Engine Oil Temperature Sensor Circuit Low Input
The P0197 code indicates that the Engine Control Module (ECM) has detected a voltage signal from the engine oil temperature (EOT) sensor that is lower than the expected range. This typically means the sensor's resistance is too low, often due to a short circuit to ground, a faulty sensor, or wiring issues. The EOT sensor is a thermistor that changes resistance with temperature; low voltage suggests a high temperature reading or a short. This can affect engine performance and trigger the check engine light.
1. Most Common Causes
- Faulty or deteriorated engine oil temperature (EOT) sensor
- Sensor circuit wiring shorted to ground
- Corroded, damaged, or moisture-contaminated sensor connector
- Excessive internal resistance in wiring or connectors
- Intermittent harness failure near heat sources or vibration points
- Rarely, internal ECM/PCM failure (diagnosis by exclusion)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine performance issues (rough idle, hesitation)
- Inaccurate oil temperature reading on gauge
- Possible limp mode activation
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for other related codes.
Step 2: Visually inspect the EOT sensor connector and wiring for damage, corrosion, or shorts.
Step 3: Measure the sensor resistance with a multimeter; compare to specifications (typically 100k-1M ohms at cold, lower when hot).
Step 4: Check for voltage at the sensor connector (usually 5V reference from ECM). If voltage is low, check for shorts to ground.
Step 5: If sensor and wiring are okay, test the ECM output or replace the sensor.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally not recommended to drive long distances as the ECM may use a default temperature value, potentially causing poor performance or increased wear. Short trips to a repair shop are usually okay.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150, including parts (sensor $20-$60) and labor (0.5-1 hour). Diagnostic fees may add $50-$100.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.