Choke Relay: Testing and Inspection

Connector M21:

To test the Electric Choke Relay, located in the engine compartment on the passenger side firewall, proceed as follows.

1. Locate the carburetor connector (connector M21) and insert a pin to contact the auto choke heater terminal (terminal 5). Attach a voltmeter, with the ignition "off" the reading should be 0 volts.
2. Turn the ignition "on", the reading should remain 0 volts (the relay is powered open by the ECU providing a ground).
3. Start the engine while observing the voltmeter, during cranking the voltmeter should read 0 volts.
4. If the engine coolant temperature is below 18°C (64°F), after cranking the voltmeter should continue to read 0 volts for approximately 80 seconds. At the end of this time the reading should increase to battery voltage (the ECU removes the ground and the relay closes), and remain there until the engine approaches operating temperature.
5. If the engine coolant temperature is above 18°C (64°F), after cranking the voltmeter should read battery voltage (the ECU removes the ground and the relay closes), and remain there until the engine approaches operating temperature.
6. If the Relay does not open at the proper time, test pin A-4 on the ECU connector, to determine if the ECU is providing a ground.
7. If there is continuity to ground at pin A-4, and the Relay has still not opened, then the relay is faulty.
8. If there is NO continuity to ground, then either the ECU, the wiring harness, or the coolant temperature sensor is at fault.
9. Test the coolant temperature sensor signal to the ECU before replacing the ECU.