C15 – Ignition Key Switch Circuit and Battery Supply Circuit – Test

System Operation Description:
This procedure tests whether proper voltage is being supplied to the Engine Control Module (ECM).

The ECM receives electrical power (battery voltage) through the wiring that is supplied by the vehicle manufacturer. Unswitched battery voltage is supplied through J1:48, J1:52, and J1:53. The negative battery is supplied through J1:61, J1:63, and J1:65. The ECM receives the input from the key switch at P1:70 when the key switch 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. The three connections for the unswitched +Battery should be routed through a dedicated protection device (circuit breaker).

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 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 the battery power to the data link connector is independent of the key switch. Therefore, you will be able to power up the electronic service tool, 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 the electronic service tool 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. 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 key switch.

Test Step 1. Inspect Electrical Connectors and Wiring

A. Thoroughly inspect J1/P1 ECM connector, the battery connections and the connections to the key switch. Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.

B. 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/P1:48, 52, & 53 (Unswitched +Battery)
• J1/P1:61, 63, & 65 (?Battery)
• J1/P1:70 (Key Switch)

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

D. Check the harness and wiring for abrasion and pinch points from the battery to the ECM, and from the key switch 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 4.
• 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 Status for the Key Switch

A. Turn the key switch to the OFF position.
B. Connect the electronic service tool to the data link connector and access the status for “Ignition Key Switch”.
C. Monitor the status while the key switch is being cycled slowly from the ON position to the OFF position.

Note: The electronic service tool may lose communications when the key switch is 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 of the “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 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 – Proceed to Test Step 4.

Test Step 3. Check the Battery Voltage at the Input for the Key Switch

A. Disconnect the J1/P1 ECM connector. Install a 140-2266 Cable (Seventy-Pin Breakout) between the J1 and P1 ECM connectors.

B. Turn the key switch to the ON position.

C. Measure the voltage between P1:70 (Key Switch) and P1:65 (-Battery).
Refer to Illustration 105.

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 ECM is not receiving the correct voltage.

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 Battery Voltage at the ECM

A. Disconnect the P1 ECM connector. Connect a breakout T between the J1 and P1 ECM connectors.

B. Measure the voltage between terminal 48 (Unswitched +Battery) and terminal 61 (-Battery).

C. Measure the voltage between terminal 52 (Unswitched +Battery) and terminal 63 (-Battery).

D. Measure the voltage between terminal 53 (Unswitched +Battery) and terminal 65 (-Battery).

Refer to Illustration 105.

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 5.
• Intermittent Or No Voltage – Proceed to Test Step 6.

Test Step 5. Check the Batteries

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

B. 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

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

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 the key switch circuit.

A. Turn the key switch to the OFF position.

B. Disconnect the J1/P1 ECM connector.

C. Connect a bypass harness to the ECM.

D. Remove the 20 Amp in-line fuse from the +Battery wire of the bypass harness and connect the +Battery and the ?Battery wires directly to the battery posts.

Note: This bypass directly connects the circuit for the key switch to the ECM. The ECM will remain powered until the connection to the Unswitched battery line “+” is disconnected. Remove the 20 Amp fuse from the in-line fuse holder to power down the ECM. Remove the 20 Amp in-line fuse before connecting or disconnecting the bypass harness.

E. Connect the electronic service tool 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 condition after testing.

Expected Result:
Installing the bypass eliminates the problem.

Note: The status of the “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
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.

 

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