Section 32.2
SPN 168/FMI 1

This diagnosis is typically battery voltage low.‪

Section 32.2.1
Alternator and Battery Check

Check as follows:‪

1. Check the condition of the alternator drive belt and replace, if required.
   1. If fault is no longer active, refer to "32.2.2.1 Verify Repairs" .
   2. If fault is still active, go to step 2 .
2. Check for loose alternator mounting and retighten or repair, as required.
   1. If fault is no longer active, refer to "32.2.2.1 Verify Repairs" .
   2. If fault is still active, go to step 3 .
3. Check for proper alternator operation and repair or replace, as required.
   1. If fault is no longer active, erase fault code memory.
   2. If fault is still active, go to step 4 .
4. Check the condition of the battery (does it hold the charge?) and replace, if required.
   1. If fault is no longer active, refer to "32.2.2.1 Verify Repairs" .
   2. If fault is still active, refer to "32.2.2 Measure the Resistance" .

Section 32.2.2
Measure the Resistance

Measure the resistance as follows:‪

1. Measure the resistance of the individual wires in the ground circuit (MCM 21/5, 21/6, 21/8, 21/9 and CPC 2/2). See Figure "Power Wiring" .
   1. If resistance is greater than 0.5 Ω in any wire, repair or replace the wire and connector.Refer to "32.2.2.1 Verify Repairs" .
   2. If resistance is less than 0.5 Ω in all wires, go to step 2 .
   

   Figure 1. Power Wiring

2. Measure the resistance of the individual wires in the power circuit (MCM 21/11, 21/12, 21/14, 21/15 and CPC 2/1) with the engine running and battery voltage greater than 12.5 V. See Figure "Power Wiring" .
   1. If resistance is greater than 0.5 Ω in any wire, repair or replace the power circuit wires and connector. Refer to "32.2.2.1 Verify Repairs" .
   2. If resistance is less than 0.5 Ω in any wire, go to step 3 .
3. Measure the current drop of the individual wires in the ground circuit (MCM 21/5, 21/6, 21/8, 21/9 and CPC 2/2). See Figure "Power Wiring" .
   1. If the current drop is more than 0.2 volts in any wire, repair or replace the ground circuit wires and connector. Refer to "32.2.2.1 Verify Repairs" .
   2. If the current drop is less than 0.2 volts in any wire, go to step 4 .
4. Measure the current drop of the individual wires in the power circuit (MCM 21/11, 21/12, 21/14, 21/15 and CPC 2/1).See Figure "Power Wiring"
   1. If the current drop is more than 0.2 volts in any wire, repair or replace the power circuit wires and connector. Refer to "32.2.2.1 Verify Repairs" .
   2. If the current drop is more than 0.2 volts in any wire, refer to "32.2.2.1 Verify Repairs" .

Section 32.2.2.1
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.