The thermal engine room switch, essentially an underhood temperature switch, is only used on carbureted models as part of the feedback carburetor system.
The thermal engine room switch provides temperature information to the ECM for driveability. The switch opens and closes depending on the engine compartment temperature. The switch is closed when the air in the engine compartment is cold, and opens when the engine compartment air warms to above 67°F (19.5°C). The ECM monitors the switch circuit, and knows the underhood air is warmed up when the circuit registers infinite resistance (the switch is open).
The switch is mounted on the right-hand side of the firewall, just above the HAC switch.
- Detach the wiring harness connector from the switch, then attach an ohmmeter to the terminals of the switch.
Check the resistance of the switch.
- If the ambient air temperature is below 44°F (7°C), the switch should show 0 ohms (the switch contacts are closed).
- If the air temperature is above 67°F (19.5°C), the switch should show infinite resistance (no continuity).To simulate colder temperatures during warm weather, place the sensor in the freezer for a few minutes, then measure the sensor resistance.
- If the switch resistance values were not as specified, or if the switch exhibited any ohm value other than 0 or infinity, the switch is defective and should be replaced with a new one.
REMOVAL & INSTALLATION
- Disconnect the negative battery cable.
- Disengage the wiring harness connector from the switch.
- Loosen the mounting bolts, and remove the switch from the firewall.
- Position the switch on the firewall, then install and tighten the mounting bolt(s) securely.
- Reattach the wiring harness connector to the switch.
- Connect the negative battery cable.