G3500 A3 Engines Caterpillar

Use this procedure to troubleshoot the following diagnostic codes:

• 168-2 Electrical System Voltage erratic, intermittent, or incorrect

• 336-2 Engine Control Switch erratic, intermittent, or incorrect

This procedure tests whether proper voltage is supplied to the Electronic Control Module (ECM). This procedure also verifies the proper operation of the engine control.

The cause of a problem with the power supply to a component can occur on either the positive side or on the negative side of the circuit.

The 24 VDC power supply for the engine can be provided by a battery or by an electrical power supply. If the power is provided by an electrical power supply, the maximum allowable ripple voltage is 150 mV AC peak to peak. The minimum requirement for the power supply is 22 VDC at 20 amperes. The wiring from the power supply to a component must provide a maximum voltage drop of 1.0 VDC.

The keyswitch power is provided to the ECM at terminal P1-70. This terminal receives battery voltage from the engine control when the control is in the START position, in the COOLDOWN/STOP position, or in the AUTO position. When the ECM detects voltage at this input, the ECM will power up. When voltage is removed from this input, the ECM will power down after the engine has shut down.

The 168-2 diagnostic code indicates that the supply voltage is intermittent or low while the engine is running. If the supply voltage drops to zero and stays at zero, the ECM will not log this code. The engine will shut down.

The 336-2 diagnostic code indicates that the ECM has detected a problem with the circuit for the engine control switch.

This procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.

Illustration 1	g01437340
Schematic for the electrical power supply

Test Step 1. Inspect the Electrical Connectors and Wiring

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Illustration 2	g01392829
Location of the connectors for the electrical power supply (1) J1/P1 ECM connectors (2) Interface box

1. Set the engine control to the OFF/RESET position.

   Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".

2. Thoroughly inspect ECM connector (1) for damage, for corrosion, and for moisture. Also, thoroughly inspect each connection and the condition of each fuse that is located in interface box (2).

   1. Check the allen head screw for each of the ECM connectors for the proper torque.
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      Illustration 3	g01392896
      Terminal locations at the P1 ECM connectors for the electrical power supply (P1-52) +Battery (P1-53) +Battery (P1-55) +Battery (P1-57) +Battery (P1-63) −Battery (P1-65) −Battery (P1-67) −Battery (P1-69) −Battery (P1-70) Keyswitch

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      Illustration 4	g01392868
      Terminal locations at the interface box for the electrical power supply (7) Keyswitch (11) −Battery (12) +Battery (F1) Main fuse (15 Amp) (F2) Fuse for the throttle actuator (10 Amp) (F3) Fuse for the Air/Fuel Ratio Control (AFRC) (10 Amp)

   2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the electrical power supply:

   3. Check the harness and wiring for abrasion and for pinch points from the power supply to the ECM and from the engine control to the ECM.

Expected Result:

All of the connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.

Results:

• OK - The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - The components are not in good condition and/or at least one connection is improper.

  Repair: Perform the necessary repairs and/or replace parts, if necessary. Ensure that all of the seals are properly installed. Make sure that the connectors are properly fastened. Verify that the repair has eliminated the problem.

  STOP

Test Step 2. Check the Voltage at the Power Supply and at the ECM

1. Make sure that the engine will not crank during this procedure. For an engine with an electric starting motor, make sure that the battery cables are disconnected from the motor. For an engine with an air starting motor system, confirm that the pressurized air supply is turned off. Ensure that the air pressure is released from the system.

   Note: If a power supply is used instead of batteries, the minimum voltage for the power supply is 22 VDC at 20 amperes. Troubleshoot the power supply if the voltage is less than 22 VDC or more than 29 VDC.

2. Measure the voltage at the terminals for the power supply. Record the voltage.

3. Insert two 7X-1710 Multimeter Probes into the harness side of the P1 ECM connector. Insert the first probe into terminal P1-52. Insert the second probe into terminal P1-63. Connect a multimeter to the probes.

4. Measure the power supply voltage at the P1 connector. During the measurement, wiggle the harness in order to check for an intermittent problem. Be sure to wiggle the harness near each of the connections.

Expected Result:

The voltage that is measured at the terminals for the power supply is at least 22 VDC. The voltage that is measured at the P1 ECM connector is within 1 VDC of the voltage that was measured at the terminals for the power supply. The voltage measurements are constant.

Results:

• OK - The ECM is receiving the correct voltage at the P1 ECM connector.

  Repair: Remove the probes from the P1 ECM connector.

  Proceed to Test Step 3.

• Not OK - The ECM is not receiving the correct voltage at the P1 ECM connector.

  Repair: Perform the following procedure:

  1. Remove the probes from the P1 ECM connector.

  2. Refer to the appropriate schematic. Use a voltmeter to check the wiring. Locate the source of the voltage drop.

  3. Perform the necessary repairs.

  STOP

Test Step 3. Check for the Proper Operation of the Engine Control

1. Make sure that the engine will not crank during this procedure. For an engine with an electric starting motor, ensure that the battery cables are disconnected from the motor. For an engine with an air starting motor system, confirm that the pressurized air supply is OFF. Make sure that the air pressure is released from the system.

2. Establish communication between Caterpillar Electronic Technician (ET) and the ECM.

   Note: An E225 Engine Overcrank and/or an E233 Low Engine Pre-Lube Pressure may be generated during this test step. After you have completed this test step, clear the events from the "Logged Events" screen of Cat ET.

3. Observe the "Active Diagnostic" screen on Cat ET and set the engine control to the COOLDOWN/STOP position, the START position, and the AUTO position. Look for an active 336-2 diagnostic code. Repeat this step several times.

Expected Result:

A 336-2 diagnostic code was not activated when the engine control was set to the COOLDOWN/STOP position, the START position, and the AUTO position.

Results:

• OK - A 336-2 diagnostic code was not activated.

  Repair: The inputs from the engine control are correct. There may be an intermittent problem in the harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Inspecting Electrical Connectors" for troubleshooting information.

  STOP

• Not OK - A 336-2 diagnostic code was activated. The ECM has detected a problem with the input signals from the engine control. Proceed to Test Step 4.

Test Step 4. Check the Circuit of the Engine Control

1. Make sure that the engine will not crank during this procedure. For an engine with an electric starting motor, make sure that the battery cables are disconnected from the motor. For an engine with an air starting motor system, confirm that the pressurized air supply is OFF. Ensure that the air pressure is released from the system.

2. Set the engine control to the OFF/RESET position.

3. Insert two 7X-1710 Multimeter Probes into the harness side of the P1 ECM connector. Insert the first probe into terminal P1-31. Insert the second probe into terminal P1-61. Connect a multimeter to the probes.

   Note: An E225 Engine Overcrank and/or an E233 Low Engine Pre-Lube Pressure may be generated during the test. After you have completed the test, clear the events from the "Logged Events" screen of Cat ET.

   Note: During these measurements, wiggle the harness in order to check for an intermittent problem. Wiggle the harness near each of the connections.

4. Set the engine control to the COOLDOWN/STOP position and measure the voltage between terminal P1-31 and terminal P1-61 at the ECM connector. The correct voltage measurement is less than one volt.

5. Remove the probe from terminal P1-61 and insert the probe into terminal 62.

6. Set the engine control to the START position and measure the voltage between terminal P1-31and terminal P1-62 at the ECM connector. The correct voltage measurement is less than one volt.

7. Remove the probe from terminal P1-62 and insert the probe into terminal P1-64.

8. Set the engine control to the AUTO position and measure the voltage between terminal P1-31 and terminal P1-64 at the ECM connector. The correct voltage measurement is less than one volt.

9. Remove the probe from terminal P1-31 and insert the probe into terminal P1-69. Remove the probe from terminal P1-64 and insert the probe into terminal P1-70.

10. Set the engine control to the COOLDOWN/STOP position and measure the voltage between terminal P1-69 and terminal P1-70 at the ECM connector. The correct voltage measurement is at least +20 VDC.

11. Set the engine control to the START position and measure the voltage between terminal P1-69 and terminal P1-70 at the ECM connector. The correct voltage measurement is at least +20 VDC.

12. Set the engine control to the AUTO position and measure the voltage between terminal P1-69 and terminal P1-70 at the ECM connector. The correct voltage measurement is at least +20 VDC.

Expected Result:

The voltage checks are within the specifications.

Results:

• OK - The voltage checks are within the specifications. Remove the probes from the ECM connector. Start the engine and run the engine. If the original problem is not resolved, the ECM may have a problem.

  Repair: Temporarily install a new ECM. Refer to Troubleshooting, "Replacing the ECM".

  If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP

• Not OK - The voltage is not correct at the ECM connector.

  Repair: Perform the following steps:

  1. Set the engine control to the OFF/RESET position.

  2. Disconnect the wires for the COOLDOWN/STOP, START, and AUTO positions from the engine control.

  3. Use an ohmmeter to check the continuity at the engine control. Set the control to each position in order to check the continuity.

  4. If the engine control is faulty, replace the control. If the problem is not resolved, there is a problem in the harness. Repair the harness, when possible. Replace the harness, if necessary.

  STOP