FAN OPERATIONAL CONCERN (VARIABLE SPEED TYPE)
10.9 FAN OPERATIONAL CONCERN (VARIABLE SPEED TYPE)
The DDEC system via a PWM (Pulsewidth Modulation) signal will go to a high voltage (7-8 volts
on a 12-volt system) on a cold engine for a low speed, and to a low voltage (0.8 - 1.0 volts on
a 12-volt system) for a high speed.
Fan speed is ramped up as temperatures increase, as listed in Table 10-10. Calibrations can
vary. The table is provided only as a guide.
up to 197
F and above
Fan Speed vs Temperature
Verify Correct DDEC Configuration
Perform the following steps to verify the configuration:
1. Turn ignition ON.
2. Plug in DDR.
3. Select "View Calibration" (ECM Ins/Outs).
4. Review PWM functions to determine correct pin assignment for PWM fan.
[a] If the cavity is assigned to PWM Fan, refer to section 10.9.2.
[b] If the cavity is not programmed, reprogram the ECM and refer to section 10.9.7.
Check for Signal
Perform the following steps to check for signal:
1. Start and run the engine at idle.
2. Plug in DDR.
3. Review engine data list and watch the pulsewidth modulation number x wire = # of fan
assignment (normally PWM#4).
4. Verify coolant, oil and air temperatures are cooler, less than 150
F. Verify the air
conditioning input is grounded (On).
[a] If the PWM value is 80 to 90% and the fan is at Low Speed, refer to section 10.9.3.
[b] If the PWM value is 80 to 90% and the fan is at High Speed, refer to section 10.9.4.
All information subject to change without notice.
6SE497 9709 Copyright © 1997 DETROIT DIESEL CORPORATION