Powertrain Controls - ECM/PCM

DTC 15 Chart Engine Coolant Temperature Sensor:

Engine Coolant Temperature Sensor Wiring Diagram:

CIRCUIT DESCRIPTION
The engine coolant temperature sensor uses a thermistor to control the signal voltage to the Electronic 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. Engine coolant temperature is one of the inputs used to control:

- Fuel delivery.
- EVAP canister purge.
- Ignition Control (IC).
- Exhaust Gas Recirculation (EGR).
- Idle Air Control (IAC).
- Cooling fan operation.
- Torque Converter Clutch (TCC).

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart:

1. DTC 15 will set if engine coolant temperature voltage indicates a coolant temperature less than -49.5° C (-56.2° F).
2. This test simulates a DTC 14. If the ECM recognizes the low signal voltage, (high temperature) and the "Scan" reads 130° C (266° F), the ECM and wiring are OK.
3. This test will determine if CKT 410 is open. There should be 5 volts present at sensor connector if measured with a Digital Volt Meter (DVM).

DIAGNOSTIC AIDS
After engine is started the temperature should rise steadily reach normal operating temperature, then stabilize when thermostat opens. A faulty connection, or an open in CKT 410 or 470 will result in a DTC 15.

If DTC 21 is also set, check CKT 470 for faulty wiring or connections. Check contacts and Engine Coolant Temperature sensor for good connection.

The "Temperature To Resistance Value" scale may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor, which may result in driveability complaints.