Faulty engine coolant temperature sensor (internal failure or degraded thermistor); Corroded, loose, or damaged electrical connector at the ECT sensor; Chafed or broken wires in the ECT sensor circuit (signal or ground); Coolant level low or air pockets causing the sensor to read erratically; Contaminated or degraded coolant affecting sensor response; ECM internal fault or poor ground connection at the ECM; Aftermarket sensor with incorrect resistance curve installed

DTC codes / GM codes / P1116

P1116 · GMEngine Coolant Temperature Sensor Erratic

Q: What does code P1116 mean?

Engine Coolant Temperature Sensor Erratic. P1116 on a GM vehicle means the engine control module (ECM) has detected an erratic signal from the engine coolant temperature (ECT) sensor circuit. The ECM expects the sensor voltage to change smoothly as the engine warms up, but instead it sees sudden jumps, dropouts, or implausible readings that do not match other temperature inputs.

P1116 on a GM vehicle means the engine control module (ECM) has detected an erratic signal from the engine coolant temperature (ECT) sensor circuit. The ECM expects the sensor voltage to change smoothly as the engine warms up, but instead it sees sudden jumps, dropouts, or implausible readings that do not match other temperature inputs.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Check engine light illuminated, often with no other noticeable symptoms
Erratic or inaccurate temperature gauge reading on the dashboard
Poor fuel economy or rich-running condition because the ECM misjudges coolant temperature
Hard starting or rough idle when the engine is cold or hot
Cooling fan running constantly or not engaging when needed
Intermittent stalling or hesitation during warm-up

Common causes, most likely first

Faulty engine coolant temperature sensor (internal failure or degraded thermistor)
Corroded, loose, or damaged electrical connector at the ECT sensor
Chafed or broken wires in the ECT sensor circuit (signal or ground)
Coolant level low or air pockets causing the sensor to read erratically
Contaminated or degraded coolant affecting sensor response
ECM internal fault or poor ground connection at the ECM
Aftermarket sensor with incorrect resistance curve installed

How to diagnose and fix it

Scan all modules and record freeze-frame data for P1116 to see when the erratic signal occurs
Inspect the ECT sensor connector and wiring for corrosion, looseness, or damage; repair as needed
Check coolant level and condition; top off or flush if contaminated or low
Measure ECT sensor resistance with a multimeter and compare to GM specifications for the current temperature
Backprobe the sensor signal wire at the ECM and watch for voltage jumps while wiggling the harness
Replace the ECT sensor with a genuine GM or OEM-equivalent part if resistance testing is out of spec
Clear codes and perform a road test to verify the erratic signal is gone and no pending codes return

Why an erratic ECT signal fools the ECM

A sensor that tests fine at room temperature can still be erratic when hot, so always test resistance both cold and after warming the engine.
Corroded terminals inside the ECT connector often cause this code without any visible damage on the outside, so unplug and inspect the pins closely.
Low coolant or trapped air can make the sensor read erratically because the tip is not continuously immersed in coolant.
The ECM compares ECT with intake air temperature and engine run time; a slow-to-rise sensor can set P1116 even if it never goes open circuit.
Aftermarket sensors with the wrong resistance curve are a common cause of repeat P1116 codes after a repair.

Can I keep driving with P1116?

You can usually drive with P1116, but avoid long trips or heavy load until it is diagnosed because erratic coolant temperature data can affect fuel mixture and cooling fan operation. If the temperature gauge swings wildly or the engine overheats, stop driving and have it checked immediately.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.