DTC 15

DTC 14 Circuit Diagram:

DTC 15 Diagnostic Chart Low Temperature Indicated In Coolant Temperature Sensor Circuit:

CIRCUIT DESCRIPTION:

The Coolant Temperature Sensor (ECT) uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on GRY/BLK wire to the sensor. When the engine is cold, the sensor (thermistor) resistance is high, therefore, the ECM will sense 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 A11. Coolant temperature is one of the inputs used by the ECM to control the following:

^ Electronic Spark Timing (EST).
^ Fuel delivery.
^ Idle Air Control (IAC).

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

1. Checks to see if code was set as result of hard failure or intermittent condition. Code 15 will set if signal Voltage indicates a coolant temperature below -39°C (-38°F) and the engine has been running for 120 seconds.

2. This test 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 a faulty ECM.

DIAGNOSTIC AIDS:

A "Scan" tool reads engine temperature in degrees Centigrade and Fahrenheit. After the engine is started, the temperature should rise steadily to about 194°F (90°C), then stabilize when the thermostat opens. If the engine has been allowed to cool to an ambient temperature (overnight), coolant temperature and Manifold Air Temperature (MAT) may be checked with a Scan tool and should read close to each other. A Code 15 will result if GRY or GRY/BLK wire are open. If Code 15 is intermittent,
Intermittant Check Procedure