Code
P1119
HUMMER
P — Powertrain
ECT Signal Out-Of-Range With TFT Sensor
AI status
Completed
Completed
100%
Causes
- Damaged or corroded ECT sensor connector or wiring
- Open or shorted ECT sensor circuit
- Faulty ECT sensor (thermistor)
- Poor ground or lost 5 V reference to sensor
- Intermittent or corroded TFT sensor connection or cross-talk between circuits
- PCM/ECM internal fault (less common)
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Incorrect coolant temperature gauge or temp reading in cluster
- Engine running rich/lean, hard start, or poor idle when cold
- Cooling fan not operating properly or running continuously
- Possible transmission shift issues if PCM uses TFT data for logic
What to check
- Scan for stored codes and freeze frame data; note related transmission or engine codes
- Inspect ECT and TFT sensor connectors for corrosion, bent pins, water intrusion, or damage
- Visually inspect wiring harness for chafing, pinches, heat damage, or insulation breaches between ECT and nearby circuits
- Backprobe ECT sensor signal, reference (5 V) and ground with key on; verify proper voltages
- Measure ECT sensor resistance at known coolant temperatures and compare to expected thermistor curve
- Compare ECT and TFT temperature readings with actual measured temperatures (infrared thermometer or probe) using a live-data tool
Signal parameters
- Sensor type: ECT — NTC thermistor (resistance falls as temperature rises)
- Electrical interface: 0–5 V signal; 5 V reference and chassis ground commonly used
- Typical operating temps: -40 °C to +150 °C sensor capability; normal engine operating 80–110 °C
- Expected live-data ranges: ECT and TFT should read near ambient at cold cranking and climb to normal operating temp; unstable, pegged, or out-of-range voltages indicate fault
- Resistance behavior: high ohms at cold, low ohms when hot (compare to OEM chart)
Diagnostic algorithm
- Retrieve freeze frame and all stored/active codes. Note timestamps and related DTCs (especially ECT/TFT/PCM codes).
- Perform visual inspection of ECT and TFT sensor connectors and wiring. Repair any corrosion, damaged pins, or insulation problems. Secure connectors and harness routing.
- With ignition ON (engine off), backprobe ECT connector: verify 5 V reference present, good ground, and sensor signal voltage (should vary with temperature). If reference or ground missing, trace to PCM fuse and ground point.
- Measure ECT sensor resistance at engine cold and warm (engine off). Compare resistance to OEM thermistor table. Replace sensor if resistance not within expected range.
- If sensor readings electrical are good, compare live-data ECT and TFT temperatures to actual temperatures measured with a thermometer or temperature probe at the thermostat housing and transmission fluid. Look for inconsistent or implausible values.
- If wiring or connectors suspect, repair or replace harness section. If signal intermittently fails during wiggle testing, repair routing/clips and replace connector as needed.
- If wiring and sensors test good, consider PCM input circuit fault; verify wiring continuity to PCM and check for short to other circuits. Replace PCM only after exhausting harness and sensor diagnostics.
- Clear codes, perform functional test or road test, and re-scan to confirm code does not return.
Likely causes
- Corroded/loose connector at ECT sensor
- Short to voltage or ground in ECT harness
- Faulty ECT sensor (NTC thermistor)
- Loss of reference voltage or ground at sensor harness
Fault status
Status
PCM detected ECT sensor signal outside expected range while TFT sensor present; diagnostic trouble code P1119 set.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Repair manuals
Manual library for HUMMER
138
Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
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