ROD AS 9T2456 - Caterpillar

Illustration 1 g03476470
Schematic of the Backup Alarm
When the shift lever is in the REVERSE position, a signal is sent to the Transmission Electronic Control Module (ECM). The Transmission ECM switches the backup alarm relay coil to frame ground. When the backup alarm relay is energized, +battery is applied to the backup alarm.If the backup alarm is always off, check these items:
The fuse for the relay is open.
The backup alarm has failed.
The machine harness has failed.
The machine harness is shorted to frame ground.
The backup alarm relay has failed.
The ECM has failed. This situation is unlikely.Note: The diagram above is simplified schematic of the relay connections for the Backup Alarm. The schematic is electrically correct. However, not all of the possible harness connectors are shown. For the complete schematic information reference Electrical Schematic , UENR3118, "950 GC Wheel Loaders".Troubleshooting Procedure
Note: Prior to beginning this procedure, inspect the harness connectors that are involved in the circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure and in good condition. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure.Note: The voltage to operate the Backup Alarm is supplied from location A16 on the fuse panel (15A). If the Backup Alarm is not functioning, the technician must confirm that continuity exists across the fuse.
Table 1
Troubleshooting Test Steps Values Results
1. Check The Relay Circuit
A. Turn the key start switch and the battery disconnect switch to the OFF position.
B. Remove the backup alarm relay.
C. Turn the battery disconnect switch and the key start switch to the ON position.
The backup alarm is OFF. OK: The backup alarm is OFF.
Proceed to Test Step 2.
NOT OK: The backup alarm is ON.
Proceed to Test Step 4.
2. Check The Relay Contacts
A. Turn key start switch and disconnect switch OFF.
B. Disconnect harness connection at relay.
C. Check the resistance between contact 85 and contact 86 of the backup alarm relay.
The resistance is less than 1K Ω. OK: The resistance measurement is less than 1K Ω.
Proceed to Test Step 3.
NOT OK: The resistance is greater than 1K Ω
Repair: The relay for the Backup Alarm has failed, replace the relay.
STOP
3. Check The Return Circuit Of The Relay For An Open
A. Disconnect the machine harness J2 connector from the ECM.
B. Place a jumper from pin J2-2 to J2-8 at the J2 connector for the ECM.
C. At the harness connector for the backup alarm relay, measure the resistance between contact 85 (wire J814-BK(Black)) and contact 86 (wire A626-GN(Green))
The measured resistance is less than 5 Ω. OK: The measured resistance is less than 5 Ω.
Proceed to Test Step 4.
NOT OK: The resistance is greater than 5 Ω. The machine harness has failed.
Repair: Repair the machine harness or replace the machine harness.
4. Check The Backup Alarm
A. Remove the jumper from the previous Test Step.
B. At the connector for the backup alarm, measure the resistance between contact 1 (wire 321-BR(Brown)) and