Electrical

CAUTION: Always vent the exhaust to the outside when performing this test.

Note: This procedure will diagnose only cooling systems that may not be reaching normal operating temperature. It will not diagnose a water thermostat that causes an engine overheat condition.

Note: Disconnecting the powertrain control module to attach a breakout box or an EEC IV monitor will erase the adaptive learning from memory and may "hide" a drive concern temporarily until the adaptive learning is relearned.

Note: This procedure is most accurate if performed indoors at less than 100°F (38°C) ambient temperature. This test may be performed with or without the hood open and with the engine warm or cold.

1. Check the coolant level in the radiator and radiator coolant recovery reservoir.
2. With the ignition switch in the OFF position, proceed as follows:
1. Remove the Engine Coolant Temperature (ECT) sensor harness connector.
2. Attach Rotunda Service Coolant Temperature Monitor Harness as a jumper between the PCM and the ECT.
3. Attach Rotunda 73 Digital Multimeter to the thermostat monitor harness. Voltage values (0-5 vdc) may now be monitored while the sensor retains its connection to the wiring harness.

Note: A Rotunda New Generation Star Tester (NGS) or the Rotunda Service Bay Diagnostic System (SBDS) may be used to monitor the ECT on vehicles equipped with Data Communications Link (DCL). The SBDS sequence to use for the screen is "tool box electronic engine control and DCL item".

3. Vehicles equipped with electric engine cooling fan(s) must have a cooling fan running during this test (high or low speed may be used). Two methods may be used to turn the fan(s) on:
1. Disconnect the A/C compressor clutch power supply and turn the climate control to A/C ON.
2. Disconnect the power supply to the cooling fan and supply 12 volts direct to the fan connector from the battery.

Note: A ground may be required for some applications.

4. Place transmission in PARK. or NEUTRAL.

Note: Running this test with the vehicle in gear or with the A/C compressor clutch engaged (running) will cause improper diagnosis.

5. Start the engine and allow to idle throughout this test:
1. Allow engine to run for 2 minutes, then record ECT voltage.
2. From now on, record ECT voltage every 60 seconds.
3. When the ECT voltage trend changes direction or changes only slightly (0.03 volts or less) from the previous reading, record this as the thermostat opening voltage.

Voltages And Corresponding Temperatures:

4. Use the Voltage and Corresponding Temperature Chart shown to obtain actual coolant temperatures.

6. If the opening voltage is GREATER than 0.75 volts (less than 180°F (82°C), replace the water thermostat.
7. If the thermostat opening voltage is LESS than 0.75 volts (greater than 180°F (82°C), the water thermostat is good and should NOT be replaced.