DDEC III/IV Single ECM Troubleshooting – Section 10.9 Fan Operational Concern (Variable Speed Type)

Section 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 "Fan Speed vs Temperature" . Calibrations can vary. The table is provided only as a guide. ‪

Coolant Temperature ‪	Speed ‪
up to 197°F‪	Low speed‪
about 203°F‪	Medium speed‪
208°F and above‪	High speed‪

Section 10.9.1
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.
   1. If the cavity is assigned to PWM Fan, refer to "10.9.2 Check for Signal" .
   2. If the cavity is not programmed, reprogram the ECM and refer to "10.9.7 Verify Repairs" .

Section 10.9.2
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 pulse width 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).
   1. If the PWM value is 80 to 90% and the fan is at Low Speed, refer to "10.9.3 Check Signal Engine Hot" .
   2. If the PWM value is 80 to 90% and the fan is at High Speed, refer to "10.9.4 Check for Open" .

Section 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).
   1. 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 circuit. Refer to "10.9.7 Verify Repairs" .
   2. If PWM % decreases as the temperature increases, but the fan speed stays low, refer to "10.9.5 Check for Short" .

Section 10.9.4
Check for Open

Perform the following steps to check for an open circuit:‪

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 (-).
   1. If the measured resistance is greater than 1,000 Ω, the wire is open. Repair the break and refer to "10.9.7 Verify Repairs" .
   2. If the measured resistance is less than 1,000 Ω, the valve or wiring (voltage supply) to the valve is defective. Replace.

Section 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.).
   1. If the measured resistance is greater than 1,000 Ω, refer to "10.9.6 Check Connectors" .
   2. If the measured resistance is less than 1,000 Ω at any time, the wiring is shorting. Replace the wire and refer to "10.9.7 Verify Repairs" .

Section 10.9.6
Check Connectors

Perform the following steps to check the connectors:‪

1. Check for damaged, bent or corroded connectors, pins, and terminals.
   1. If the connectors, pins, and terminals are not damaged, contact the OEM or fan valve supplier for instructions on further troubleshooting. If the ECM and wiring to the component appear to be okay, the problems could be with the control valve or battery and wiring.
   2. If the connectors, pins or terminals are damaged, repair or replace them and refer to "10.9.7 Verify Repairs" .

Section 10.9.7
Verify Repairs

Perform the following steps to verify repairs: ‪

1. Connect all removed connectors, etc.
2. Start and run the engine from cold to hot, while watching the fan speed operation.
   1. If the operation is normal, troubleshooting is complete.
   2. If the operation is not normal, all system diagnostics are complete. Review this section to find the error. Refer to "10.9.1 Verify Correct DDEC Configuration" .