FILTER 3I0508 - Caterpillar

There are two different types of cylinder firing signals. The number one cylinder firing signal indicates that the Electronic Control Module (ECM) is commanding the spark plug in the number one cylinder to fire. The all cylinders firing signal indicates that the ECM is commanding the spark plug in each cylinder to fire. Each signal is developed on a wire that connects the ECM to the Integrated Sensing Module (ISM).The 725-8 diagnostic code is caused if the number one cylinder firing signal and the all cylinders firing signal are connected to the opposite terminals somewhere in the circuit. A -2, -3, and -4 diagnostic code is probably caused by a problem with a harness connector or with the wiring. The next likely cause is a faulty electronic component.Logged codes provide a historical record. Before you begin this procedure, use the Cat® Electronic Technician (ET) to create a Product Status Report and save prior to clearing any logged or active diagnostic codes. Save report to file for future reference.This troubleshooting procedure may generate additional codes. Keep your mind on correcting the cause of the original code. Clear the codes after the problem is resolved.
Illustration 1 g03811626
Table 2
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring
A. Turn the main disconnect switch to the OFF position.
B. Thoroughly inspect the connectors. Refer to Troubleshooting, "Electrical Connectors-Inspect" for additional information.
C. Perform a 45 N (10 lb) pull test on the connector wires.
D. Check the harness for abrasions and pinch points.
Connectors and Wiring
Result: The connectors and wiring appear to be OK.
Proceed to Test Step 2.
Result: There is a problem with the connectors and/or wiring.
Repair: Repair or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled.
If the problem is not resolved, proceed to Test Step 2.
2. Check for Codes
A. To prevent the engine from starting, shut the main gas supply OFF.
B. Connect Cat® Electronic Technician (ET) to the service tool connector.
C. Crank the engine for ten seconds.
D. Look for active codes.
Codes
Result: There are no active or logged codes. The cylinder firing signals are operating correctly at this time.
Result: A -2 code is active.
Proceed to Test Step 5.
Result: A -3 code is active.
Proceed to Test Step 3.
Result: A -4 code is active.
Proceed to Test Step 4.
Result: A -8 code is active.
Repair: A cylinder firing signal is abnormal. The Electronic Control Module (ECM) detects that the signal wires for the #1 cylinder and the signal wire for all cylinders have been swapped. Check for an incorrect cylinder firing signal wire connection at the ECM and Integrated Sensing Module (ISM).
Verify that the repair eliminated the problem.
3. Check Wiring Harness for a Short Circuit to a Positive Voltage Source
A. Turn the main disconnect switch to the ON position with the engine OFF.
B. Measure voltage on the affected cylinder firing signal wire at the ECM or ISM.
Connectors and Wiring
Result: Voltage was found on the affected cylinder firing signal wire with engine speed not present.
Repair: A