With PFI

Code 15 Chart:

Code 15 Wiring Diagram:

CIRCUIT DESCRIPTION:

The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the Electronic Control Module (ECM). The ECM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage. 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 the ECM terminal "YE16".

Coolant temperature is one of the inputs used to control:

^ Fuel Delivery
^ Electronic Spark Timing (EST)
^ Cooling Fan
^ Torque Converter Clutch (TCC)
^ Idle Air Control (IAC)


NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.

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

1. Checks to see if code was set as a result of hard failure or intermittant problem.
Code 15 will set if:

^ Engine has been running for more than 50 seconds.
^ Signal voltage indicates indicates a coolant temperature below -30~C (-22~F).

2. This simulates conditions for a code 14, If the ECM recognizes the grounded circuit (low voltage) and displays a high temperature, the ECM and wiring are OK.

3. This test will determine if there is a wiring problem or faulty ECM. If CKT 452 is open, there may also be a code 21 stored.


DIAGNOSTIC AIDS:

^ A "Scan" tool reads engine temperature in degrees centigrade. After engine is started the temperature should rise steadily to about 90~C (194~F) then stabilize when thermostat opens.

^ If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperature may be checked with a "Scan Tool" and should read close to each other.

^ When a code 15 is set, the ECM will turn "ON" the engine cooling fan.

^ A code 15 will result if CKT 410 or 452 are open.

^ If code 15 is intermittant, Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.