sensor Circuit Range/Performance
• P2AABEngine Coolant Bypass Valve B Position Sensor Circuit Intermittent/Erratic
• P26A7Engine Coolant Bypass Valve A Position Sensor Circuit High
• P23C5Engine Coolant Bypass Valve C Position Sensor Circuit High

Sources

• gsi.ext.gm.com: 25OBDG04B
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.