Use this procedure under the following conditions:
This procedure tests whether proper voltage is supplied by the wiring. Use this procedure if the diagnostic code is logged or active.
- 168-0 System Voltage High
- 168-1 System Voltage Low
- 168-2 System Voltage intermittent
Also, use this procedure if you suspect that the ECM is not receiving the battery supply voltage.
Note: This code can be generated by rapidly cycling the keyswitch. If this occurs, clear the logged diagnostic codes in order to prevent future confusion or an incorrect diagnosis.
The following background information is related to this procedure:
The ECM receives electrical power (battery voltage) through the wiring that is supplied by the engine harness. The ECM input at connector P1:23 (Switched +Battery) receives battery voltage from the keyswitch when the keyswitch is in the ON position or the START position. When the ECM detects battery voltage at this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down.
The cause of an intermittent power supply to the ECM can occur on either the positive side or the negative side of the battery circuit. Both sides are routed from the ECM to the battery. The three connections for the unswitched +battery should be routed through a dedicated protective device (circuit breaker).
The engine ECM requires the keyswitch to be in the ON position in order to maintain communications.
For intermittent problems such as intermittent shutdowns that could be caused by engine wiring, temporarily bypassing the engine wiring may be an effective means of determining the root cause. If the symptoms disappear with the bypass wiring, the engine wiring is the cause of the problem. A means of bypassing engine wiring is explained in this test procedure.
Note: Refer to the Electrical Schematic for proper wiring information.
Test Step 1. Inspect Electrical Connectors And Wiring
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| Illustration 1 | g00885754 |
P1 ECM connector | |
- Thoroughly inspect the harness connector J1/P1 and the Customer Connector J3/P3. Also inspect the connections for the battery and the connections to the keyswitch. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the following connections:
- P1:4 and P1:6 (Unswitched positive battery)
- P1:5 and P1:11 (Negative battery)
- P1:23 (Switched positive battery)
- P1:14 (Remote Shutdown Switch)
- P1:4 and P1:6 (Unswitched positive battery)
- Check the ECM connector (allen head screw) for the proper torque of 2.25 N·m (20 lb in).
- Check the harness and wiring for abrasions and for pinch points from the battery to the ECM. Also, check the harness and wiring for abrasions and for pinch points from the keyswitch to the ECM.
Expected Result:
All connectors, pins, and sockets should be completely coupled and/or inserted. The harness and wiring should be free of corrosion, abrasion, and/or pinch points.
Results:
- OK - All connectors and wiring is proper. Proceed to Test Step 2.
- Not OK - There is a problem with the connectors or wiring.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.
Stop.
Test Step 2. Check the Battery Voltage at the ECM
- 168-02, System Voltage intermittent
- Disconnect engine harness connector P1 from ECM connector J1 and insert a 40-Pin Breakout T.
- Reconnect the harness.
- Turn the keyswitch ON.
- Measure the voltage between terminal 4 (Unswitched positive battery) and terminal 5 (Negative battery).
- Measure the voltage between terminal 6 (Unswitched positive battery) and terminal 11 (Negative battery).
- Measure the voltage between terminal 23 (Switched positive battery) and terminal 5 (Negative battery).
Expected Result:
The measured voltage is between 11.0 VDC and 13.5 VDC for a 12 volt system and between 22.0 VDC and 27.0 VDC for a 24 volt system with no suspected intermittent problems at this time.
Results:
- OK - The ECM is receiving the correct voltage.
Repair: If an intermittent condition is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".
Stop.
- Battery Voltage is out of range - Proceed to Test Step 3.
- Intermittent Or No Voltage - Proceed to Test Step 4.
- Switched Voltage Out Of Range -
Repair: Trace the wiring for the keyswitch from the ECM through the keyswitch circuit to the batteries. Find the problem and repair the problem. Check the circuit protection for the circuit and for the wiring.Verify that the repairs eliminate the problem.
Stop.
Test Step 3. Check The Batteries
- Measure no-load battery voltage at the battery posts.
- Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to Special Instruction, SEHS9249, "Use of 4C-4911 Battery Load Tester for 6, 8 and 12 Volt Lead Acid Batteries" and Special Instruction, SEHS7633, "Battery Test Procedure".
Expected Result:
The batteries pass the load test. The measured voltage is the minimum specification for a 12V or 24V system.
Results:
- OK -
Repair: Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected.
Stop.
- Not OK -
Repair: Recharge or replace the faulty batteries. Verify that the repair eliminates the problem.
Stop.
Test Step 4. Use the Bypass Harness for the Electronic Service Tool to Bypass the Engine Wiring
- Remove the wires from P1:4 (+Battery), P1:6 (+Battery), and P1:23 (Keyswitch Input).
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| Illustration 2 | g00669740 |
Bypass harness | |
Note: The bypass is only for testing. The bypass may be left on the engine temporarily. Remove the bypass before you release the engine to the customer. The ECM will be powered if the bypass switch is activated. The keyswitch must be placed in the ON position. The bypass switch must be activated for normal engine operation. The bypass switch must be deactivated in order to shut down the engine. Deactivate the bypass switch before you perform the following connection.
- Build the bypass circuit in Illustration 2.
Note: Use black electrical tape on all temporary connections. Wrap the connections tightly. Keep the connections clean.
- Connect the battery end of the bypass directly to the +Battery post.
- Insert the sockets of the bypass into P1:4 (+Battery), P1:6 (+Battery), and P1:23 (Switched +Battery).
- Install the temporary switch in the cab.
- Operate the engine and try to duplicate the symptom.
Note: If the symptom only occurs under certain operating conditions, test the engine under those conditions.
Expected Result:
Installing the bypass eliminates the problem.
Results:
- OK - The symptoms disappear when the bypass harness is installed. Also, the symptoms return when the bypass harness is removed. The problem is in the wiring that supplies power to the ECM. Repair the wiring that supplies power to the ECM. Stop.
- Not OK -
Repair: If the problem still exists, temporarily connect a test ECM. Remove all jumpers and replace all connectors. Recheck the system for active diagnostic codes and repeat the Test Step. If the problem is resolved with the test ECM, reconnect the suspect ECM. If the problem returns with the suspect ECM, replace the ECM.Verify that the repair eliminates the problem.
Stop.