Faulty engine coolant temperature sensor; Damaged or corroded sensor wiring harness or connector; Open or shorted circuit in the sensor signal or ground wire; Coolant level low or air pockets causing inaccurate sensor readings; Failed thermostat stuck open or closed, affecting warm-up rate; Faulty engine control module, though rare

DTC codes / GM codes / P1185

P1185 · GMEngine Temperature Sensor Circuit

Q: What does code P1185 mean?

Engine Temperature Sensor Circuit. P1185 on a GM vehicle indicates that the engine control module has detected an abnormal signal from the engine coolant temperature sensor circuit, which is critical for fuel delivery and cooling fan operation. The computer compares the sensor voltage against expected values for the current operating conditions and flags the code when the reading falls outside the valid range or fails a rationality check.

P1185 on a GM vehicle indicates that the engine control module has detected an abnormal signal from the engine coolant temperature sensor circuit, which is critical for fuel delivery and cooling fan operation. The computer compares the sensor voltage against expected values for the current operating conditions and flags the code when the reading falls outside the valid range or fails a rationality check.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Poor fuel economy or rich-running condition due to incorrect temperature data
Erratic or high idle speed, especially after a cold start
Cooling fans running constantly or not engaging at all
Hard starting or stalling when the engine is cold
Temperature gauge on the dashboard reading incorrectly or not moving

Common causes, most likely first

Faulty engine coolant temperature sensor
Damaged or corroded sensor wiring harness or connector
Open or shorted circuit in the sensor signal or ground wire
Coolant level low or air pockets causing inaccurate sensor readings
Failed thermostat stuck open or closed, affecting warm-up rate
Faulty engine control module, though rare

How to diagnose and fix it

Verify coolant level and condition, then check for air pockets in the cooling system
Inspect the engine coolant temperature sensor connector and wiring for corrosion, chafing, or loose pins
Measure sensor resistance with a multimeter and compare to GM specifications for the ambient temperature
Backprobe the sensor signal wire at the engine control module and compare voltage to the sensor reading
Test the sensor circuit for opens and shorts using a wiring diagram and continuity tester
Replace the engine coolant temperature sensor if resistance is out of range or the signal is erratic
Clear the code and perform a road test to confirm the repair and ensure the monitor runs to completion

Coolant Sensor Circuit Checks That Save Time

A low coolant level or trapped air can cause the sensor to read cold even when the engine is warm, setting P1185 without any sensor fault at all.
Corroded terminals inside the sensor connector are a frequent cause on older GM vehicles, so always inspect the pins before condemning the sensor.
The engine coolant temperature sensor shares its ground with other sensors on some GM platforms, so a bad ground can set multiple codes including P1185.
A stuck-open thermostat can make the engine warm up too slowly, causing the engine control module to flag the temperature sensor circuit as implausible.
After replacing the sensor, clear the code and verify the temperature reading on a scan tool rises smoothly to normal operating temperature during a test drive.

Can I keep driving with P1185?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads or long trips because incorrect temperature data can cause poor fuel economy, overheating, or cooling fan failure. If the temperature gauge shows overheating or the engine runs poorly, stop driving and have it towed.

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.