OBDII trouble codes P0118 and P0119 are related to the Engine Coolant Temperature (ECT) sensor. These codes indicate that the Powertrain Control Module (PCM) has detected an issue with the signal from the ECT sensor. Specifically, P0118 means “Engine Coolant Temperature Circuit High Input,” while P0119 indicates “Engine Coolant Temperature Circuit Intermittent.”
Understanding OBDII Codes P0118 and P0119
- P0118 – Engine Coolant Temperature Circuit High Input: This code is set when the PCM reads an abnormally high voltage signal from the ECT sensor circuit. This high voltage suggests a potential open circuit, a short to voltage, or a faulty sensor incorrectly reporting a very low coolant temperature (even though voltage is inversely related to temperature in many ECT sensors, “high input” refers to the signal voltage).
- P0119 – Engine Coolant Temperature Circuit Intermittent: This code is triggered when the PCM detects an unstable or fluctuating signal from the ECT sensor circuit. This intermittency could be due to loose connections, wiring issues, or a sensor that is failing sporadically.
Symptoms of P0118 and P0119
When OBDII codes P0118 or P0119 are displayed, you may experience several symptoms, including:
- Check Engine Light (MIL) illumination: This is the most common and immediate symptom.
- Inaccurate Temperature Gauge Reading: The temperature gauge on your dashboard might display an unusually low reading or fluctuate erratically.
- Poor Engine Performance: In some cases, the PCM might use a default value for engine temperature, which can lead to issues like poor fuel economy, rough idling, or difficulty starting, especially in cold weather.
- Engine overheating (potentially): Although less common with P0118/P0119 directly, incorrect temperature readings can indirectly lead to overheating if the cooling system isn’t managed properly due to faulty sensor data.
Causes of P0118 and P0119
Several factors can cause P0118 and P0119 codes to be set:
- Faulty ECT Sensor: The sensor itself might be defective and providing incorrect readings.
- Wiring Issues: Damaged, corroded, or loose wiring in the ECT sensor circuit can lead to high resistance (P0118) or intermittent signals (P0119). This includes connectors and wiring harnesses.
- Open Circuit: A break in the wiring to the ECT sensor can cause a “high input” reading as the signal is disrupted (P0118).
- Short to Voltage: The ECT sensor circuit might be shorting to a voltage source, causing an abnormally high signal (P0118).
- PCM Issues (less likely): In rare cases, a problem within the PCM itself could misinterpret or incorrectly process the ECT sensor signal.
- Coolant Level/Thermostat Issues (Indirectly): While not direct causes of P0118/P0119, very low coolant levels or thermostat malfunctions can sometimes indirectly affect ECT sensor readings or circuit behavior.
Diagnosing and Fixing P0118 and P0119
Troubleshooting these codes typically involves a systematic approach:
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Visual Inspection: Check the ECT sensor and its wiring for any obvious damage, corrosion, or loose connections. Pay close attention to the connector at the sensor and along the wiring harness.
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Scan Tool Verification: Use an OBDII scan tool to confirm the presence of codes P0118 and/or P0119 and check for any other related codes. Monitor the ECT sensor reading on the scan tool to see if it is abnormally high or fluctuating.
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Wiring and Circuit Testing: Use a multimeter to test the ECT sensor circuit for continuity, shorts to voltage, and shorts to ground. Refer to a vehicle-specific wiring diagram for proper test points and expected values.
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Sensor Testing: Test the ECT sensor itself using a multimeter to measure its resistance. Compare the readings to the manufacturer’s specifications at different temperatures.
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Component Replacement:
- If the sensor is found to be faulty, replace the ECT sensor.
- Repair any wiring issues, including repairing or replacing damaged wires or connectors.
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Clear Codes and Retest: After repairs, clear the OBDII codes using a scan tool and test drive the vehicle to see if the codes return. Monitor the ECT sensor reading again with the scan tool to ensure it is now functioning correctly.
Conclusion
OBDII codes P0118 and P0119 signal potential problems within the Engine Coolant Temperature sensor circuit. Proper diagnosis, including visual inspections and circuit testing, is crucial for identifying the root cause. Addressing these codes promptly will help ensure accurate engine temperature readings, optimal engine performance, and prevent potential engine damage. If you are not comfortable performing these diagnostic steps, it is recommended to seek assistance from a qualified automotive technician.
Note: While this article focuses on P0118 and P0119, if you are experiencing code P0128 (mentioned in the original article), that typically points to a thermostat issue preventing the engine from reaching operating temperature quickly enough.
