G3520B Engines Caterpillar

The master Electronic Control Module (ECM) has internal circuit drivers for the ignition transformers on the left side of the engine. Each circuit driver creates a signal of +108 volts. The signal goes to the high side of the primary circuits of the ignition transformers. The transformers deliver high voltage (8000 to 37,000 volts) to the spark plugs. The external ignition wiring is continuous from the master ECM P2 connector to a bulkhead connector on the left side of the engine. The ignition wiring is inside the engine from the bulkhead connector to the individual transformers for the cylinders with an even number.

The slave ECM has internal circuit drivers for the ignition transformers on the right side of the engine. Each circuit driver creates a signal of +108 volts. The signal goes to the high side of the primary circuits of the ignition transformers. The transformers deliver high voltage (8000 to 37,000 volts) to the spark plugs. The external ignition wiring is continuous from the P4 connector on the slave ECM to a bulkhead connector on the right side of the engine. The ignition wiring is inside the engine from the bulkhead connector to the individual transformers for the cylinders with an odd number.

Some circuit drivers and returns are shared. Therefore, a single problem will generate either only one diagnostic code or multiple codes.

Circuit Drivers

Some circuit drivers send signals to a single cylinder. A high side short circuit will affect only that cylinder.

Some circuit drivers send signals to more than one cylinder. For this reason, a high side short circuit will affect more than one cylinder.

Return Side

The master ECM has internal returns for the ignition transformers on the left side of the engine. Some of the returns consist of groups of terminals that are connected via diodes inside the master ECM. This means that a return short circuit to the +Battery will simultaneously affect all of the cylinders that are grouped.

The slave ECM has internal returns for the ignition transformers on the right side of the engine. Some of the returns consist of groups of terminals that are connected via diodes inside the slave ECM. This means that a return short circuit to the +Battery will simultaneously affect all of the cylinders that are grouped.

For the combinations of cylinders that can be affected by a condition, refer to Table 1.

Because the circuits are in pairs or groups, multiple diagnostic codes can be activated for a single problem. If multiple diagnostic codes are active for the primary ignition, troubleshooting the circuits one at a time is an effective way to find the root cause.

Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.

The most likely causes of the diagnostic code are a poor electrical connection or a problem in a wiring harness. The next likely cause is a problem with an ignition transformer. The least likely cause is a problem with an ECM.

Illustration 1	g00994995
Schematic for the primary ignition on the left side of the engine

Illustration 2	g00903796
Schematic for the primary ignition on the right side of the engine

Test Step 1. Inspect the Electrical Connectors and Wiring

1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

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

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Illustration 3	g00903975
Terminal box for the master ECM (1) J2/P2 connectors for the master ECM (2) 16 amp circuit breaker

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Illustration 4	g00903988
Terminal box for the slave ECM (3) J4/P4 connector for the slave ECM

2. Thoroughly inspect the following connectors:
   • Master ECM J2/P2 connectors

   • J4/P4 connectors for the slave ECM

   1. Check the torque of the Allen head screw for the ECM connectors. The proper torque is 6 ± 1 N·m (55 ± 9 lb in).
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   Illustration 5	g00995001
   Harness side of the master ECM P2 connector (P2-1) Number 2 transformer's circuit driver (P2-2) Number 2 transformer's return (P2-3) Number 12 transformer's circuit driver (P2-4) Number 12 transformer's return (P2-14) Number 4 transformer's circuit driver (P2-15) Number 4 transformer's return (P2-16) Number 16 transformer's circuit driver (P2-17) Number 16 transformer's return (P2-24) Number 8 transformer's circuit driver (P2-25) Number 8 transformer's return (P2-26) Number 20 transformer's circuit driver (P2-27) Number 20 transformer's return (P2-32) Number 10 transformer's circuit driver (P2-33) Number 10 transformer's return (P2-34) Number 18 transformer's circuit driver (P2-35) Number 18 transformer's return (P2-48) Number 6 transformer's circuit driver (P2-49) Number 6 transformer's return (P2-50) Number 14 transformer's circuit driver (P2-51) Number 14 transformer's return

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   Illustration 6	g00995001
   Harness side of the P4 connector for the slave ECM (P4-1) Number 1 transformer's circuit driver (P4-2) Number 1 transformer's return (P4-3) Number 11 transformer's circuit driver (P4-4) Number 11 transformer's return (P4-14) Number 3 transformer's circuit driver (P4-15) Number 3 transformer's return (P4-16) Number 15 transformer's circuit driver (P4-17) Number 15 transformer's return (P4-24) Number 7 transformer's circuit driver (P4-25) Number 7 transformer's return (P4-26) Number 19 transformer's circuit driver (P4-27) Number 19 transformer's return (P4-32) Number 9 transformer's circuit driver (P4-33) Number 9 transformer's return (P4-34) Number 17 transformer's circuit driver (P4-35) Number 17 transformer's return (P4-48) Number 5 transformer's circuit driver (P4-49) Number 5 transformer's return (P4-50) Number 13 transformer's circuit driver (P4-51) Number 13 transformer's return

   2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit of the ignition system.

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Illustration 7	g00903982
Front view of the engine (4) Bulkhead connector for the ignition transformers on the right side of the engine (5) Bulkhead connector for the ignition transformers on the left side of the engine

3. Inspect the bulkhead connectors for the ignition harnesses.

4. Check the ignition harnesses and wiring for abrasion and pinch points from each bulkhead connector to each ECM.

Expected Result:

All 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.

  STOP

Test Step 2. Check for Diagnostic Codes for the Primary Circuit

1. Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

2. Switch the 16 amp circuit breaker ON.

3. Attempt to start the engine. Use Cat ET in order to determine if the following codes are active or logged:
   • 301-05 Ignition Transformer Primary #1 open circuit through 316-05 Ignition Transformer Primary #16 open circuit

   • 1752-05 Ignition Transformer Primary #17 open circuit through 1755-05 Ignition Transformer Primary #20 open circuit

   • 301-06 Ignition Transformer Primary #1 short through 316-06 Ignition Transformer Primary #16 short

   • 1752-06 Ignition Transformer Primary #17 short through 1755-06 Ignition Transformer Primary #20 short

   Note: If a diagnostic code for the primary circuit is logged but not currently active, attempt to repeat the condition that generated the code. Run the engine to full operating temperature.

Expected Result:

None of the above diagnostic codes are active.

Results:

• Active "open circuit" - There is an open in the primary circuit. Proceed to Test Step 5.

• Active "short" - There is a short in the primary circuit. Proceed to Test Step 3.

• Logged only - There may be an intermittent problem in the ignition harness.

  Repair: Perform the following steps:

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  Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring. Do not attempt to remove the valve covers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the valve covers are removed during engine operation. The engine will not operate without the valve covers.

  1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
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  Illustration 8	g00897228
  (1) Valve cover (2) Transformer (3) 2-pin connector (4) Camshaft cover (5) Ignition harness

  2. Remove valve cover (1) for the suspect cylinder. Inspect the harness and the 2-pin connector (3) of transformer (2) .

  3. Remove camshaft cover (4) and inspect ignition harness (5) for abrasion, for exposed wires, and for damage.

  STOP

Test Step 3. Check the Transformer's Primary Circuit and the Secondary Circuit

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Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring. Do not attempt to remove the valve covers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the valve covers are removed during engine operation. The engine will not operate without the valve covers.

1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

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Illustration 9	g00897999
(1) Valve cover (2) Transformer (3) 2-pin connector

2. Remove the valve cover (1) of the suspect cylinder.

3. Disconnect 2-pin connector (3) . Visually inspect the 2-pin connector for corrosion and/or for damage.

4. Remove transformer (2) from the cylinder head.

5. Check the primary circuit and check the secondary circuit according to Systems Operation, Testing and Adjusting, RENR2268, "Ignition Transformer".

Expected Result:

The ignition transformer is within the specifications that are outlined in Systems Operation, Testing and Adjusting, RENR2268, "Ignition Transformer".

Results:

• OK - All of the measurements are correct.

  Repair: Perform the following steps:

  1. Install the spark plug according to the instructions in Operation and Maintenance Manual, "Ignition System Spark Plugs - Check/Adjust/Replace".

  2. Switch the suspect transformer with a transformer from a different cylinder that is known to be good. Install the transformers. Install the valve covers.

  3. Reset the control system. Restart the engine. Clear any logged codes.

  4. Operate the engine. Check for a recurrence of the problem.
  If the problem stays with the suspect transformer, replace the transformer.

  If the problem stays with the suspect cylinder, proceed to Test Step 4.

• Not OK - At least one of the three measurements is incorrect.

  Repair: Replace the ignition transformer. Make sure that you use the correct transformer for the G3520B Engine.

  STOP

Test Step 4. Check for a Short Circuit Between the ECM Connector and the Bulkhead Connector

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There is a strong electrical shock hazard when the crankshaft is rotating. Do not touch the wires that are associated with the ignition system when the engine is cranking or when the engine is running.

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NOTICE
The air inlet, the cylinders, and the exhaust system can be filled with fuel when the gas supply is ON, the ignition system is disabled, and the engine is cranked. The unburned fuel can ignite unexpectedly and cause damage. Turn OFF the gas supply before you perform this step.

1. Shut OFF the fuel supply. Set the engine control to the OFF mode.

2. Disconnect the bulkhead connector that is appropriate for the suspect cylinder.

3. Set the engine control to the START mode and observe the "Active Diagnostic" screen of Cat ET while you crank the engine.

   Note: Additional diagnostic codes will be generated during this test. Disregard the additional codes. Pay attention to the original "short" code.

Expected Result:

The original "short" code is active when the bulkhead connector is disconnected.

Results:

• Yes - The original "short" code was generated after the bulkhead connector was disconnected. The short circuit is probably located in the external harness between the bulkhead connector and the ECM connector.

  Repair: Locate the short circuit. Refer to Troubleshooting, "Inspecting Electrical Connectors". Make repairs, as needed.

  If the condition is not corrected, proceed to Test Step 5.

• No - The original "short" code was not generated after the bulkhead connector was disconnected. The short circuit is in the ignition harness that is inside the engine block. Proceed to Test Step 8.

Test Step 5. Create a Short Circuit in the Ignition Harness

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Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring. Do not attempt to remove the valve covers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the valve covers are removed during engine operation. The engine will not operate without the valve covers.

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NOTICE
The air inlet, the cylinders, and the exhaust system can be filled with fuel when the gas supply is ON, the ignition system is disabled, and the engine is cranked. The unburned fuel can ignite unexpectedly and cause damage. Turn OFF the gas supply before you perform this step.

1. Shut OFF the fuel supply. Set the engine control to the OFF/RESET mode.

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Illustration 10	g00720019
(1) Valve cover (2) 2-pin connector for the ignition harness

2. Remove valve cover (1) for the suspect cylinder.

3. Disconnect the 2-pin connector (2) . Inspect the connectors of the harness and of the transformer. Verify that the connectors do not have damage or corrosion. Inspect the harness. Verify that the harness does not have damage or corrosion.

4. Install a jumper wire into the terminals of the 2-pin connector on the ignition harness.

5. Set the engine control to the START mode and observe the "Active Diagnostic" screen of Cat ET while you crank the engine. Look for the original "open circuit" code.

Expected Result:

The original "open circuit" code is active.

Results:

• Yes - The original "open circuit" code was generated after a short circuit was created in the ignition harness. The ECM did not detect the jumper wire. Proceed to Test Step 6.

• No - Cat ET displayed an active "short" diagnostic code after a short circuit was created in the ignition harness. The harness and the ECM are OK.

  Repair: Perform the following steps:

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  There is a strong electrical shock hazard when the crankshaft is rotating. Do not touch the wires that are associated with the ignition system when the engine is cranking or when the engine is running.

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  NOTICE
  The air inlet, the cylinders, and the exhaust system can be filled with fuel when the gas supply is ON, the ignition system is disabled, and the engine is cranked. The unburned fuel can ignite unexpectedly and cause damage. Turn OFF the gas supply before you perform this step.

  1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

  2. Remove the jumper wire from the 2-pin connector of the ignition harness. Thoroughly inspect the connectors for the transformer. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  3. Connect the ignition harness to the transformer.

  4. Set the engine control to the START mode and observe the "Active Diagnostic" screen of Cat ET while you crank the engine. Look for the original "open circuit" code.

  5. If the original "open circuit" code is generated, set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

  6. Replace the transformer. Make sure that you use the correct transformer for the G3520B Engine.

  7. Clear all of the logged diagnostic codes.

  STOP

Test Step 6. Check the Engine Harness for an Open Circuit

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There is a strong electrical shock hazard when the crankshaft is rotating. Do not touch the wires that are associated with the ignition system when the engine is cranking or when the engine is running.

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NOTICE
The air inlet, the cylinders, and the exhaust system can be filled with fuel when the gas supply is ON, the ignition system is disabled, and the engine is cranked. The unburned fuel can ignite unexpectedly and cause damage. Turn OFF the gas supply before you perform this step.

1. Shut OFF the fuel supply. Set the engine control to the OFF/RESET mode.

2. Disconnect the bulkhead connector that is appropriate for the suspect cylinder.

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Illustration 11	g00720061
Terminals on the bulkhead connector of the ignition harness

3. Install the ends of the jumper wire into the terminals of the connector on the external engine harness side of the bulkhead connector for the suspect cylinder.

   The cylinders and the terminals are identified in Table 2 and Illustration 11.

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   Table 2

   Cylinders and Corresponding Terminals of the Bulkhead Connector for the Ignition Harness
   Cylinder	Terminals for the Circuit Driver	Return Terminals
   1	A	B
   2	A	B
   3	C	D
   4	C	D
   5	K	L
   6	K	L
   7	P	R
   8	P	R
   9	S	T
   10	S	T
   11	X	Z
   12	X	Z
   13	a	b
   14	a	b
   15	e	f
   16	e	f
   17	n	p
   18	n	p
   19	r	s
   20	r	s

4. Set the engine control to the START mode and observe the "Active Diagnostic" screen of Cat ET while you crank the engine. Look for the original "open circuit" diagnostic code.

Expected Result:

The original "open circuit" diagnostic code is not active. However, a "short" diagnostic code is generated for the suspect cylinder.

Results:

• Yes - When the jumper wire was installed into the harness, the original "open circuit" diagnostic code was not active. However, a "short" diagnostic code was generated for the suspect cylinder. The external engine harness and the ECM are OK. The internal ignition harness in the engine block has an open circuit.

  Repair: Perform the following steps:

  1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

  2. Remove the camshaft covers from the bank of the engine with the suspect cylinder.

  3. Inspect the internal ignition harness. Verify that the harness does not have abrasion, exposed wires, or other damage. Be sure to inspect the harness inside the front of the engine. Repair the harness, when possible. Replace the harness, if necessary.

  STOP

• No - When the jumper wire was installed into the external engine harness, the original "open circuit" diagnostic code was generated. The ECM did not detect the jumper wire. The open circuit is probably in the external engine harness.

  Repair: Refer to Troubleshooting, "Inspecting Electrical Connectors". Make repairs, as needed.

  If the condition is not corrected, proceed to Test Step 7.

Test Step 7. Check the ECM

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There is a strong electrical shock hazard when the crankshaft is rotating. Do not touch the wires that are associated with the ignition system when the engine is cranking or when the engine is running.

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NOTICE
The air inlet, the cylinders, and the exhaust system can be filled with fuel when the gas supply is ON, the ignition system is disabled, and the engine is cranked. The unburned fuel can ignite unexpectedly and cause damage. Turn OFF the gas supply before you perform this step.

1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

2. Disconnect the ECM connector that is appropriate for the suspect cylinder. If the suspect cylinder has an even number, disconnect the P2 connector. If the suspect cylinder has an odd number, disconnect the P4 connector.

3. Thoroughly inspect the connectors. Verify that the connectors do not have corrosion, moisture, or other damage. Make repairs, if necessary.

4. Use a 151-6320 Wire Removal Tool to remove wiring from the ECM connector. The removal of the wiring depends on the original diagnostic code.
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   Illustration 12	g00995001
   ECM P2 or P4 connector

   Note: For identification of the terminals, refer to Illustration 12 and Table 3.

   1. If you are troubleshooting a "short" diagnostic code, remove the wire from the terminal for the circuit driver of the suspect cylinder.

   2. If you are troubleshooting an "open circuit" diagnostic code, remove the wires from the terminal for the circuit driver AND from the return of the suspect cylinder. Then install the ends of the jumper wire into the terminals for the removed wires. This will replace the ignition wiring with a short circuit.
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      Table 3

      Cylinders and Corresponding Terminals of the ECM Connector for the Ignition Harness
      Cylinder	Terminals for the Circuit Driver	Return Terminals
      1	1	2
      2	1	2
      3	14	15
      4	14	15
      5	48	49
      6	48	49
      7	24	25
      8	24	25
      9	32	33
      10	32	33
      11	3	4
      12	3	4
      13	50	51
      14	50	51
      15	16	17
      16	16	17
      17	34	35
      18	34	35
      19	26	27
      20	26	27

5. Reconnect all of the connectors. If any valve covers were removed, install the valve covers.

6. Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.

7. Set the engine control to the START mode and observe the "Active Diagnostic" screen of Cat ET while you crank the engine.

Expected Result:

An "open circuit" diagnostic code is generated for the circuit after removal of the wire for the circuit driver.

A "short" diagnostic code is generated for the circuit with the installed jumper wire.

Results:

• Yes - A diagnostic code was generated according to the Expected Result. The ECM is operating correctly. There is a problem with the ignition harness.

  Repair: Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF. Repair the harness, when possible. Replace the harness, if necessary.

  STOP

• No - A diagnostic code was NOT generated according to the Expected Result. There is a problem with the ECM.

  Repair: Replace the ECM that is appropriate for the suspect cylinder. Follow the instructions in Troubleshooting, "Replacing the ECM".

  STOP

Test Step 8. Check the Ignition Transformer for a Short Circuit

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Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring. Do not attempt to remove the valve covers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the valve covers are removed during engine operation. The engine will not operate without the valve covers.

Show/hide table

NOTICE
The air inlet, the cylinders, and the exhaust system can be filled with fuel when the gas supply is ON, the ignition system is disabled, and the engine is cranked. The unburned fuel can ignite unexpectedly and cause damage. Turn OFF the gas supply before you perform this step.

1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

2. Remove the valve cover for the suspect cylinder.

3. Inspect the ignition harness. Verify that the harness does not have abrasion, exposed wires, or other damage.

4. Disconnect the ignition harness from the transformer. Thoroughly inspect the 2-pin connector on the transformer.

5. Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.

6. Do not reconnect the transformer. Set the engine control to the START mode and observe the "Active Diagnostic" screen of Cat ET while you crank the engine.

Expected Result:

An "open circuit" diagnostic code is generated for the circuit with the disconnected transformer.

Results:

• Yes - An "open circuit" diagnostic code was generated for the circuit with the disconnected transformer.

  Repair: Perform the following steps:

  Show/hide table

  There is a strong electrical shock hazard when the crankshaft is rotating. Do not touch the wires that are associated with the ignition system when the engine is cranking or when the engine is running.

  Show/hide table

  NOTICE
  The air inlet, the cylinders, and the exhaust system can be filled with fuel when the gas supply is ON, the ignition system is disabled, and the engine is cranked. The unburned fuel can ignite unexpectedly and cause damage. Turn OFF the gas supply before you perform this step.

  1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

  2. Thoroughly inspect the 2-pin connectors for the internal ignition harness and the transformer. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  3. Reconnect the internal ignition harness to the transformer.

  4. Switch the 16 amp circuit breaker ON. Set the engine control to the START mode and observe the "Active Diagnostic" screen of Cat ET while you crank the engine.

  5. If the "short circuit" code is generated again, set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF. Replace the transformer. Make sure that you use the correct transformer for the G3520B Engine.

  6. Clear all of the logged diagnostic codes.

  STOP

• No - An "open circuit" diagnostic code was not generated for the circuit with the disconnected transformer. The short circuit is in the internal ignition harness.

  Repair: Perform the following steps:

  1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

  2. Remove the camshaft covers from the bank of the engine with the suspect cylinder.

  3. Inspect the internal ignition harness. Verify that the harness does not have abrasion, exposed wires, or other damage. Repair the harness, when possible. Replace the harness, if necessary.

  STOP