Coolant Temperature Sensor/Switch (For Computer): Testing and Inspection

Engine Coolant Temperature Sensor Circuit:

Failure Modes
DTC 22 will set if either of the following conditions are met for at least 0.50 seconds:

1. Voltage input at the ECM indicates a very low ECT.

2. Voltage input at the ECM indicates a very high ECT.

Test Description:
1. This checks for an open or short to ground in the WHT wire between the ECM and ECT sensor and for a faulty ECM.

2. This checks for an open in the BRN wire between the ECM and the ECT sensor and for a faulty ECM.

3. This determines if the problem is a faulty ECT sensor or ECM.

Diagnostic Aids:
Verify that the engine is not overheating and has not been subjected to conditions which could create an overheating condition (i.e., overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.).

A "shifted" (mis-scaled) sensor could result in poor driveability complaints. Measure the resistance of the ECT sensor according to the diagnostic aids chart on the diagnostic chart. If DTCs 24, 31 and 41 are also set, problem is open sensor ground circuit.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.