DTC 15

Code Chart 15:

Coolant Temperature Sensor Circuit:

CIRCUIT DESCRIPTION:

The coolant temperature sensor is a thermistor (a variable resistor that changes along with coolant temperature) in series with a fixed resistor in the ECM. The ECM applies 5.0 volts to the sensor. The ECM monitors the voltage across the coolant temperature sensor and converts it into a temperature reading. When the engine is cold, the sensor resistance is high, therefore, the ECM will see high signal voltage. As the engine warms, the sensor resistance becomes less, and the ECM will read a low voltage input. Code 15 will set if the following condition is met for at least 3 seconds; Voltage input at the ECM indicates a coolant temperature above 136°C (276°F).

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

1. This test simulates Code 14. If the ECM stores Code 14, the ECM and its wiring are OK and the coolant temperature sensor is faulty. If Code 15 resets, the coolant temperature sensor is OK and the wiring to the ECM or the ECM is faulty.

DIAGNOSTIC AIDS:

After engine is started the temperature should rise steadily to about 95°C (203°F) then stabilize when thermostat opens.

Verify that engine is not overheating and has not been subjected to conditions which could create an overheating condition (i.e. overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.). When replacing the coolant temperature sensor the "Temperature to Resistance Value" scale on the chart may be used to test the coolant temperature sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.