DDEC TROUBLESHOOTING
10.9.3
Check Signal Engine Hot
Perform the following steps to check the signal status:
1. Start engine and warm up. Road test (until coolant temp is about 200
F).
2. View DDR data list display, Coolant Temp/PWM # (normally #4).
[a] If PWM % decreases as the temperature increases, all checks appear normal. If this is
an intermittent high speed operation, check A/C Freon pressure switch or wiring for
an intermittent open. Refer to section 10.9.7.
[b] If PWM % decreases as the temperature increases, but the fan speed stays low,
refer to section 10.9.5.
10.9.4
Check for Open
Perform the following steps to check for an open:
1. Turn ignition OFF.
2. Unplug PWM wire at the fan control valve.
3. Install a jumper between the PWM wire and the battery (-).
4. Unplug the engine harness connector.
5. Measure resistance between the PWM cavity and the battery (-).
[a] If the measured resistance is greater than 1,000 , the wire is open. Repair the
open and refer to section 10.9.7.
[b] If the measured resistance is less than 1,000 , the valve or wiring (voltage supply) to
the valve is defective. Replace.
10.9.5
Check for Short
Perform the following steps to check for a short:
1. Turn ignition OFF.
2. Unplug the engine harness connector.
3. Measure resistance between the PWM cavity and several ground sources (battery, chassis,
etc.).
[a] If the measured resistance is greater than 1,000 , refer to section 10.9.6.
[b] If the measured resistance is less than 1,000
at any time, the wiring is shorting.
Replace the wire and refer to section 10.9.7.
10.9.6
Check Connectors
Perform the following steps to check the connectors:
1. Check for damaged, bent or corroded connectors, pins, and terminals.
All information subject to change without notice.
6SE497 9709 Copyright © 1997 DETROIT DIESEL CORPORATION
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