3126B and 3126E On-highway Engines Caterpillar

This procedure tests whether proper voltage is supplied by vehicle wiring. Use this procedure if any one of the following diagnostic codes are logged several times:

• 168-02 Intermittent Battery (51)

• 43-02 Ignition Keyswitch Fault (71)

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 ignition keyswitch. Some control modules on the vehicle require this action in order to prompt flash codes. If this occurs, clear the logged diagnostic codes in order to prevent future confusion or an incorrect diagnosis.

The ECM receives electrical power (battery voltage) through the wiring that is supplied by the vehicle manufacturer. The ECM input at connector P1 terminal 70 (ignition keyswitch) receives battery voltage from the ignition keyswitch when the ignition 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 (unswitched +battery) or the negative side (−battery). Both sides are routed from the ECM to the battery. The two connections for the unswitched +Battery must be routed through a dedicated protection circuit.

Some vehicles may be equipped with an engine protection shutdown system or an idle timer shutdown system that interrupts electrical power to the ECM in order to shut down the engine. Also, some vehicles may be equipped with an engine protection shutdown system or an idle timer shutdown system that interrupts electrical power to the ignition keyswitch. The engine protection shutdown system can be an aftermarket device and the idle timer shutdown system can be external to the ECM. Some of these systems will not supply power to the ECM until one of the following conditions is met:

• The engine is cranked.

• The engine oil pressure achieves acceptable limits.

• An override button is pressed.

Keep in mind that these devices may be the cause of intermittent power to the ECM.

Usually, battery power to the cab data link connector is available and the battery power to the cab data link connector is independent of the ignition keyswitch. Therefore, you will be able to power up ET, but you may not be able to communicate with the engine ECM. The engine ECM requires the ignition keyswitch to be in the ON position in order to maintain communications. The ECM may power down a short time after connecting ET if the ignition keyswitch is in the OFF position. This is normal. Refer to Troubleshooting, "ATA (SAE J1587 / J1708) Data Link Circuit - Test".

For intermittent problems such as intermittent shutdowns that could be caused by vehicle wiring, temporarily bypassing the vehicle wiring may be an effective means of determining the root cause. If the symptoms disappear with the bypass wiring, the vehicle wiring is the cause of the problem. A means of bypassing vehicle wiring is explained in this test procedure. This is especially important for vehicles that do not provide dedicated circuits for the unswitched battery and the connections for the ignition keyswitch.

Illustration 1	g00742658
Schematic for ECM battery circuit

Illustration 2	g00640974
Terminal locations for ECM

Test Step 1. Inspect Electrical Connectors and Wiring.

1. Thoroughly inspect ECM vehicle harness connector J1/P1, the battery connections and the connections to the ignition keyswitch. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the following connections:
   • Unswitched +battery (terminals 52 and 53)

   • −Battery (terminals 65 and 67)

   • Ignition keyswitch (terminal 70)

3. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

4. Check the harness and wiring for abrasion and pinch points from the battery to the ECM, and from the ignition keyswitch to the ECM.

Expected Result:

All connectors, pins and sockets should be completely coupled and/or inserted and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

• OK, Troubleshooting a 43-02 Code - Proceed to Test Step 2.

• OK, Troubleshooting a 168-02 Code - Proceed to Test Step 3.

• 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. Use ET to Check the Ignition keyswitch.

1. Turn the ignition keyswitch to the OFF position.

2. Connect ET to the cab data link connector and access the status screen that shows the status of the ignition keyswitch.

3. Monitor the status of the ignition keyswitch while the ignition keyswitch is being cycled slowly from the ON position to the OFF position.

   Note: ET may indicate that a new ECM has been detected. This condition is normal, due to a powerdown of the ECM with the ignition keyswitch in the OFF position.

   Note: Cycling the ignition keyswitch several times may cause additional 43-02 faults to be logged. This is normal. Clear any logged faults.

Expected Result:

The status of the ignition keyswitch changes from "On" with the ignition keyswitch in the ON position to "Off" with the ignition keyswitch in the OFF position.

Results:

• YES - The input for the ignition keyswitch is functioning properly at this time.

  Repair: If an intermittent connection is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect". Excessive cycling of the ignition keyswitch can cause this fault to be logged. This is normal. Clear any logged faults.

  STOP

• NO - Proceed to Test Step 3.

Test Step 3. Check the Battery Voltage at the ECM.

Perform Steps A, B, and C if the following diagnostic code is active or logged:

• 168-02 Intermittent Battery (51)

1. Disconnect vehicle harness connector P1 from ECM connector J1 and insert a breakout T.

2. Measure the voltage between vehicle harness connector P1 terminal 52 (unswitched +battery) and terminal 65 (-battery).

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Illustration 3	g00640981
ECM Breakout T-connector

3. Measure the voltage from vehicle harness connector P1 terminal 53 (unswitched +battery) and terminal 67 (-battery).

   Refer to Illustration 3 for the ECM breakout T-connector.

   Perform Steps D, E, and F if the following diagnostic code is active or logged:

   • 43-02 Ignition keyswitch Fault (71)

4. Disconnect vehicle harness connector P1 from ECM connector J1 and insert a breakout T.

5. Turn the ignition keyswitch to the ON position.

6. Measure the voltage between vehicle harness connector P1 terminal 70 (Ignition keyswitch) and terminal 65 (-battery).

   Refer to Illustration 3 for the ECM breakout T-connector.

Expected Result:

For 12 Volt Systems, the measured voltage is a constant 11.0 to 13.5 VDC with no suspected intermittent problems at this time.

For 24 Volt Systems, the measured voltage is a constant 22.0 to 27.0 VDC 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 4.

• Intermittent Or No Voltage - Proceed to Test Step 5.

• keyswitch Voltage Out Of Range -

  Repair: Trace the wiring for the ignition 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 the wiring. Refer to the vehicle service manual for instructions on troubleshooting the circuit for the ignition keyswitch.Verify that the repairs eliminate the problem.

  STOP

Test Step 4. Check the Batteries.

1. Measure no-load battery voltage at the battery posts.

2. 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. For 12 Volt Systems, the measured voltage is at least 11.0. For 24 Volt Systems, the measured voltage is at least 22.0.

Results:

• YES -

  Repair: Refer to the vehicle service manual for instructions on troubleshooting the vehicle wiring harness. Troubleshoot the vehicle wiring harness and repair the vehicle wiring harness, as required. Verify that the repairs eliminate the problem.

  STOP

• NO -

  Repair: Recharge or replace the faulty batteries. Verify that the repair eliminates the problem.

  STOP

Test Step 5. Bypass the Vehicle Harness

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Batteries give off flammable fumes which can explode. To avoid injury or death, do not strike a match, cause a spark, or smoke in the vicinity of a battery.

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NOTICE
Do not connect the bypass harness to the battery until all three of the 10 Amp in-line fuses have been removed from the +Battery line. If the fuses are not removed before connection to the battery a spark may result.

Note: This bypass harness is only for test applications. This bypass harness must be removed before the vehicle is released to the customer. The bypass harness can be used in order to determine if the cause of the intermittent problem is interruptions in battery power to the ECM or to the keyswitch circuit.

1. Turn the keyswitch to the OFF position.

2. Disconnect the J1/P1 ECM connector.

3. Connect the bypass harness to the ECM:

   1. Connect the 70-pin connector of the 167-9225 Harness (SERVICE TOOL ADAPTER) to the J1 ECM connector.

   2. Connect the 9-pin connector for the adapter cable to the data link connector that is for Cat ET.

   3. Remove all three of the 10 Amp in-line fuses from the +Battery wire.

      Note: This bypass directly connects the circuit for the keyswitch to the ECM. The ECM will remain powered until the connection to the unswitched battery line "+" is disconnected. Remove all three of the 10 Amp in-line fuses from the in-line fuse holder to power down the ECM. Do not connect the bypass to the battery posts or do not remove the bypass from the battery posts without first removing the 10 Amp in-line fuses.

   4. Connect the red cable clamp to the +Battery terminal.

   5. Connect the black cable clamp to the −Battery terminal.

4. Connect Cat ET to the data link connector of the bypass harness and verify that communication can be established.

   Note: Remove the bypass harness and restore all wiring to the original configuration after testing.

Expected Result:

Installing the bypass eliminates the problem.

Note: The status of the "Ignition keyswitch" will always indicate "On" while the bypass harness is installed.

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 vehicle wiring that supplies power to the ECM. Check for aftermarket engine protection switches that interrupt power. Send the vehicle to the OEM dealer to repair.STOP

• Not OK -

  Repair: Connect the bypass to another battery and verify if the problem is resolved. If the problem is resolved, the problem is with the vehicle batteries.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 this 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.Refer to Troubleshooting, "Replacing the ECM".Verify that the repair eliminates the problem.

  STOP