How to Check a 1998 GMC Ignition Coil

by Christian Killian
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Testing the ignition coil on your 1998 GMC truck will tell you right away if the coil is faulty. Learning the procedure for testing the coil can save time and money. The coil on the GMC looks a little different from the older cylindrical coils that previously sat on these engines, though the function is the same. You will need a digital multimeter to test the coil; if you don't have one they are available at home centers and auto parts stores.

Step 1

Disconnect the negative battery cable from the battery after loosening the retaining bolt on the cable end with a wrench. Isolate the cable from the battery, which eliminates any chance of the ignition becoming energized while you are working on it.

Step 2

Locate the ignition coil on the driver's side of the engine just above the valve cover and bolted to the intake manifold. Remove the large wire coming from the top of the coil. This is the high-tension connection and you can set the wire aside for now.

Step 3

Locate the wiring harness connector on the top of the coil. Release the retaining clip on the connector then pull it straight off the coil.

Step 4

Set your digital multimeter to the ohms setting and place one probe on the negative terminal inside the connector on the coil. Which probe you place on which terminal is not important, you are measuring resistance, rather than amps or volts. It will be marked on the plastic case to indicate positive and negative. Place the other probe on the positive terminal. Note the reading on the meter. A reading of zero indicates a broken wire in the coil winding and it needs to be replaced. The resistance on this test should read between .7 and 1.7 ohms. Anything outside of that range indicates a bad coil.

Step 5

Remove the probe from the positive terminal and place it on the high-tension terminal while leaving the other probe on the negative terminal. Note the reading on the meter; you are looking for a reading between .7 and 1.7 ohms (your meter may display 7,500 and 10,500 ohms). Again, anything outside this range indicates a bad coil and a reading of zero indicates a broken winding. Replace the coil in either case.

Step 6

Reconnect the wiring harness connector and the high-tension wire to the coil. Install the negative battery cable on the battery and tighten the retaining bolt with a wrench. If the coil tests faulty, source a new one from the dealership or an auto parts store and replace it.

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