Use this procedure to troubleshoot the following diagnostic codes:
- 401-5 through 416-5 Ignition Transformer Secondary #1 current below normal through Ignition Transformer Secondary #16 current below normal
- 401-6 through 416-6 Ignition Transformer Secondary #1 current above normal through Ignition Transformer Secondary #16 current above normal
The ignition transformers initiate combustion by providing high voltage to the spark plugs. The positive output from the secondary circuit of the transformer is at the connection for the terminal of the transformer and the terminal of the spark plug. The transformers are located underneath the valve covers. Each transformer is grounded to a valve cover via a ground spring.
The secondary circuit of the transformer provides an initial 8,000 to 37,000 volts to the spark plug. This voltage ionizes the spark plug gap. This voltage is then reduced to about 1000 volts. The total duration of the spark is approximately 400 microseconds.
The Electronic Control Module (ECM) can diagnose the primary circuit of the ignition transformers for open circuits and/or for short circuits. Secondary open circuits and short circuits will not directly shut down the engine. However, these conditions may lead to misfire which can cause lugging of the engine. Lugging of the engine can cause a shutdown.
Caterpillar spark plugs are high voltage devices with internal resistors. The spark plugs operate at a voltage that is greater than 5,000 volts.
Most ignition systems are not affected by resistance in the secondary circuit. If a measurement of the resistance is desired, a megohmmeter must be used. A low voltage multimeter will not provide a reliable reading of the resistance because oxidation of the spark plug's internal components will affect the readings of those meters.
Test Step 1. Check the Status Screen of Caterpillar Electronic Technician (ET) for the Output of the Secondary Circuits of the Transformers
- Establish communication between Cat ET and the ECM. Refer to Troubleshooting, "Electronic Service Tools", if necessary.
Note: The "% Secondary Voltage" display is provided as an indicator of the spark plugs' condition. With new spark plugs, the "% Secondary Voltage" value will be low. As the spark plug is used and the wear on the gap increases, the "% Secondary Voltage" value will increase. The increase of the wear on the gap may cause the cylinder to misfire, even though the "% Secondary Voltage" has not reached 100 percent.
- Set up a status screen on Cat ET in order to monitor the "Transformer Secondary Output Voltage Percentage" for all of the cylinders. Two status screens are required on 12 cylinder engines and 16 cylinder engines in order to monitor all of the cylinders.
- Start the engine. Apply the normal load at rated speed. Allow the engine to warm up to normal operating temperature.
- Observe the value of the output for the secondary circuit of each transformer.
Expected Result:
The displayed value of the output for the secondary circuit of each transformer is between 0 and 90 percent. The exhaust temperatures for each cylinder are approximately equal to the engine's average exhaust port temperature.
Results:
- OK - The displayed value of the output for the secondary circuit of each transformer is between 0 and 90 percent. The exhaust port temperatures are OK. The ignition system components are operating properly.
Repair: Investigate other possible root causes of the problem. Troubleshoot the symptom. Refer to Troubleshooting, "Troubleshooting Without A Diagnostic Code".
STOP
- Not OK - There is a diagnostic code for the secondary ignition for a cylinder. That cylinder's exhaust port temperature is at least
20 °C (68 °F) below the average temperature of the engine's exhaust ports. The ignition system components require maintenance. Proceed to Test Step 2.
Test Step 2. Inspect the Transformer
- Set the engine control to the OFF/RESET position.
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Illustration 1 g01091169 Section view of the side of a cylinder head
(1) Valve cover
(2) 2-pin connector
(3) Transformer - Remove valve cover (1) of the suspect cylinder.
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NOTICE Pulling on the wiring harness may break the wires. Do not pull on the wiring harness.
- Disconnect 2-pin connector (2). Remove transformer (3) from the engine.
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Illustration 2 g01256751 Ignition transformer and extension
(3) Transformer
(4) Screws for the ground spring
(5) Ground spring
(6) Spacer
(7) Seal
(8) Secondary terminal for the spark plug
(9) Extension
(10) O-ring seal - Inspect the body of transformer (3) and ground spring (5). Verify that there is no corrosion nor damage. Verify that the screws for ground spring (4) are secure.
- Inspect seal 7 for cracks.
- Inspect secondary terminal (8) for corrosion and/or for damage.
- Inspect O-ring seal (10) inside extension (9) for damage.
- Check for a secure connection between the transformer and the spark plug.
Note: Pin holes are caused by misfire in the engine that does not generate a diagnostic code.
- Check extension (9) near spacer (6) for signs of pin holes and/or of arcing.
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NOTICE The extension can be scratched and damaged with a wire brush. Do not use a wire brush on the extension.
- Clean any deposits from the inside of the extension. Use a 6V-7093 Brush with isopropyl alcohol.
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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. |
Expected Result:
The transformer is in good condition.
Results:
- OK - The transformer is in good condition. Proceed to Test Step 3.
- Not OK - An inspection found a problem with the transformer.
Repair: Repair the transformer, when possible. Replace the transformer, if necessary. Be sure to use the correct transformer for the G3500 (A3) Engine.
Reset the control system. Restart the engine. Clear the logged codes.
STOP
Test Step 3. Check the Primary Circuit and the Secondary Circuit
Check the primary circuit and check the secondary circuit according to Systems Operation/Testing and Adjusting, RENR9352, "Ignition Transformer".
Expected Result:
The ignition transformer is within the specifications that are outlined in Systems Operation/Testing and Adjusting, RENR9352, "Ignition Transformer".
Results:
- OK - All of the measurements are correct. Proceed to Test Step 4.
- Not OK - At least one of the measurements is incorrect.
Repair: Place the engine control switch in the OFF/RESET position. Replace the ignition transformer. Be sure to use the correct transformer for the G3500 (A3) Engine.
STOP
Test Step 4. Check the Spark Plug
- Perform the following procedures according to the instructions in the engine's Operation and Maintenance Manual.
- Remove the spark plug from the cylinder head.
- Inspect the spark plug.
- Clean the spark plug.
- Measure the spark plug's resistance after the spark plug has been cleaned.
- Use the 142-5055 Insulation Testing Gp (ELECTRICAL) to measure the resistance of the spark plug. Follow the warnings and instructions that are provided with the tool.
- Connect the red lead of the tester to the terminal post. Because the ground strap is close to the center electrode, you will need to connect a smaller lead to the center electrode. Then connect the black lead of the tester to the smaller lead.
- Use the tester's "20 KΩ" scale.
Note: A standard Ohmmeter cannot be used for measuring the resistance of a used spark plug.
Expected Result:
The spark plug is in good condition.
The resistance is less than 10,000 Ohms.
Results:
- OK - The spark plug is in good condition. The resistance is less than 10,000 Ohms. Proceed to Test Step 5.
- Not OK - The spark plug is not in good condition and/or the resistance is not within the specification.
Repair: Discard the spark plug. Install a new spark plug according to Operation and Maintenance Manual, "Ignition System Spark Plugs - Check/Adjust/Replace - Spark Plugs with Adjustable Electrode Gaps".
Reset the control system. Restart the engine. Clear the logged codes.
STOP
Test Step 5. Operate the Engine
- Install the spark plug according to the instructions in the engine's Operation and Maintenance Manual.
- Install the transformer and the valve cover.
- Reset the control system. Clear any logged diagnostic codes.
- Start the engine and operate the engine in order to generate the diagnostic code again.
Expected Result:
A diagnostic code is not generated.
Results:
- OK - A diagnostic code is not generated. Proceed with normal operation.
STOP
- Not OK - A diagnostic code is generated. Proceed to Test Step 6.
Test Step 6. Isolate the Spark Plug and the Transformer
- Switch the suspect transformer with a transformer from a different cylinder that is known to be good. Install the transformers. Install the valve covers.
- Reset the control system. Clear any logged diagnostic codes.
- Start the engine and operate the engine in order to generate the diagnostic code again.
Expected Result:
The diagnostic code is generated for the suspect transformer.
Results:
- Yes - The diagnostic code is generated for the suspect transformer.
Repair: Make sure that the engine control is in the OFF/RESET position and that the electrical power is removed from the engine. Replace the faulty transformer. Make sure that you use the correct transformer for the G3500 (A3) Engine. Reset the control system. Clear any logged diagnostic codes.
STOP
- No - The diagnostic code is generated for the original cylinder.
Repair: Make sure that the engine control is in the OFF/RESET position and that the electrical power is removed from the engine. Install a new spark plug according to the instructions in Operation and Maintenance Manual, "Ignition System Spark Plugs - Check/Adjust/Replace - Spark Plugs with Adjustable Electrode Gaps". Reset the control system. Clear any logged diagnostic codes.
STOP