DTC 15

CTS Circuit (Low Temp. Indicated):

Code 15 Wiring Diagram:

CIRCUIT DESCRIPTION:

The coolant temperature sensor uses a thermistor to control the signal voltage at the ECM. The ECM applies a voltage on GRAY/WHITE wire to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore, ECM terminal "A14" 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 "A14." Coolant temperature is one of the inputs used to control:

^ Fuel delivery.
^ Engine Spark Timing (EST).

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

1. Code 15 will set if:

^ Signal voltage indicates a coolant temperature above 136°C (276°F) for 3 seconds.

2. This test will determine if GRAY/WHITE wire is shorted to ground which will cause the conditions for Code 15.

DIAGNOSTIC AIDS:

Check harness routing for a potential short to ground in GRAY/WHITE wire circuit. After engine is started, the temperature should rise steadily to about 90°C 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.). The "Temperature To Resistance Value" scale at the right may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.