P2AFF: Engine Coolant Temperature Sensor 4 Circuit High

P2AFF reports an excessive sensor 4 signal. For an NTC thermistor that means an implausibly cold reading, mostly from an open circuit, an unplugged connector or a line shorted to voltage. GM's 2019 tables for the 2.7 L L3B set P2AFF once the resistance rises above roughly 355 kΩ, equal to −60 °C, for 5 s in a 6 s window, with an engine run time above 10 s among the enabling conditions; Type B with MIL after two trips. Oddly, the same GM table names the radiator coolant sensor in the P2AFF row while assigning P2AFE to coolant sensor 4, but both channels share the same threshold. GM bulletin 21-NA-149 also lists P2AFF for chafed engine harnesses on its 1500 pickups. The engine computer then works with a substitute value. P2AFE is the short-to-ground case.

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
Implausibly cold coolant temperature in live data
Thermal management running on a default value

Most likely causes

Open signal wire or unplugged connector
Chafed engine harness
Sensor element open internally

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
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
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 P2AFF means

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

Frequently asked questions

Can I keep driving with code P2AFF?

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 P2AFF?

The most common causes are: open signal wire or unplugged connector; chafed engine harness; sensor element open internally.

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.