C7 and C9 Industrial Engines Troubleshooting – Electrical Power Supply – Test

This procedure covers the following diagnostic codes:


  • 168-00 System Voltage High
  • 168-01 System Voltage Low
  • 168-02 System Voltage intermittent/erratic

This procedure tests whether proper voltage is being supplied to the Electronic Control Module (ECM).

Unswitched battery voltage is supplied through the customer connector to the ECM at P1-48, P1-52, P1-53, and P1-55. The negative battery is supplied to the ECM at P1-61, P1-63, P1-65, and P1-69. The ECM receives the input from the keyswitch at P1-70 when the keyswitch is in the ON position or the START position. When the ECM detects battery voltage at this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down.

The cause of an intermittent power supply to the ECM can occur on either the positive side or the negative side of the battery circuit. Both sides are routed from the ECM to the battery. The three connections for the unswitched +Battery should be routed through a dedicated protective device (circuit breaker).

The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with the electronic service tool.

Illustration 1 g01302403
Schematic diagram for the electrical power supply

Illustration 2 g01120079
Left side view

(1) P61 customer connector

(2) J1/P1 ECM connectors

Illustration 3 g01302468
P1 terminals that are associated with the electrical power supply

(P1-44) Shutdown

(P1-48) +Battery

(P1-52) +Battery

(P1-53) +Battery

(P1-55) +Battery

(P1-61) −Battery

(P1-63) −Battery

(P1-65) −Battery

(P1-69) −Battery

(P1-70) Keyswitch

Illustration 4 g01216338
J61 and P61 terminals that are associated with the electrical power supply

(1) +Battery

(26) Keyswitch

(27) Shutdown

(31) +Battery

(32) +Battery

Table 1
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring

A. Check all circuit breakers.

B. Check the battery.

C. Turn the keyswitch to the OFF position.

D. Thoroughly inspect connectors (1) and (2). Inspect the connections for the battery and the connections to the keyswitch. Refer to Troubleshooting, “Electrical Connectors – Inspect”, for details.

E. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the electrical power supply.

F. Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, “Electrical Connectors – Inspect”, for the correct torque values.

G. Check the harness and wiring for abrasions and for pinch points from the battery to the ECM. Also, check the harness and wiring for abrasions and for pinch points from the keyswitch to the ECM.

Electrical Connectors and Wiring Results: The connectors and wiring are OK. Proceed to Test Step 2.

Results: There is a problem with the connectors or wiring.

Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled.


2. Check the Battery Voltage at the ECM

A. Disconnect the J1/P1 ECM connector.

B. Turn the keyswitch to the ON position.

C. Measure the voltage between P1-52 (Unswitched Positive Battery) and P1-63 (Negative Battery).

D. Measure the voltage between P1-48 (Unswitched Positive Battery) and P1-61 (Negative Battery).

E. Measure the voltage between P1-53 (Unswitched Positive Battery) and P1-65 (Negative Battery).

F. Measure the voltage between P1-55 (Unswitched Positive Battery) and P1-69 (Negative Battery).

G. Measure the voltage between P1-70 (Keyswitch) and P1-63 (Negative Battery).

The measured voltage is between 11.0 VDC and 13.5 VDC for a 12 V system and between 22.0 VDC and 27.0 VDC for a 24 V system. Results: The ECM is receiving the correct voltage.

Repair: If an intermittent condition is suspected, refer to Troubleshooting, “Electrical Connectors – Inspect”.


Results: Battery voltage is out of range Proceed to Test Step 3.

Results: Keyswitch voltage out of range

Repair: Check the circuit protection for the circuit and for the wiring. Trace the wiring for the keyswitch from the ECM through the keyswitch circuit to the batteries. Find the problem and repair the problem. Verify that the repairs eliminate the problem.

3. Check the Batteries

A. Measure the no-load battery voltage at the battery posts.

B. Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to Special Instruction, SEHS9249, “Use of 4C-4911 Battery Load Tester for 6, 8 and 12 V Lead Acid Batteries” and Special Instruction, SEHS7633, “Battery Test Procedure”.

Minimum specification for a 12V or 24V system Results: The batteries are OK.

Repair: Check the wiring between the batteries and the ECM for shorts. Check the connectors between the batteries and the ECM for moisture and/or corrosion. Repair the wiring and/or the connectors. Verify that the repair eliminates the problem.


Results: The battery voltage is low or the battery did not pass the load test.

Repair: Recharge or replace the faulty batteries. Verify that the repair eliminates the problem.



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