What is CID 621:
CID 621 refers to an issue with the transmission system, specifically related to the transmission fluid temperature sensor. The ECM detects that the signal from the sensor is outside of the expected range, which can affect transmission performance and cause overheating.
Why This Happens:
- Faulty transmission fluid temperature sensor.
- Shorted or damaged wiring in the sensor circuit.
- Loose or corroded sensor connectors.
- Malfunctioning transmission system affecting fluid temperature.
- ECM misinterpretation of the sensor’s data.
How to Fix It:
- Inspect the transmission fluid temperature sensor for malfunction.
- Test the sensor’s voltage and resistance to verify it’s within specifications.
- Check wiring and connectors for damage or corrosion.
- Replace the faulty sensor if necessary.
- Inspect the transmission system for overheating or poor performance.
How to Avoid It Before It Happens:
- Regularly inspect the transmission fluid temperature sensor and wiring.
- Perform routine transmission system maintenance.
- Keep connectors clean and corrosion-free.
- Perform diagnostic checks to monitor transmission health.
- Clue’s fleet management software helps monitor transmission systems and prevent overheating or performance issues.
