Tel: (916) 585-6835Mon-Fri 9am - 5pm PST

(916) 585-6835 M-F 9 AM - 5 PM PST

Search Vehicle:

Chevrolet Buick GMC How-To

This is a guide to replace the ignition coils in your GM vehicle with the 4.2L I6 motor. This is a pretty simple procedure. All your really need to do is make sure that any hoses or clamps connected to

This is applicable for the following vehicles:

  • 02-05 Chevrolet Trailblazer 4.2L 6 cyl
  • 02-05 GMC Envoy 4.2L 6 cyl
  • 03-08 Isuzu Ascender 4.2L 6 cyl
  • 02-04 Oldsmobile Bravada 4.2L 6 cyl
  • 05 Saab 9-7X  4.2L 6 cyl


Tools needed:

-Flathead screwdriver (may need a Phillips if clamps have been replaced)

-10mm socket, and extension.

-Small pick (to remove the wiring harness over the #1 cylinder)

-Pliers to remove the clips


1-Remove the clamps on the air intake, and push it out of the way. Be careful not to damage any of the hoses or wires connected to it.

2-Remove the clamps on the throttle body.

2-Remove the 4 10mm bolts that hold the airbox down.

3-Disconnect the vaccum hose on the air box. It's near the front left - lower side of the air box. Remove the air box.

4-Now you can see all 6 coils, but the front coils (#1) is being partially blocked by the wiring harness. Use the pick and pliers to carefully remove the clips that hold this down.

5- Now you can move the wireharness out of the way just enough for you to access the #1 coil.

6- Remove the connectors to the coils coils, and remove the coils with the 10mm socket.

7-Install the new coil, thread the 10mm bolt down by hand first, then tighten. Reconnect the connector, and you're done!


Hope this guide helped. We will soon be making a video.

There are many reasons why this kind of ignition coil can fail. Old ignition coils can fail easily. Humidity, and heat are big killers of these. Other issues can be not as common, but can still happen. I was replacing the alternator on a 2002 Trailblazer a year ago, and I made the rookie mistake of not disconnecting the battery. I arched the ratcehd on the alternator nut. Ouch! No big deal. Put it all back together, and ti started funny. Then it started misfiring consistently, and gave out a P0301 code. Turns out the #1 coil had gave out completely. It never had a single problem until I had arched the ratchet on the alternator. Always be careful when doing other electrical work on your vehicle.