Diagnostic Aids

When DTC P0128 is set, a skewed ECT sensor or a stuck-open thermostat is indicated.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside the insulation.

Check for a poor connection or damaged ECM harness. Inspect the ECT sensor signal circuit and ground circuit terminals for the following conditions:

• Improper mating
• Broken locks
• Improperly formed
• Damaged terminals
• Poor terminal-to-wire connection
• Damaged harness

Perform an Intermittents test. If connections and harness check OK, monitor a digital voltmeter connected between ECT sensor signal circuit and ground circuit terminals while moving related connectors and wiring harness. If a fault is induced, the resistance reading will change. This may help to isolate the location of the malfunction.

Use the Temperature vs. Resistance table to evaluate the possibility of a skewed sensor.