Part 1 of 2

CODE 14 COOLANT TEMPERATURE SENSOR CIRCUIT

Code Chart 14A:

CTS Circuit:

CIRCUIT DESCRIPTION:

The Coolant Temperature Sensor (CTS) uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on GRAY 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 14A will set if signal Voltage indicates a coolant temperature above 135°C (275°F) for 3 seconds.

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

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 14A will result if GRAY wire is shorted to ground. If Code 14A is intermittent, Testing and Inspection