Owner's Problem Description
The owner of a 1997 Buick Skylark reports that both the EGT light and check engine light are illuminated on the dashboard. The issue seems to arise intermittently, particularly during operation after the vehicle has warmed up. The owner has not indicated any previous repairs related to the engine temperature or exhaust systems. The vehicle currently runs but the warning lights are concerning.
Professional Technical Analysis
The 1997 Buick Skylark is equipped with an engine temperature sensor (ETS) that monitors the engine's operating temperature and relays this information to the Powertrain Control Module (PCM). When the EGT light illuminates, it indicates that the PCM has detected an abnormal temperature reading, suggesting that the engine is either overheating or that there is a fault in the sensor circuit. Typical causes include sensor failure, wiring issues, or a malfunctioning PCM. The normal operating temperature for this vehicle should be around 195°F to 220°F. A check of the EGT sensor should reveal whether it is providing accurate readings, as improper voltage output (typically 0.5V to 4.5V depending on temperature) can cause the EGT light to activate. Given the vehicle's age and mileage, around 100,000 miles, it is reasonable to suspect wear or degradation in the wiring harness or connectors, which could introduce resistance and affect sensor performance. Additionally, previous repair history or lack thereof should be reviewed to ascertain whether any related components have been replaced. This condition may also pose safety concerns if it leads to engine overheating, which could result in severe engine damage.
Possible Causes
Most common causes (ordered by frequency):
- Engine Temperature Sensor (ETS) Failure: The ETS may have degraded over time, causing inaccurate temperature readings. Typically, the sensor should provide a voltage output that varies with temperature, ideally between 0.5V and 4.5V. A malfunctioning sensor may fail to reflect actual engine temperature, leading the PCM to trigger the EGT light. Replacement of the ETS is typically required when diagnostic tests confirm sensor failure. In vehicles with over 100,000 miles, it is not uncommon for these sensors to fail due to thermal fatigue or corrosion. - Illuminated EGT light, potential stored codes related to temperature sensor malfunction, voltage readings from the ETS significantly outside normal range.
- Wiring Issues: Damaged or corroded wiring in the engine bay can lead to intermittent signals to the PCM, which may cause the EGT light to turn on. Visual inspection for any frayed wires, loose connections, or corrosion at the sensor connector is recommended. Testing the continuity of the wiring harness and checking for shorts to ground can help identify issues that may not be immediately apparent. - Corroded connectors, visual signs of wear on wiring, intermittent voltage readings indicating possible connectivity issues.
- PCM Malfunction: In rare cases, the Powertrain Control Module itself may malfunction, leading to incorrect interpretation of sensor data. If both the EGT and check engine lights are illuminated together, this could indicate a deeper issue within the PCM. Diagnostic testing should include checking for fault codes related to the PCM and ensuring software updates are installed as needed. - Presence of multiple fault codes, potential software issues indicated by manufacturer updates, abnormal behavior in other engine control parameters.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial OBD-II Scan: Start with a full OBD-II scan using a professional scanner or the GeekOBD APP to retrieve stored trouble codes. Pay close attention to any codes related to the engine temperature sensor or PCM. Freeze frame data may provide insights on the conditions under which the EGT light activated.
- STEP 2 - Inspect Engine Temperature Sensor: Physically locate the engine temperature sensor under the hood on the driver’s side at the cylinder head. Check the connector for corrosion or damage. Use a multimeter to check the sensor's resistance at various temperatures to ensure it operates within the specified range.
- STEP 3 - Wiring Inspection: Inspect the wiring harness connected to the temperature sensor for any signs of wear, fraying, or corrosion. Perform continuity tests to identify any breaks or shorts in the wiring, which could affect sensor performance.
- STEP 4 - PCM Diagnostic Check: If no issues are found with the sensor or wiring, proceed to check the PCM for fault codes and ensure that it is functioning correctly. Verify that any software updates have been applied as recommended by the manufacturer.
