MBE 900 DDEC VI Troubleshooting – Section 123.1 SPN 3661/FMI 6

Section 123.1
SPN 3661/FMI 6

This diagnosis is typically the Electronic Unit Pump Cylinder #3, Circuit Shorted to Battery.‪

1. Turn the ignition OFF.
2. Disconnect the MCM 120 pin connector.
3. Using the J-48475 breakout box and J-48583 overlay connect the MCM side of the harness ONLY.
4. Turn the ignition ON.
5. Measure the voltage between pin 12 of the J-48475 breakout box and ground.
   1. If voltage is greater than 0.5v, contact the CSC for MCM replacement authorization.
      

      Figure 1. Electronic Unit Pump #3

   2. If no voltage is present, repair short to power between pin 12 of the MCM 120 pin connector and the #3 Electronic Unit Pump. See Figure "Electronic Unit Pump #3"