DTC 15

CIRCUIT DESCRIPTION
The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the Engine Control Module (ECM). The ECM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage.

As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature the voltage will measure about 1.5 to 2.0 volts at the ECM terminal C10.

Coolant temperature is one of the inputs used to control:
^ Fuel delivery.
^ Engine Spark Timing (EST)
^ Idle (IAC)
^ Convertor Clutch (TCC)
^ Canister Purge (CCP)
^ EGR
^ Cooling fan

Code 15 will set if:
^ Signal voltage indicates a coolant temperature less than -44°C (-47°F) for 3 seconds.

CHART TEST DESCRIPTION
1. Checks to see if code was set as result of hard failure or intermittent condition.

2. This test simulates a code 14. If the ECM recognizes the low signal voltage and sets a code 15, the ECM and wiring are OK.

3. If code 15 repeats, the problem is an open CKT 410, 452, a poor connection at the ECM or sensor, or a faulty ECM.