My SPA guage boost sensor got over on the intake heater and now its throwing a 0540 code on cold mornings,I checked the 30 amp fuse under the hood for the intake heater and it was fine,do you think it shorted out the heater wire in the intake itself?

Noone one knows?http://www.dieselplace.com/forum/smileys/smiley19.gif Dmaxallitech I thought you would have chimed in by now.

sorry, missed it.


Possible the relay could be bad, next cold morning, check and see with a test light if you have power to the IAH on key up. If not, then I would look at the relay, best to have a scanner and see what the feedback voltage is.

Where is the relay located,if it's bad do you have some of them?

the relay mounts on the drivers valve cover back by the firewall, I dont have any, it must be replaced as the whole block assembly, and goes for about 100 bucks. It is covered by the 100k warranty but when you figure your 100 dedect, dont make sense if you can do it yourself.

Ok thanks dmaxallitech,I done a search and another post ahile back mention 2 fuses,1 mega fuse. Where is the mega fuse located,that may be the problem. I hope.

The MEGA fuse is located under the fuse block cover, not the panel that is easy to remove, the large plastic close out piece. its mounted just fore of the fuse panel under the hood. Remove the plastic close out and its righ there, has a stud/nut on each side, easy test is to use test light on both sides of it, if power, great, if not, replace. Usually when this goes though, it will also trigger a a P0380 code for glowplugs as this powers both. Even easier way to test this fuse is to check for power at the heavy cable going to the relay block on the valve cover, its covered with a insulating grommet similer to whats on the alternator nut. Just hit your teslight on that, if powered, your circuit is good up to that point. Only thing left really is IAH itself or the relay.

2001 dmax with 0540 code in it.....replaced the relay, it wont even start and run now, this was the only code in it. What voltage is the iah supposed to have, my snap-on scanner shows 4.8 volts regardless of whether the iah is on or off, if i test the stud by the heater itself i can get 12 volts....any suggestions or am i just stupid and missing something?http://www.dieselplace.com/forum/smileys/smiley5.gif

should mention that after the relay was replaced......truck ran fine for 2 days, cold morning it started and ran for about 15 secs and died, hasnt started since, low pressure fuel pump is working, and only code it will set is the 540, which i can clear and upon cycling the switch to attempt a start will recur. No one i have talked to has a clue and said a 540 code shouldnt (in theory) keep it from starting

ok thanks eric.... another question for ya,at what temp does the IAH come on at,havent gotten the chance to check with my test light yet but this morning it didnt throw the code but it was like 67 deg. outside temp.

Just wanted to let the few people that may be interested......I found the problem, fixed it, and now it runs fine and doesnt throw a 540. No one seemed to know anything or wanted to help, here or anywhere else, so I just started going thru every piece and wire myself and found it.

Im still waiting myself for a cool morning cause im not sure if it's supposed to be hot on the fuse block all the time. what cha' think eric?

I have both the P040 and the P0380 as well. There is power to the big stud on the relay, but when I key it up cold, there is power to only one of the studs going out. According to Helms, there should be only one out for the glow plugs, and a smaller one out for the IAH, yet mine has two heavy ones. Also, Helms shows heavy light blue (I believe) wire for the plugs and lighter tan for the IAH. Each post has a a light blue on it, and the one with the tanis on the one that shows no power. I am trying to avoid letting the dealer tackle this, as am told that the plugs not under warranty.


Thanks for any help you might give me.

Im still getting the 0540 code not sure what temp that the IAH turns on