MBE 4000 DDEC VI Troubleshooting – Section 25.3 SPN 91/FMI 4

Section 25.3
SPN 91/FMI 4

The typical diagnosis for this fault is circuit failed low.‪

Section 25.3.1
Low Voltage Check

Perform the following steps to troubleshoot low voltage.‪

1. Disconnect the Accelerator Pedal (AP) connector.
2. Disconnect the CPC #1 connector.
3. Measure the voltage between pins B and C of the AP connector.
   1. If the voltage is between 4.5 and 5.5 volts, go to step 5 See Figure "Accelerator Pedal Assembly Installation" .
   2. If the voltage is less than 4.5 volts, go to step 4 .
   

   Figure 1. Accelerator Pedal Assembly Installation

4. Measure the voltage between pin C of the AP harness connector and ground.
   1. If the voltage is between 4.5 and 5.5 volts, repair the open circuit between pin B of the AP harness connector and pin 4 of the CPC #1 connector. Refer to "25.3.1.1 Verify Repairs" .
   2. If the voltage is less than 4.5, repair the open circuit between pin C of the AP harness connector and pin 8 of the CPC #1 connector. Refer to "25.3.1.1 Verify Repairs" .
5. Turn OFF the ignition.
6. Disconnect the CPC #1 connector.
7. Measure the resistance between pins B and pin C of the AP connector.
   1. If the resistance is less than 5 Ω, repair the short between wires 8 and 4 of the CPC #1 connector. Refer to "25.3.1.1 Verify Repairs" .
   2. If the resistance is greater than 5 Ω, go to the next step.
8. Measure the resistance between pin A and B of the AP connector.
   1. If the resistance is less than 5 Ω, repair the short between wires 7 and 4 of the CPC #1 connector. Refer to "25.3.1.1 Verify Repairs" .
   2. If the resistance is greater than 5 Ω, go to the next step.
9. Measure the resistance between pin C of the AP connector and ground.
   1. If the resistance is less than 5 Ω, repair the short circuit between pin C of the AP connector and ground. Refer to "25.3.1.1 Verify Repairs" .
   2. If the resistance is greater than 5 Ω, go to the next step.
10. Measure the resistance between pin A of the AP connector and ground.
    1. If the resistance is less than 5 Ω, repair the short circuit between pin A of the AP connector and ground. Refer to "25.3.1.1 Verify Repairs" .
    2. If the resistance is greater than 5 Ω, replace the Accelerator Pedal. Refer to "25.3.1.1 Verify Repairs" .

Section 25.3.1.1
Verify Repairs

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.