DTC 15

Code 15 Chart:

Coolant Temperature Sensor Wiring Diagram:

CIRCUIT DESCRIPTION:

The Coolant Temperature Sensor (CTS) uses a thermistor to control the signal voltage at the ECM. The ECM applies a voltage on circuit 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore, ECM terminal "Y18" voltage will be high. 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 ECM terminal "Y18."

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

1. A Code 15 will set if the signal voltage indicates a coolant temperature above 140°C (285°F).

2. This test will determine if circuit 410 is shorted to ground which will cause the conditions for Code 15.

DIAGNOSTIC AIDS:

Check harness routing for a potential short to ground in CKT 410. After the engine is started, the temperature should rise steadily to about 90°C, then stabilize when thermostat opens. Refer to INTERMITTENTS in the DIAGNOSIS BY SYMPTOM - NO CODES SECTION.
Verify that engine is not overheating and has not been subjected to conditions which could create an overheating condition (i.e. overload, trailer towing, elevated terrain, heavy stop and go traffic, etc.). The "TEMPERATURE TO RESISTANCE VALUES" scale 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.