The diagnostic condition is typically engine coolant temperature circuit failed low.
Short to Ground Check
Check as follows:
1. Disconnect the ECT Sensor.
2. Disconnect the 120–pin MCM connector.
3. Measure the resistance across pins 1 and 2 of the ECT Sensor harness connector.
See Figure 29-1.
[a] If resistance is greater than 5 Ω, go to step 4.
[b] If resistance is less than 5 Ω, repair short to ground between pins 55 and 110 of the 120-pin MCM connector. Refer to section 188.8.131.52.
4. Measure the resistance between pin 2 of the ECT Sensor harness connector and ground.
[a] If resistance is greater than 5 Ω, repeat steps 3 through 4. If the results are the same,
call the Detroit Diesel Customer Support Center (313–592–5800).
[b] If resistance is less than 5 Ω, repair the short circuit between pin 2 of the ECT Sensor
harness connector and ground. Refer to section 184.108.40.206.
Verify repairs as follows:
1. Turn ignition OFF.
2. Reconnect any electrical connections that were disconnected to perform the diagnosis.
3. Clear codes with DDDL 7.0 or latest version.
4. Start and bring engine up to operating temperature (over 140°F/60°C).
5. Verify operation is satisfactory and no warning lamps illuminate. If warning lamps illuminate, troubleshoot the codes. If assistance is required, call the Detroit Diesel Customer Support Center at 313–592–5800.