RACE 1T0737 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the Electronic Control Module (ECM). Also, use this procedure if any one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
CDL Code and Description Conditions which Generate this Code System Response
168-0 Electrical System Voltage : High The battery supply voltage is greater than 32 VDC for 2 seconds.
The ECM has been powered for 3 seconds.
The engine is not being cranked. The code is logged.
168-1 Electrical System Voltage : Low The battery supply voltage is less than 9 VDC for 2 seconds.
The ECM has been powered for 3 seconds.
The engine is not being cranked.
168-2 Electrical System Voltage : Erratic, Intermittent, or Incorrect The engine is running. The battery voltage falls below 9 VDC for one second. The voltage returns above 9 VDC.
or
Three voltage readings in the last 7 seconds were below 9 VDC.
1834-2 Ignition Keyswitch loss of signal The ECM detects at least three changes to the state of the signal that is for the keyswitch in the last one second. The code is logged.
Illustration 1 g02783177
Schematic for the electrical power supply (primary ECM) if equipped with A4 ECM
Illustration 2 g06328422
Schematic for the electrical power supply (primary ECM) if equipped with A5 ECM
Illustration 3 g02783178
Schematic for the electrical power supply (secondary ECM) if equipped with A4 ECM
Illustration 4 g06328429
Schematic for the electrical power supply (secondary ECM) if equipped with A5 ECM
Table 2
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring
A. Turn the battery disconnect switch to OFF.
B. Thoroughly inspect the electrical connectors and relays. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the proper procedure for inspecting system wiring.
C. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
D. Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
E. Check the harness and the wiring for abrasion and for pinch points.
Note: The next steps are for the A4 ECM only.
F. Check each of the fuses at the low current power distribution panel that are associated with the circuit. At the high current power distribution panel, ensure that the main circuit breaker has not been thrown.
Note: Replace any fuses that are blown. If necessary, reset the main circuit breaker.
Connectors
Results: The harness and wiring are OK.
Proceed to Test Step 2
Results: There is a problem in the connectors and/or wiring.
Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all the seals are properly in place and ensure that the connectors are coupled.
Verify that the repair eliminates the problem.
2. Check for Power to the Low Current Power Distribution Panel (A4 ECM Only)
A. Check the breakers for the primary and secondary ECM, primary and secondary keyswitch, and auxiliary circuits. Ensure that none of the circuit breakers are tripped. Correct any problem that is discovered.
B. Check the main circuit breaker at the high current power distribution panel. Ensure