DTC P0542; Intake air heater "A" circuit high.

[JFK]

My truck is still covered in snow or I'd go take a pic and post it.
I'm sure someone else on here has a pic or could take and post one for you.
Here is a pic of the solenoid by itself...
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I THANK everyone for their help. The photos helped a lot. I've disconnected the positive battery cable to the solenoid, I noticed it has a "fusible" link and I'm guessing the "link" would've melted before serious damage to the grid heater occurred. One additional point, I noticed the (on board) truck volt meter is indicating 14.5 v while the engine is running, which would indicate the heater is off. I'm now wondering if the problem setting off the "code" is intermittent?

 

[DavidC]

Never assume a safety device will work. Most times it probably will but there may be cases where it doesn't.

 

[kthaxton]

I THANK everyone for their help. The photos helped a lot. I've disconnected the positive battery cable to the solenoid, I noticed it has a "fusible" link and I'm guessing the "link" would've melted before serious damage to the grid heater occurred. One additional point, I noticed the (on board) truck volt meter is indicating 14.5 v while the engine is running, which would indicate the heater is off. I'm now wondering if the problem setting off the "code" is intermittent?

Be sure to occasionally do the wiggle test the others had suggested. The fusible link will not prevent the bolt melting issue.

While I have not laid eyes on a failed grid heater bolt myself, I frequently hear the term "arcing" used to describe what happens with the bolt (in which case, I'm fairly certain the f-link would protect this), but I am thinking arcing is not the issue. To me, it appears to be a resistance issue. While I do not know what would create resistance initially (bolt not tight enough? contamination?), once it starts, it is a snowball affect.

In circuits with high amperage, used continuously (sort of continuously in this case) a small amount of resistance will create heat. More heat creates more resistance, then more heat etc etc. It looks to me as if this heat eventually melts the bolt. It's called "thermal runaway". In this case, there is no overcurrent situation (like a direct short) therefore it would never blow the f-link.

This is why in circuits with high current use, for long(ish) periods, have fusible links instead of fuses. Often times, if a fuse it put in an f-links place, the fuse or any soldered terminals can melt, all while the fuse never blows.

 

[Ltngdrvr]

I THANK everyone for their help. The photos helped a lot. I've disconnected the positive battery cable to the solenoid, I noticed it has a "fusible" link and I'm guessing the "link" would've melted before serious damage to the grid heater occurred. One additional point, I noticed the (on board) truck volt meter is indicating 14.5 v while the engine is running, which would indicate the heater is off. I'm now wondering if the problem setting off the "code" is intermittent?

Sure, the code sets when the fault has occurred for a long enough period or more than once, and the fault can stop occurring but the code is set in the ecm.
Now, with the grid heater disconnected, you will probably get another code set because of that.

 

[sag2]

P0542 sets after the monitor fails in two drive cycles, and turns off after four good drive cycles. Mine set last week coming home from a 500 mile trip, and has not reset since I got home and cleared the code. I went in with an inspection camera and the nut looks to be OK, it is somewhat hidden from the camera because I can't bend it after it goes in past the grid heater. Stud is tight. I wired in an LED on the solenoid stud feeding the grid heater so I can monitor if the solenoid sticks on. Just going to watch it for a while and see if it sets again.

 

[gsbrockman]

I wired in an LED on the solenoid stud feeding the grid heater so I can monitor if the solenoid sticks on. Just going to watch it for a while and see if it sets again.

I like this a lot..........