RELAY 9W0266 - Caterpillar

When a filter has been replaced and the bypass switch continues to indicate that a problem exists, further troubleshooting is necessary to isolate the problem. Refer to the Systems Operations, "Switches" section for additional information on the individual switches.The possible causes of these failures are listed below:
The signal circuit in the machine harness is open.
The switch has failed.
The ECM has failed.Test Step 1. CHECK FOR AN OPEN IN THE HARNESS
Locate the switch that corresponds to the alert indicator that is located on the main display module. (If necessary, use the Electrical System Schematic to assist in locating the switch.)
Disconnect the signal wire from the switch.
Place a jumper wire from the signal wire to the ground wire. Expected Result:The alert indicator is no longer active on the main display module.Results:
OK - The alert indicator is no longer active on the main display module.Repair: The switch has failed. Check or replace the switch. STOP
NOT OK - The alert indicator remains on the main display module. The machine harness is open or the ECM has failed. Proceed to test step 2.Test Step 2. CHECK THE VOLTAGE OF THE ECM.
Remove the jumper that was used in the previous test step.
The signal wire remains disconnected.
Measure the pull-up voltage from the signal wire to the ground wire with a digital multimeter. Expected Result:The voltage is 5 0.5 volts. Results:
OK - The voltage is 5 0.5 volts. Repair: The voltage is correct. The ECM has failed. It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the fault is not found, replace the ECM. See Testing and Adjusting, "Module - Replace".STOP
NOT OK - The voltage is NOT 5 0.5 volts. Proceed to test step 3.Test Step 3. CHECK THE SIGNAL CIRCUIT OF THE HARNESS.
Turn the key start switch and the disconnect switch to the OFF position.
Use the Electrical System Schematic to trace the signal wire from the switch back to the ECM.
Determine the signal contact (connector contact) of the machine harness at the ECM.
Disconnect the machine harness connector(s) from the ECM.
At the machine harness connector for the ECM, measure the resistance between the signal contact and contact 2 of the switch. Expected Result:The resistance is less than 5 ohms. Results:
OK - The resistance is less than 5 ohms. The signal circuit of the harness is correct. Proceed to test step 4.
NOT OK - The resistance is greater than 5.0 ohms. Repair: The signal circuit of the harness is not correct. Repair the machine harness or replace the machine harness.STOPTest Step 4. CHECK THE GROUND CIRCUIT OF THE HARNESS.
The key start switch and the disconnect switch remain in the OFF position.
The machine harness connector(s) remain disconnected from the ECM.
Use the Electrical System Schematic to trace the ground for the switch.
At the switch, measure the resistance between the ground wire and frame ground. Expected Result:The resistance is less than 5 ohms. Results:
OK - The resistance is less than 5 ohms.Repair: The machine harness is not the cause