P2AFE: Engine Coolant Temperature Sensor 4 Circuit Low

Coolant sensors are NTC thermistors, so a signal from sensor 4 that is too low stands for an impossibly hot reading, usually a signal wire grounded or a shorted element. GM documents P2AFE for the 2.7 L turbo four (L3B) in its 2019 tables: the configurable temperature input system sets it when the resistance of the sensor 4 channel drops below about 41 Ω, corresponding to 150 °C, for 5 s within a 6 s window; Type B, so the MIL follows on the second trip. In bulletin 21-NA-149 GM names P2AFE as one consequence of engine harness chafing on 2019 to 2021 Silverado and Sierra 1500 trucks, the 2.7 L included. Because a hot reading is first taken at face value, the fans may run at full speed. P2AFF is the opposite fault, P2AFD the plausibility check.

Medium severity. Can I keep driving?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.

Symptoms

Check engine light after two trips
Cooling fans running at full speed
Implausibly high coolant temperature in live data

Most likely causes

Signal wire shorted to ground, for example by harness chafing
Internally shorted sensor
Faulty input in the engine control module

What to check, in order

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

With the engine cold, check the coolant level; never do this when the system is hot
With the connector unplugged, check whether the signal wire is making contact with ground.
Check the actual temperature in live data
Make sure the fan comes on when it should
Check the thermostat and connector
Measure the sensor and replace it if its readings do not make sense

Good to know

Repair difficulty: easy
It affects emissions.

What each character of P2AFE means

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

Frequently asked questions

Can I keep driving with code P2AFE?

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 P2AFE?

The most common causes are: signal wire shorted to ground, for example by harness chafing; internally shorted sensor; faulty input in the engine control module.

Related codes

Sources

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.