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Why does 2004 Hummer H2 have reduced engine power?

Why does 2004 Hummer H2...

Why does 2004 Hummer H2 have reduced engine power?

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Answered in 2 minutes by:
1/19/2012
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29,662
Experience: GM Grand Master Technician 2007. 14 year experience.
Verified

Often this is a ground wire at the back of the drivers side cylinder head. This ground attaches at the same spot as the braided ground strap. Try pulling the black wire to see if it gives. If so then replace the terminal end.

IF not then look to bad wiring at the throttle body. These are also common for bad wiring at the plug or near it so checking the plug and wires there may find the issue. If these don't work then can you get the codes from the system?

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Customer reply replied 6 years ago

My 2004 Hummer was working 100% fine before installing a Hummer/GM certified off road light kit, made specifically for this vehicle. The only things touched was the ground mounting spot and the trailer brake harness under the fuse box under the hood. I started the vehicle and after 10 seconds it bogs down and says reduced engine power.

I then disconnected the harness for the off road lights completely, undoing the ground harness and reattaching the trailer brake connection just like it was before I started and it still shows this reduced engine power condition. If I put the Hummer in reverse, the engine dies instantly. I know its something that I've done, but I went back and forth over my steps 100 times in the last 3 hours, I'm clueless.

Ok, check the connectors under the dash for the pedal. Take them off, clean then and put then back on. If that does not then can you get me a code number?

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Customer reply replied 6 years ago

Nothing was done inside the vehicle at all, this was all under the hood work!

I have no way of moving the vehicle now at all.

Ok, if all the grounds are good then try a reset. Keep the battery cables off, touch the ends together for 10 seconds then put them on the battery to reset the vehicle.

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Customer reply replied 6 years ago

Did the battery disconnect and re-cleaned my ground, still nothing, just goes to reduced engine power after a couple seconds of starting.

Ok where exactly was the ground which is touched?

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Customer reply replied 6 years ago

The ground has a couple more wires attached to it already, on the frame in front of the driver front wheel.

Ok, can you take them off and clean to bare metal. Second take the grounds under the drivers door off and clean them.

Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29,662
Experience: GM Grand Master Technician 2007. 14 year experience.
Verified
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Customer reply replied 6 years ago

I have fixed it. It wasn't a ground issue at all. Under the hood in front of the driver area at the fuse box there. The problem was when I put the surrounding cover back on, I was pinching some wires off. When I started the hummer without the cover fastened it ran fine, once I put the cover back on a second time. It coded again. So I took the cover back off and it was fine once again.

So I put the cover on very very carefully (taking like 10 minutes), making sure all grooves and fasteners were hit 100% correctly and it ran fine. I took it on a*****around the neighborhood area and at times opening up the throttle, and no problems whatsoever! So my problem was simply that cover pinching stuff off.

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Gm Tech (Cam)
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29,662
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Experience: GM Grand Master Technician 2007. 14 year experience.

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