Code
P0197
HUMMER
P — Powertrain
Engine Oil Temperature Sensor Low Voltage
AI status
Completed
Completed
100%
Causes
- Faulty/failed engine oil temperature (EOT) sensor (thermistor)
- Damaged, shorted or open wiring harness between sensor and PCM
- Corroded, bent or loose connector pins at the sensor or PCM
- Poor sensor ground or reference voltage (open/high resistance ground)
- Short to ground in the sensor circuit
- Oil contamination or coolant/oil ingress into connector
Symptoms
- Malfunction Indicator Lamp (MIL) or Check Engine Light illuminated
- Incorrect oil temperature displayed on dash (if equipped) or erratic oil temp readings in scan tool
- Longer warm-up or incorrect closed-loop behavior if ECM uses oil temp for fuel/engine control
- Possible degraded engine performance or shift logic changes on vehicles that use oil temperature for strategy
- Intermittent faults if wiring is damaged
What to check
- Retrieve freeze-frame and live data with a scan tool; record EOT sensor voltage/temperature and compare to ambient/known values
- Visual inspection of the EOT sensor connector and harness for corrosion, bent pins, oil contamination, chafing, or damage
- Wiggle test the harness while watching live data to detect intermittent changes
- Backprobe sensor connector: with ignition ON (engine OFF) measure reference voltage and sensor signal to PCM and check for proper ground
- Measure sensor resistance at the sensor (engine cold) and compare to OEM specification/temperature chart
- Check continuity between sensor signal pin and PCM pin and continuity of sensor ground to chassis/PCM ground
Signal parameters
- Typical sensor signal range: 0–5.0 V to PCM (varies by vehicle)
- Common behavior for thermistor-type EOT sensors: resistance decreases as oil temperature rises (NTC)
- Typical resistance examples (generic reference only): approx. >10 kΩ at near-ambient/cold, a few kΩ at moderate temps, and
- With ignition ON (engine OFF) expect a stable reference voltage (often 5 V or a known reference supplied by PCM) and a sensor signal voltage corresponding to ambient temp
Diagnostic algorithm
- Use a scan tool: read and record freeze-frame data and live EOT sensor voltage/temperature. Note when the code set and any related codes.
- Visually inspect the sensor and connector for oil contamination, corrosion, damaged pins, or wiring damage. Repair as needed.
- With connector connected, backprobe the sensor signal and measure voltage at ignition ON and with engine running. Compare to expected reference (OEM).
- Unplug connector and check for short circuits: measure continuity from the sensor signal wire to ground (should not be shorted) and to battery voltage (should not be shorted to VB unless designed).
- Remove sensor and measure its resistance at ambient. Warm the sensor in known temperature water (cold → hot) and verify resistance changes smoothly with temperature; compare to OEM resistance vs temperature chart.
- Check continuity from sensor signal pin to the PCM pin and from the sensor ground to chassis/PCM ground. Repair any high-resistance connections.
- If wiring and sensor test OK, verify PCM reference voltage and ground at the PCM connector. If PCM outputs incorrect reference or has internal faults, follow OEM procedures for module testing.
- Replace the EOT sensor if it fails resistance/voltage checks or shows no change with temperature. Reconnect, clear codes, and perform a drive cycle to confirm repair.
Likely causes
- Corroded/loose sensor connector pin or harness chafe to ground
- Broken/shorted wire in harness near oil pan or routing path
- Failed EOT sensor (thermistor out of spec)
- High resistance or missing sensor ground due to corrosion or damaged terminal
- Oil contamination inside connector causing low-voltage reading
Fault status
Status
PCM has detected a low-voltage (low input) condition on the engine oil temperature sensor circuit. The signal is below the expected threshold, indicating a possible short to ground, open/low-resistance ground, or faulty sensor.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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