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cumminspower

Bad IAT Sensor?

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Lately I've been wondering if possibly I've got a problem with my IAT sensor. I haven't gotten any codes but my grid heaters cycle at weird times & I also seem to be getting pretty bad gas mileage. 13-14mpg in town...Sometimes after I drive the truck for a while & it gets up to normal op. tmps I can shut it down, wait 5 minutes, start it back up & my grid heaters start cycling again....Shouldn't the intake manifold have already gotten warm enough that it wouldn't need to cycle the grid heaters again? I live in Alabama too, so it's not like it's cold or anything.... I've already pulled the IAT sensor out & checked it & cleaned it....It wasn't even dirty at all.....I'm just wondering if it might have a problem....Is it very common for one to have a problem & the truck not throw any codes at all?

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Only way to be sure is to get a Live Data tool and see what the value is. Check both the Engine Coolant and IAT Sensor. From a cold start both sensor should be the same. Then at full running temp the IAT should be about +40*F over outside air temp.

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Only way to be sure is to get a Live Data tool and see what the value is. Check both the Engine Coolant and IAT Sensor. From a cold start both sensor should be the same. Then at full running temp the IAT should be about +40*F over outside air temp.

Thanks. I appreciate the information. I will see if I can get it checked & make sure there isn't a problem.

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My grid heaters don't turn on even on a "cold" start at this time of year, and never on a repeat start. Definately something to look into. You say you don't have codes but have you had any codes but have you had them read by a coder reader, not just the key trick? I got nothing on the key but had 4 codes when the truck shut off. Apparently not all the codes show up in the odometer window. Yes, warm up mode sucks the fuel & low performance... which is why we're studying making IAT foolers.Russ

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I don't know about the 2nd gen owners manual, but the 3rd gen owners manual details the temps/specs for when the grid heaters should operated. On a 3rd gen it's anytime the intake manifold temps are below 66*, I have heard, but never verified, 50* for a 2nd gen.

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To add to Russ comments there... Yes the IAT sensor controls the initial use of the grid heaters before starting but after the engine is running it seems the Engine Coolant Sensor controls the post grid heater usage. I been running all winter with mine locked at 140*F and there is no grid heaters at key ON but after you start the grid heater cycle in and out. But now with warm weather I never see grid heaters any longer. So yes its possible for a intake temperature sensor (IAT) to fail within normal run specs and not throw a code but also be far off the mark from actual manifold temp. So this why I suggest using a live data tool to check the sensor value. Because like my setup I'm locked at set temp now no codes no issues. But now if the data tool can't be had you can just replace the sensor as a guess. They seem pretty cheap for $22 buck for a IAT sensor...

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Just a thought... What are your actual engine temperatures? What if the sensors are right but the thermostat is stuck open? That would make the engine run cold. I don't know if it would be enough to cause the grid heaters to run.

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