The CTS sends a signal to the gauge cluster. If the sensor is faulty (shorted or otherwise malfunctioning), it could be sending a signal indicating extremely high temperatures.
Here's a breakdown of why it's *unlikely* to be other issues and what you should do:
* Not overheating: The engine isn't running, so it's impossible for the coolant to overheat.
* Wiring issue: A short circuit in the wiring leading to the CTS could also cause this.
* Gauge Cluster Problem: While less likely, a faulty temperature gauge in the instrument cluster itself could display an incorrect reading.
What to do:
1. Check the coolant level: While unlikely to be related to the immediate high reading, low coolant is a serious issue that needs attention.
2. Replace the Coolant Temperature Sensor (CTS): This is the most probable culprit. It's a relatively inexpensive and easy-to-replace part. You can find diagrams and instructions online specific to your 1991 Jetta model.
3. Check the wiring: Inspect the wiring harness leading to the CTS for any damage, shorts, or loose connections.
4. Test the gauge cluster (advanced): This requires more technical expertise and testing equipment. If replacing the CTS and checking wiring doesn't solve the problem, this is the next step.
Important Note: While the immediate high reading suggests a sensor or wiring issue, always be cautious with overheating-related problems. If you ever see the temperature gauge rising while the engine is running, turn off the engine immediately to prevent serious engine damage.
