Circuit/System Testing

Ignition OFF, disconnect the engine coolant temperature (ECT) sensor.
Ignition ON, verify that the ECT sensor parameter is at -40°C (-40°F).
- If greater than the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.
CAUTION: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.

NOTE: The control module or the sensor may be damaged if the circuit is shorted to B+.
Test for less than 1 volt between the low reference circuit terminal 2 and ground.
- If greater than the specified value, test the low reference circuit for a short to B+. If the circuit tests normal, replace the ECM.
Ignition OFF, remove the fuse that supplies B+ to circuit terminal C2-56 of the ECM.
Test for less than 5 ohms between the low reference circuit terminal 2 and ground.
- If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
Install the fuse that supplies B+ to circuit terminal C2-56 of the ECM.
NOTE: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.
Ignition ON, connect a 3A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the scan tool ECT sensor parameter is greater than 142°C (288°F).
- If less than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
If all circuits test normal, test or replace the ECT sensor.