ELEMENT 4N0490 - Caterpillar

Ignition Transformer
If an ignition transformer is suspect, use the following procedure to check the transformer:
Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring.Do not attempt to remove the transformers when the engine is operating. Personal injury or death may result and the ignition system will be damaged if the transformers are removed during engine operation.
Ensure power to the engine OFF.
Illustration 1 g02850759
(1) Wire seal
(2) Lockwire
(3) Ignition harness
(4) Transformer
(5) Terminal for the spark plug extension
(6) Extension
(7) Terminal for the spark plug
(8) Spark plug
(9) Mounting flange for the transformer
Remove wire seal (1) and lockwire (2).
Disconnect ignition harness (3) from transformer (4). Remove the transformer and extension (6) as a unit.
Inspect the body of the transformer and of the extension for corrosion and/or for damage.
Inspect the O-ring seal inside the spark plug end of the extension for damage. If the O-ring seal is cracked or hard, install a new O-ring seal.
Inspect terminal (7) inside the extension for looseness, for corrosion, and/or for damage. Insert an extra spark plug into the transformer and check for spring pressure of the terminal.
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.
Illustration 2 g00754013
Symbol for a diode
Measure the voltage of the diode for the primary circuit.
Illustration 3 g00829100
Transformer connector for the ignition harness
(A) Positive
(B) Negative
(C) Unused
Set the multimeter to the diode scale. Measure the voltage between pin "A" and pin "B" on the transformer connector for the ignition harness. The polarity is not important.
Reverse the polarity of the probe and measure the voltage between the pins again. For the diode of the primary circuit, the correct voltage between pin "A" and pin "B" is approximately 0.4 to 0.6 VDC. When the polarity is reversed, there is no reading.Voltage that is significantly outside of this range could indicate a problem with the transformer.
Measure the resistance of the secondary circuit.
Set the multimeter to the 40,000 Ohm scale. Measure the resistance between terminal (7) for the spark plug and mounting flange (9) for the transformer. If the extension is removed, the resistance can also be measured between terminal (5) and the mounting flange. Resistance that is significantly outside of this range could indicate a problem with the transformer or with the extension.
Switch the suspect transformer with a transformer from a different cylinder that is known to be good. Install the transformers.
Reset the control system. Clear any logged diagnostic codes.
Start the engine and operate the engine in order to generate a diagnostic code. If the problem follows the transformer, replace the transformer. Make sure that you use the correct transformer for the engine. Reset the control system. Clear any logged diagnostic codes.If the problem stays with the cylinder, there is a problem with the spark plug or with the electrical circuit for the transformer.For instructions on inspection and replacement of the spark plug, refer to the engine Operation and Maintenance Manual.For