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2004 gmc envoy_sle_xl
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101 Posts
Discussion Starter · #1 ·
Hi all, I've had this random issue with my '04 XL with the I6 for a while now. Truck is running fine, when I pull up to a stop light. or sitting stopped in traffic, it will start idling rough. Some times it shuts off, sometimes it doesn't. If it doesn't shut off, when I step on the gas to go, is goes into "Reduced power mode" and the check engine light comes on, and have no throttle response. To fix the issue, all I need to do is turn off the truck and restart it and all is fine. Happens at random with no other issues. Only coed is "Unclassified ECM Issue".

Any ideas or help would be great.
 

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Premium Member
2004 chevy trailblazer_lt
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3,232 Posts
Hmmm.

OK, here are a couple of things I would check. Fuel injection system pressure. Must be between 50 - 57 psi per factory service manual. The fuel pressure regulator (FPR). Remove the vacuum line and see if gas flows out of either the vacuum line or the FPR nipple. If gasoline flows, it needs to be replaced.

Next time this happens, unplug the electronic fan clutch. If it is going bad, it will set the Check Engine Light and the Reduced Engine Power Light. The electronic fan clutch and the throttle body share the same 5 VDC reference circuit. What happens is the bad fan clutch pulls the 5 VDC reference voltage down to zero and the ECM puts the engine into Reduced Engine Power Mode to keep the engine from overheating. Also check over the electronic fan clutch and throttle body wiring to make sure nothing is grounding out.

Good Luck!
 
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