P2AFC: Engine Coolant Temperature Sensor 4 Circuit

P2AFC is the general circuit code for a fourth engine coolant temperature sensor. Engines with split cooling, electric pumps or separate head, block, radiator and heater circuits carry several such sensors, and how they are numbered is up to each maker. No manufacturer documents a set condition for P2AFC publicly; for the 2019 L3B 2.7-litre engine GM instead assigns separate low and high codes to this sensor (P2AFE, P2AFF). Supplier NTN-SNR describes P2AFC in its coolant sensor catalogue as an electrical defect in the circuit of sensor 4. CARB requires coolant temperature inputs to be monitored for broken circuits and for values outside their range. Expect an open line, a loose plug or a failed NTC element; the engine computer then falls back on a substitute value.

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 on
Cooling fans running more than usual on substitute value
Thermal management in default mode

Most likely causes

Open wire or loose connector at sensor 4
Failed NTC element in sensor 4
Faulty input stage 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
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 P2AFC means

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

Frequently asked questions

Can I keep driving with code P2AFC?

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 P2AFC?

The most common causes are: open wire or loose connector at sensor 4; failed NTC element in sensor 4; faulty input stage 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.