SEAL 9T0556 - Caterpillar

Use this procedure under the following situation:The circuit for the diagnostic enable switch is suspected of incorrect operation.Diagnostic Enable SwitchThe diagnostic enable switch is used to prompt the Engine Control Module (ECM) to display diagnostic flash codes on the check engine lamp. For more information, refer to the "Flashing Out Diagnostic Flash Codes" section in Troubleshooting, "Check Engine Lamp Circuit - Test". The feature is disabled if the "Diagnostic Enable Switch" parameter is programmed to "None" (default). If the "Diagnostic Enable Switch" parameter is programmed to J1/P1:46, then the feature is available and the switch circuit should be wired to P1-46 at the ECM connector.
Illustration 1 g01256017
Schematic for the diagnostic enable switch
Test Step 1. Check the Status of the Diagnostic Enable Switch
Turn the keyswitch to the OFF position.
Connect Caterpillar Electronic Technician (ET) to the data link connector.
Turn the keyswitch to the ON position.
Monitor the status for the "Diagnostic Enable" while the diagnostic enable switch is toggled to the ON position and the OFF position. The correct status for the "Diagnostic Enable" is "On" when the switch is in the ON position. The correct status for the "Diagnostic Enable" is "Off" when the switch is in the OFF position.Note: If the status for the "Diagnostic Enable" indicates "Not Installed", then the "Diagnostic Enable" parameter has not been programmed.
Turn the keyswitch to the OFF position. Expected Result:Cat ET correctly displayed the status for the diagnostic enable switch.Results:
OK - Cat ET correctly displayed the status for the switch.Repair: The diagnostic enable switch appears to operating correctly at this time. There may be an intermittent electrical problem in the harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting intermittent electrical problems.STOP
Not OK - Cat ET is not reporting the correct status for the switch. The ECM is not reading the change in switch status. Proceed to Test Step 2.Test Step 2. Determine the Configuration of the Diagnostic Enable Switch
Determine if the diagnostic enable switch is wired directly to the ECM, or if the switch position is reported on the J1939 data link.
Verify that the "Diagnostic Enable" parameter is programmed to reflect the current wiring for the circuit. Expected Result:The diagnostic enable switch is wired directly to the ECM.Results:
OK - The diagnostic enable switch is wired directly to the ECM. Proceed to Test Step 3.
Not OK - The diagnostic enable switch is wired directly to the ECM.Repair: The switch position is reported to the ECM via the J1939 data link. Verify that the "Diagnostic Enable" parameter is programmed to "J1939 - Body Controller", "J1939 - Cab Controller", or "J1939 - Instrument Cluster".Refer to Troubleshooting, "Powertrain Data Link Circuit - Test".STOPTest Step 3. Check the Electrical Connectors and the Wiring
Illustration 2 g01186024
Location of the J1/P1 ECM connectors (typical left side engine view)
Thoroughly inspect the J1/P1 ECM connector and the firewall bulkhead connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 3 g01259180
Terminal locations at the ECM connector for the diagnostic