DTC 15

Code 15 - Coolant Sensor Circuit (Signal Voltage High):

Wiring Diagram For Code 15 - Coolant Sensor Circuit:

CODE 15 - COOLANT SENSOR CIRCUIT (SIGNAL VOLTAGE HIGH)


Circuit Description:

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

As the coolant warms, the sensor resistance becomes less, and the voltage drops. At normal operating temperature, the voltage will measure about 1 to 1.5 volts at the ECM terminal C10.

Code 15 will set if all of these conditions are met:

^ Signal voltage indicates a coolant temperature less than -35~C (-31~F).

Coolant temperature is one of the inputs used to control:

^ Fuel delivery.
^ Spark Timing (EST)
^ Idle (IAC)
^ Converter Clutch (TCC)
^ Canister Purge (CCP)
^ EGR


If the coolant CKT 410 opens with the ignition off, the ECM will see -32~C (-26~F) and deliver fuel for this temperature. If the actual temperature is above approx. -7~C (20~F), the engine will not start due to the rich mixture, unless "Clear Flood" is used by fully depressing the accelerator. Engine will start using "Clear Flood" (which is Wide Open Throttle). However, "SERVICE ENGINE SOON" light will not come on, and code will not be stored until engine has run for one minute.

Test Description:

1. Checks to see if code was set as a 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.