The following diagnostic codes indicate a problem with the power supply to the Electronic Control Module (ECM):
- 168-02 ECM Battery Power Intermittent
- 43-02 Key Switch Fault
Note: This code can be generated by rapidly cycling the key switch. 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 following background information is related to this procedure:
The ECM receives electrical power (battery voltage) through the wiring that is supplied by the vehicle manufacturer. The ECM input at connector P1:70 (Ignition Key Switch) receives battery voltage from the key switch when the key switch is in the ON position or in 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 Unswitched +Battery connections 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 a system that interrupts electrical power to the key switch. 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 data link connector is available and this battery power is independent of the key switch. Therefore, you will be able to power up the Caterpillar Electronic Technician (Cat ET), but you may not be able to communicate with the engine ECM. The engine ECM requires the key switch to be in the ON position in order to maintain communications. The ECM may power down a short time after connecting to Cat ET if the key switch is in the OFF position. This is normal.
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. This is especially important for vehicles that do not provide dedicated circuits for the unswitched battery and the key switch.
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| Illustration 1 | g00779064 |
Schematic for ECM battery circuit | |
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| Illustration 2 | g00640974 |
Terminal locations for ECM | |
Test Step 1. Inspect Electrical Connectors and Wiring
- Thoroughly inspect the J1/P1 ECM connector, the battery connections and the connections to the key switch. 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:
- J1/P1:52 & 53 (Unswitched +Battery)
- J1/P1:65 & 67 (−Battery)
- J1/P1:70 (Ignition Key Switch)
- J1/P1:52 & 53 (Unswitched +Battery)
- Check the allen head screws on the ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Check the harness and wiring for abrasion and for pinch points from the battery to the ECM, and from the key switch to the ECM.
Expected Result:
All connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK - The connectors and wiring are OK but there may be a problem with the keyswitch. Proceed to Test Step 2.
- OK - The connectors and wiring are OK but there may be a problem with the battery voltage. Proceed to Test Step 3.
- Not OK - There is a problem with the connectors and/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 Status for the Ignition Key Switch
- Turn the key switch to the OFF position.
- Connect Cat ET to the data link connector and access the status screen that shows the status for "Ignition Key Switch".
- Monitor the status for "Ignition Key Switch" while the key switch is being cycled slowly from the ON position to the OFF position.
Note: Cat ET may indicate that a new ECM has been detected. This condition is normal, due to a powerdown of the ECM with the key switch in the OFF position.
Note: Cycling the key switch several times may cause additional 43-02 faults to be logged. This is normal. Clear any logged faults.
Expected Result:
The status for "Ignition Key Switch" changes from "On" with the key switch in the ON position to "Off" with the key switch in the OFF position.
Results:
- OK - The key switch input is functioning properly at this time.
Repair: If an intermittent connection is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect". Excessive cycling of the key switch can cause this fault to be logged. This is normal. Clear any logged faults.
STOP
- Not OK - The key switch input is not functioning properly. 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 ECM Battery Power Intermittent
- Insert a 140-2266 Cable (Seventy-Pin Breakout) between the J1 and P1 ECM connector.
- Measure the voltage between P1:52 (Unswitched +Battery) and P1:65 (-Battery).
- Measure the voltage between P1:53 (Unswitched +Battery) and P1:67 (-Battery).
Refer to Illustration 3.
Perform Steps D, E, and F if the following diagnostic code is active or logged:
- 43-02 Key Switch Fault
- 43-02 Key Switch Fault
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| Illustration 3 | g00640981 |
ECM Breakout T-connector | |
- Insert a 140-2266 Cable (Seventy-Pin Breakout) between the J1 and P1 ECM connector.
- Turn the key switch to the ON position.
- Measure the voltage between P1:70 (Ignition Key Switch) and P1:65 (-Battery).
Refer to Illustration 3.
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
- Not OK - The battery voltage is intermittent or there is no voltage. Proceed to Test Step 5.
- - The voltage for the key switch is out of the acceptable range.
Repair: Trace the wiring for the key switch from the ECM through the key switch 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 key switch.Verify that the repairs eliminate the problem.
STOP
Test Step 4. 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. 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:
- OK - The voltage is within the acceptable range.
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
- Not OK - The voltage is out of the acceptable range.
Repair: Recharge or replace the faulty batteries. Verify that the repair eliminates the problem.
STOP
Test Step 5. Bypass the Vehicle Harness
- Turn the key switch to the OFF position.
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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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- Disconnect the J1/P1 ECM connector.
- Connect the 70-Pin connector of the 167-9225 Harness (Service Tool Adapter) to the ECM J1 connector. Connect the harnesses 9-pin connector to the Cat ET service tool adapter. Connect the red cable clamp to the +Battery. Connect the black cable clamp to the −Battery terminal.
- Connect Cat ET to the data link connector of the bypass harness and verify that communication is established.
- Restore all wiring to the original condition after testing.
Expected Result:
Installing the bypass eliminates the problem.
Note: The status for "Ignition Key Switch" 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 - The symptoms did not disappear.
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 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