Code
P0116
HUMMER
P — Powertrain
Engine Coolant Temperature (ECT) Sensor Performance
AI status
Completed
Completed
100%
Causes
- Faulty/contaminated ECT sensor (thermistor)
- Open or shorted wiring between ECT sensor and PCM
- Corroded/loose connector or poor pin contact at sensor or PCM
- Incorrect coolant level or air in cooling system causing false readings
- Stuck thermostat or cooling system problems altering temperature response
- PCM fault or internal reference/pull‑up circuit failure (less common)
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated with P0116 stored
- Incorrect temperature gauge reading (very low, very high, or erratic)
- Hard cold or hot starting and poor driveability during warm‑up
- Longer-than-normal open‑loop operation and poor fuel economy
- Radiator fan operation abnormal (on/off at wrong times) or overheating warning lamp
- Increased emissions or failed emissions test
What to check
- Read and record freeze‑frame data and pending codes with a scan tool
- Monitor live ECT data during cold start and warm‑up; compare to ambient and expected warm‑up curve
- Visually inspect sensor, connector and wiring for corrosion, damage, or loose terminals
- Confirm correct coolant level and absence of large air pockets in cooling system
- Backprobe ECT signal and ground with multimeter/scan tool while engine warms up
- Measure sensor resistance at known temperatures (cold and hot) and compare to expected values
Signal parameters
- ECT type: negative temperature coefficient (NTC) thermistor (resistance falls as temperature rises)
- Typical resistance examples (generic guidance; varies by sensor): ~2–5 kΩ at ~20°C, ~200–500 Ω at ~80°C, ~100 Ω at ~100°C; very high resistance (>50–100 kΩ) at very cold temps or open circuit
- Typical signal voltage at PCM (with pull‑up): ~0.5–4.5 V depending on temperature (low voltage = hot, high voltage = cold)
- Short to ground: signal near 0 V; short to battery: signal near battery voltage (~5 V or ~12 V depending on circuit)
- Expected change: steady, smooth change in resistance/voltage with temperature increase; rapid jumps or no change indicate fault
Diagnostic algorithm
- Retrieve MIL, freeze frame and all stored codes; note ambient temp and operating conditions.
- Visually inspect sensor, connector, and harness for corrosion, pin damage, or disconnected wires; repair any obvious issues.
- Confirm coolant level and properly burp system if air suspected; verify thermostat operation and correct coolant flow.
- With a scan tool, monitor ECT live data during cold start and warm‑up; note whether reading changes smoothly and reaches normal operating temperature.
- Backprobe the signal and ground at the sensor with a DVOM/scan tool; check signal voltage behavior while warming. Verify reference voltage present if applicable.
- Remove sensor and measure resistance at engine cold and warmed states (or compare to manufacturer's resistance table). Replace sensor if out of expected range or intermittent.
- Check continuity and resistance of harness between sensor and PCM; inspect for shorts to 5V or ground and repair wiring as needed.
- If harness and sensor test good, swap in a known‑good ECT sensor or temporarily substitute with OEM spec part and retest.
- Clear codes and perform road/drive cycle to confirm repair; if P0116 returns with good sensor and wiring, consider PCM input circuit diagnosis or reflash/update per manufacturer guidance.
Likely causes
- Damaged/contaminated ECT sensor
- Corroded connector or bent/broken terminal at sensor harness
- Short to power or short to ground in harness
- Low coolant level or trapped air causing false temp swings
Fault status
Status
MIL ON — P0116 stored. PCM sees ECT sensor signal performance outside expected parameters (erratic, implausible, or out‑of‑range). Further testing of sensor, wiring, cooling system and PCM required before repair.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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