The temperature gauge itself is driven by a temperature sensor, usually a thermistor or other type of sensor that changes resistance based on temperature. This sensor is located in the engine block or cylinder head. If the gauge isn't working, the most likely culprit is a failed temperature sensor, a faulty gauge itself, or a problem in the wiring between the sensor and the gauge cluster.
The cooling fan is typically controlled by a separate cooling fan relay and/or a computer module (PCM or ECM) that monitors the coolant temperature via a different sensor (it might be a *separate* temperature sensor, or the same one used by the gauge, but a failure in one doesn't automatically mean failure in the other). The fan running might indicate the PCM is getting a signal about high coolant temperature, even if your gauge isn't showing it.
The check engine light comes on when the Powertrain Control Module (PCM) detects a problem. This could be related to the cooling system (like a low coolant level sensor or a problem with the coolant temperature sensor circuit), but it could also be completely unrelated. You'll need to use an OBD-II scanner to read the diagnostic trouble codes (DTCs) stored in the PCM to determine the exact reason for the check engine light. A 1993 model may require a scan tool specific to that year.
In summary:
* Temperature Gauge Not Working: Faulty temperature sensor, gauge itself, or wiring problem.
* Cooling Fan Working: The system is likely detecting high coolant temperature, possibly accurately, even if the gauge is malfunctioning.
* Check Engine Light On: Requires an OBD-II scan to determine the specific code(s). This could be related to the cooling system, but it could be something else entirely.
To diagnose the issue, you should:
1. Get the check engine light codes read: This is the most crucial first step.
2. Test the coolant temperature sensor: A multimeter can check its resistance readings against specifications (look this up in a repair manual for your specific car).
3. Check the wiring: Look for broken or corroded wires between the sensor and the gauge, and between the sensors and the PCM.
4. Check the gauge itself: This is less likely, but possible. It's usually only diagnosed by process of elimination.
Without the diagnostic trouble codes, any further troubleshooting is largely guesswork. Start with that OBD-II scan!
