Owner's Problem Description
The vehicle owner has a 1999 Saturn SL that had a newer transmission installed. After replacing the transmission fluid temperature sensor, the warning light for the sensor remains illuminated. The car is running well, and the transmission operates normally, but the persistent warning light indicates an unresolved issue. The owner is seeking to understand the underlying problem despite having changed the sensor.
Professional Technical Analysis
The 1999 Saturn SL is equipped with a 1.9L engine and an automatic transmission, and is estimated to have around 150,000 miles. The owner reports a persistent warning light for the transmission fluid temperature sensor (DTC P0713) despite having replaced the sensor. This code indicates an issue with the sensor signal, which can arise from several factors including wiring problems or connector issues. The transmission fluid temperature sensor is crucial for the PCM to accurately measure fluid temperatures, which in turn affects shift timing and overall transmission performance. Given the high mileage, it's also possible that wiring harness degradation or a poor connection at the sensor is causing the code to trigger. Additionally, the vehicle's history with previous repairs can provide insight into whether the issue has been ongoing or a new occurrence. A visual inspection of the wiring and connectors is recommended, as well as verification of the new sensor's resistance values (typically around 1-5k ohms depending on temperature). If the wiring appears intact, further testing with an oscilloscope may be necessary to assess signal integrity. Given the potential for cascading failures in sensor systems, addressing this issue promptly is advised to maintain vehicle reliability.
Possible Causes
Most common causes (ordered by frequency):
- Faulty Connector or Wiring: Often, issues with the transmission fluid temperature sensor are related to damaged wiring or a poor connection at the connector. Given the age of the vehicle, wiring insulation may deteriorate, leading to intermittent signal issues. Inspect the wiring harness for any visible wear or damage, and ensure that the connector pins are clean and making good contact. A continuity test should be performed to confirm that there are no breaks in the wiring. Voltage at the sensor should be around 5V, and the signal to the PCM must fluctuate based on the fluid temperature. - Persistent P0713 code, visual inspection of wiring shows signs of wear, continuity test on sensor wiring shows intermittent connectivity.
- Incorrect or Defective Replacement Sensor: Aftermarket sensors may not always meet OEM specifications, leading to potential compatibility issues. If the replacement sensor is not functioning correctly, it may continuously trigger the warning light. Verify the part number with GM specifications and ensure that a quality sensor is installed. Testing the resistance of the sensor with a multimeter can confirm its functionality; it should typically read 1-5k ohms based on temperature. - Replacement sensor matches part number but still triggers P0713 code, multimeter test shows incorrect resistance values.
- PCM Programming Issue: In some cases, the PCM may require reprogramming after a transmission replacement or sensor change. If the PCM is not calibrated to recognize the new sensor, it may still indicate a fault. Checking for any software updates or recalibrations can resolve this issue. Accessing the PCM using a professional scan tool may reveal additional diagnostic information. - PCM does not recognize new sensor after installation; no software updates conducted, scan tool shows calibration mismatch.
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 - OBD-II Code Retrieval: Begin by using a professional OBD-II scanner or the GeekOBD APP to retrieve the stored codes. This will confirm the presence of P0713 and allow for examination of freeze frame data to analyze conditions at the time the code was set. The GeekOBD APP can provide valuable live data monitoring to help identify patterns or intermittent issues during a test drive.
- STEP 2 - Visual Inspection of Wiring and Connectors: Conduct a thorough visual inspection of the wiring harness leading to the transmission fluid temperature sensor. Look for signs of wear, fraying, or corrosion at the connector. Also, check for any loose connections that could affect signal integrity. If any issues are found, repair or replace the affected wiring or connectors as necessary.
- STEP 3 - Sensor Testing: After ensuring the wiring is intact, test the new transmission fluid temperature sensor using a multimeter. Measure the resistance of the sensor; it should fall within the specified range of 1-5k ohms depending on the temperature. If the readings are outside of this range, the sensor may be faulty and should be replaced again. Also, check the voltage output from the sensor while the vehicle is running; it should provide a fluctuating signal based on transmission fluid temperature.
- STEP 4 - PCM Calibration Check: If the wiring and sensor are functioning correctly, consider checking for any PCM software updates or recalibrations. Access the PCM using a professional scan tool to ensure it is configured to recognize the new sensor. If necessary, perform a recalibration or update the PCM software per manufacturer specifications.
