Check Engine Light Only Comes on when its cold - Hummer Forums - Enthusiast Forum for Hummer Owners

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Old 02-15-2011, 07:50 PM
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Default Check Engine Light Only Comes on when its cold

So this only happens to me when my truck is left outside over night and it is cold, say 20 or below....

When I start the truck my CEL light comes on and 2 codes are tripped... P0573 Brake switch and P1400 Differential Pressure Low. If I immediately clear the codes and restart the truck, no codes.

Any have any ideas on why the cold may cause this to happen? Dealer say everything checks out.

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Old 02-17-2011, 06:49 PM
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Your PCM goes through phases where it does self testing. So the codes won't come back right away. And those codes are hell too figure out. I see why the dealer didn't tell you the why it is doing that. Especially the brake switch code.

Last edited by luda81; 02-17-2011 at 06:51 PM.
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