ENGINE ARRANGEMENT 8N3905 - Caterpillar

Illustration 1 g00530708
Schematic For The Caterpillar Data LinkNote: Ensure that the "SERV CODE" indicator is ON.This diagnostic code is recorded when the Main Display Module does not receive expected information. For example, the engine speed is not received from the Engine Electronic Control Module (engine ECM) through the Cat Data Link. As a result of this diagnostic condition, the display area depends on the Cat Data Link for information that indicates abnormal values. The following items are possible causes of the readouts. The causes are listed in order of probability.
There is a poor electrical connection at the engine harness connector.
The Cat Data Link circuit in the engine harness is shorted to ground.
The Cat Data Link circuit in the engine harness is shorted to +battery.
The Cat Data Link circuit in the engine harness is open.
Another electronic module (Secondary ECM, DeNOx Controller, CCM, PRCM and other modules) that also uses the Cat Data Link is having a problem.Note: If the Main Display Module was recently replaced, see Testing And Adjusting, "Main Display Module Initialization - Adjust" for more information.
Check the other Electronic Modules for a similar diagnostic code.
If a similar diagnostic code is found, use the procedures for that electronic module to troubleshoot the diagnostic code.
If no similar diagnostic code is found, proceed to Step 2.
Inspect The Harness Connectors.
Turn the "ECS" switch to the OFF/RESET position.
Inspect the engine harness connectors that are related to the Cat Data Link. Make sure that the connections are clean and tight.
If necessary, repair the engine harness or replace the engine harness. Otherwise, proceed to Step 3.
Check For A Short To Ground.
The "ECS" switch remains in the OFF/RESET position.
Disconnect the engine harness from all electronic modules that use the Cat Data Link.
At the engine harness connector for the Main Display Module, measure the resistance between the battery ground (contact 2) and the Cat Data Link circuits (contact 5 and contact 14).Expected Result: The harness circuit resistance should be greater than 5000 ohms.Results:
OK - The harness circuit resistance is correct. Proceed to Step 5.
Not OK - The harness circuit resistance is less than 5000 ohms. The engine harness has a problem. There is a short between battery ground and the circuit for the Cat Data Link in the engine harness. Repair the engine harness or replace the