Code 15 - Coolant Sensor Circuit Open
The Coolant Temperature Sensor uses a thermistor to control the signal to the ECM. The ECM applies a voltage on circuit 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, and the ECM will set a high signal voltage. As the engine warms, the sensor resistance becomes less, and voltage drops. At normal engine operating temperature, the voltage will measure 1-1.5 volts at the ECM term. "4" (2.0L-"C10"). Coolant temperature is used to control fuel delivery, engine timing (EST), idle (IAC) and converter clutch (TCC) (2.0L- Add Pulsair and EGR). Code 15 means the ECM has seen the coolant temperature at less than -35°F (-31°C) for 4 seconds, 1 minute after engine start. If circuit 410 opens with the ignition "OFF," the ECM will supply a mixture that is full rich. The only way to start the engine will be to "Clear Flood" by going to Wide Open Throttle. Code 15 will not set until engine has run for 1 minute.
- If voltage is above 4 volts, the ECM and wiring are OK.
- If location of sensor makes it hard to check, disconnect Black ECM connector and check resistance between connector terms. "4" and "11" (2.0L-"C10" and "A11").