Powertrain, generic (extended)

P2AFF Engine Coolant Temperature Sensor 4 Circuit High

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

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.

Likely causes

Open signal wire or unplugged connector

Chafed engine harness

Sensor element open internally

Symptoms

Check engine light after two trips
Implausibly cold coolant temperature in live data
Thermal management running on a default value

Repair estimate

DifficultyEasyDIY possible

Parts and labour€30–300

Time0.3–2 h

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

Parts involved

engine coolant temperature sensor 4wiring harnessecm

References: gsi.ext.gm.com, static.nhtsa.gov, ntn-snr.com.