DTC 15

Coolant Temperature Sensor (CTS) Circuit Diagram:

CIRCUIT DESCRIPTION:
The coolant temperature sensor uses a thermistor to control the signal voltage to the PCM. The PCM applies a reference voltage on CKT 410 to the sensor and then monitors the voltage in the circuit. When the engine is cold the sensor (thermistor) resistance is high, therefore, the PCM will see high signal voltage. As the engine warms, the sensor resistance decreases, and the circuit voltage drops. At normal engine operating temperature (85°C to 95°C), the voltage will measure about 1.5 to 2.0 volts.

Code 15 will set if the following conditions exist.
^ Engine running for more than 20 seconds.
^ Voltage as measured at circuit 410 indicates temperature less than -39°C (-36°F).

TEST DESCRIPTION

Code 15 Diagnostic Chart:

Numbers below refer to circled numbers on the diagnostic chart.

1. Checks to see if sensor circuit is actually indicating conditions necessary to set a code 15.
2. This test checks the wiring and PCM by simulating conditions for a code 14 (high temp indicated). If the PCM recognizes the low signal voltage and the "SCAN" tool displays engine temperature 130°C (266°F) or greater, then the PCM and wiring are OK.
3. This test determines if the problem is an open circuit 410 or 808, or if the PCM is faulty. With circuit 410 grounded (either by jumpering to circuit 808 or by jumpering straight to ground), "SCAN" tool should display coolant temperature of 130°C (266°F) or more.

DIAGNOSTIC AIDS

^ A faulty connection or an open circuit 410 or 808 will result in a Code 15. Codes 15 and 21 stored at the same time may be the result an open ground circuit 808, which would also turn the temperature warning light "ON"

^ "Scan" tool displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C then stabilize when thermostat opens, An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation.

^ Intermittent Test
If connections and harness check OK, "Scan" coolant temperature while moving related connectors and wiring harness. If the failure is induced, the "coolant temperature" display will change. This may help to isolate the location of the malfunction.

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