DTC 15

Code 15 Diagnostic Chart:

TPS, CTS, & IAT Sensors (Circuit Diagram):

CIRCUIT DESCRIPTION:
The coolant temperature sensor uses a thermistor to control the signal voltage to the PCM. The PCM applies a voltage on CKT 410 to the sensor. 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 becomes less, and the 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 2 seconds.
^ Voltage as measured at circuit 410 indicates temperature less than -39°C (-36°F).

TEST DESCRIPTION
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. If the PCM recognizes the low signal voltage (high temperature indicated), and the "SCAN" tool displays engine temperature 130°C (266°F) or greater, then the PCM and wiring are OK.

DIAGNOSTIC AIDS
^ "Scan" tool displays engine temperature in °C or °F. After engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize as thermostat opens. An intermittent may be caused by a poor connection, 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 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.