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Duramax 6600 Discussion Forum for the Duramax 6600 Diesel Engine, including the LB7, LLY, LBZ & LMM engine specific topics.

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Old 11-11-2005, 07:23 PM
Troy Troy is offline
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The SES light came on last week. Code that was set is P0540 (Intake Air (IA) Heater Feedback Circuit). I have reasearched this failure and determined that the most likly cause is the IAH Relay. Has anyone replaced this relay? Where is it located? Can I replace this relay myself?

Thanks for the help.

2002 GMC CC 2500HD, 6.6LTD
Stock

[ 11-12-2005, 06:25 PM: Message edited by: Troy ]
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Old 11-13-2005, 05:58 PM
Troy Troy is offline
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Anyone know how to locate this relay?
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Old 11-13-2005, 08:18 PM
DmaxMaverick DmaxMaverick is offline
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The relay is just forward of the glow plug relay/controller, on the left (driver's side), above the valve cover near the rear. Look at the intake manifold pipe where the heater is (it will be a hexed plug with a stud/nut/wire on it, about 1-1/4" dia.), and follow the wire to the relay. On mine, it appears to be a no-brainer, and pretty simple. The manual specifies the only difference between CA and non-CA models is the CA model is part of the glow plug circuit, and the Federal model is independent.
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Old 11-14-2005, 10:12 AM
OC_DMAX
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I went camping for a week in the CA Sierra mountains a couple of weeks ago. The temps were 20 def F in the morning. The SES came on and a P540 code has been set. Looks like the cool temps (at least by SoCal standards) kept the IAH on too long and something gave way. So we have similar problems.

When viewing the engine from the drivers side fender, the IAH relay is located behind and slightly to the left the two 50+ pin large electrical connectors that the Edge Juice would hook in to. It is above the drivers valve cover, about mid engine.
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Old 11-14-2005, 12:15 PM
Kennedy
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FWIW, I get the same code on my 2002 when it's cool (about 65
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Old 11-14-2005, 07:08 PM
Troy Troy is offline
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Thanks for the info. I first noticed this code back in July up in the White Mountains (temp ~55 deg) in the mornings. After I reset the code it didn't set again until the last couple weeks. It just started setting again since it turned cool by Tucson, AZ standards ~ 50 deg in the early AM. I will check for a short and have ordered the relay (on back order at the local dealer). We have a trip planned up to the mountains next week and I'm concerned about starting without the Intake heater working. I will let you know what I find out.
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Old 11-15-2005, 05:08 AM
Kennedy
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It shouldn't give you any grief. They start quite well as the glow plug is the primary influence. Have you ohmed the coil to make sure it's not the heater itself? The realy seems to be primary issue, but you never know...
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Old 11-15-2005, 08:06 AM
OC_DMAX
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Troy - The truck will start just fine without the IAH. My truck was starting in 20 deg F morning temperatures in the Sierra Mountains a couple of weeks ago. I kind of wonder if this IAH is more of an emission thing. I need to get the truck to the dealer after our Thanksgiving camping trip to get it fixed.
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Old 11-16-2005, 07:57 PM
Troy Troy is offline
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Thanks for the info.

I replaced the relay last night. I think it takes 2 warm-up cycles before the SES light is turned on so I will find out tomorrow morning if it fixed the problem. I checked the heating element and it appeares to be fine. Also no shorts in the IAH power feed.
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