DTC 15

The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 37 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage on CKT 37.

As the engine warms, the sensor resistance becomes less, end the voltage drops. At normal engine operating temperature the voltage will measure about 1 to 1.5 volts at ECM terminal M2-10.

Code 15 will set if:

^ Signal voltage indicates a coolant temperature less than -38.5°C (-37.3°F) for 10 seconds after engine has run more than 1 minute.

Coolant temperature is one of the inputs used to control:

^ Fuel delivery
^ Canister purge control
^ Electronic spark timing (EST)
^ AIR control
^ Idle air control (IAC)
^ EGR control
^ Turbocharger wastegate control
^ EGR system diagnostic

If the coolant CKT 37 opens with the ignition "OFF", the ECM will see -40°C (-40°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. The engine will start using "Clear Flood" (which is Wide Open Throttle). However, the "CHECK ENGINE" light will not come "ON", and Code 15 will not be stored, until the engine has run for one minute.

1. If voltage between harness connector terminals M2-10 and M2-18 is above 4 volts, the ECM and wiring are OK.
2. If location of sensor makes resistance hard to check, disconnect ECM connector and check resistance between connector terminals M2-10 and M2-18.