CUTTING EDGE 9W9794 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engine Electronic Control Module (ECM). Also use this procedure if any one of the diagnostic codes in Table 1 is active or easily repeated.Note: Some of the following codes may not be applicable for certain applications.
Table 1
Diagnostic Trouble Codes    
J1939 Code    CDL Code    Code Description    Comments    
168-2     168-2     Electrical System Voltage : Erratic, Intermittent, or Incorrect     The engine is running. The battery voltage falls below 6 VDC and the voltage returns above 9 VDC for three voltage readings in the last 7 seconds.    
168-3     168-3     Electrical System Voltage : Voltage Above Normal     The ECM detects voltage that is above the acceptable value.    
168-4     168-4     Electrical System Voltage : Voltage Below Normal     The ECM detects voltage that is below the acceptable value.    
158-2     1834-2     Ignition Key Switch loss of signal     The ECM detects an erratic signal from the keyswitch because the keyswitch was cycled at least three times in the last second    The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).
Illustration 1 g02154189
Illustration 2 g02361008
Terminal locations at the P1 ECM connector that are for electrical power (P1-48) +Battery (if applicable) (P1-52) +Battery (if applicable) (P1-53) +Battery (if applicable) (P1-55) +Battery (if applicable) (P1-57) +Battery (if applicable) (P1-61) -Battery (if applicable) (P1-63) -Battery (if applicable) (P1-65) -Battery (if applicable) (P1-67) -Battery (if applicable) (P1-69) -Battery (if applicable) (P1-70) Keyswitch
Table 2
Troubleshooting Test Steps    Values    Results    
1. Determine the Diagnostic Code
A. Establish communication between the Cat ET and the ECM . Refer to Troubleshooting, "Electronic Service Tools", if necessary.
B. Start the engine. Run the engine until the engine is at normal operating temperature.
C. Download the "Warranty Report" from the engine ECM before performing any troubleshooting or clearing diagnostic trouble codes. Look for these codes:
168-2
168-3
168-4
1834-2
   
Diagnostic Codes    
Result: A 168-2 or a 1834-2 diagnostic code is active.
Proceed to Test Step 2.
Result: A 168-3 diagnostic code is active.
Proceed to Test Step 3.
Result: A 168-4 diagnostic code is active.
Proceed to Test Step 4.
   
2. Inspect the Electrical Connectors and the Wiring For the Charging Circuit
A. Turn the keyswitch to the OFF position.
B. Check the harness connections at the battery and at the alternator.
C. Check the harness between the battery and the alternator.
   
Connectors and Wiring    
Result: OK - The harness and connectors appear to be OK.
Repair: There is a problem with the charging system. Refer