Over the past couple weeks when I start up during a cold morning I'd happen to get the occasional P1291 code for the lack of intake heat.  I'd clear the code and then it wouldn't happen again for a few days or so, depending on how many times I drove the truck.  Strange part is when it would throw the code, I'd immediately shut down, check with a reader, clear the code, and start up again.  All would be fine.  I thought maybe I have a bad or sticky relay that just happened free up, so I checked around to see who has them.  Thankfully they're readily available but they're not cheap either.

Before I went and spent the money I thought I'd do a full diagnostic just to be sure.....  I checked the small orange and yellow wires for continuity.  I checked all the large cables at the solenoid and to the grids and the battery.  The only connections that gave me reason for doubt was the small orange and yellow wires which were a tad loose.  Their push on springy fitting had the slightest amount of movement in them on the stud as if the springy connector wasn't as tight as it could be.  I wiggled them around and tried to smash the spring tighter with my fingers.  Not a lot of room down there.....

Then I started the engine and checked everything as the grids cycled.  For those who dont already know, both of the grids initially heat up when the WTS light is on and then they alternate as they cycle when the engines idling.  Meaning as the engine idles they both dont heat up at the same time but only one grid heats up while the other is off, and they trade during the next cycle.

Nonetheless, everything seemingly works and the code wasnt thrown when performing the diagnostics.

So my question is, has anyone found that their grid heater relays were sticky or worked randomly?  I dont live in an area where road salts are used and there is ZERO corrosion on this truck and everything is clean and tight.

Might have to monitor your IAT sensor reading...

 

I was thinking that too and will certainly check if I get the code again.  I actually have a spare IAT sitting around I picked up for some reason I cant remember.....

But that said, I can pull up the IAT readings on my scanner at the time of the code and the IAT temps were normal with the ambient temps so I'm only guessing at this point that the IAT was reading correctly and the grids weren't generating any heat from a possibly loose connection.  I'll have to wait and see.....

You'll have to watch it closely during the initial start. The IAT temps only shift maybe 2-3 degrees up and down typically. As the monitor and set conditions state...

Temperature rise from intake air heaters is monitored for first 15 seconds of engine operation. DTC may be stored if initial Intake Air Temperature (IAT) sensor reading is 0-66°F (-17.8 to 18.8°C), Battery Temperature Sensor (BTS) and IAT sensor are within 10°F of each other, time between end of preheat and engine run state is less than 30 seconds, engine is cranked for less than 5 seconds before engine starts, preheat is completed before engine starts, post-heat is active and no IAT sensor or intake air heater relay DTCs exist.

So is it possible your battery temp sensor is damaged or connector is damaged?

One of the reason I'm quick to grab the OBDII error code links because the monitor and set conditions are typically listed first thing on the error code. So now at least you have something to look for and why its setting the code.

Which might now go back to why the battery life was shorter if the battery temp sensor was damaged it might of been charging at the wrong rate causing the battery issues. At the same time now creating the P1291 code. Weird how this might all be connected...

Well bummer.....  It did it again today.  Ambient was about 55* and the overhead said 59* because its parked in the garage.

What I "thought" happened this time was the grids cycled while the wait to start light was illuminated.  Then I started the engine and after about 5 seconds the check engine lights up.....code thrown.  What I'm not sure about is why the data says the IAT was reading 71.6*.  What cha think?

Sound like a mismatch between the IAT and Battery Temp sensor. Might try the extra IAT you said you had.

I'll give it a try.....

Beyond that you might check the battery temp sensor under the driver battery.

Curious as to why you would think the battery temp sensor?  I dont have a charging issue.  I've checked.....  Would the battery temp sensor determine whether or not the grids cycle?

Again read the monitor and set condition...

Temperature rise from intake air heaters is monitored for first 15 seconds of engine operation. DTC may be stored if initial Intake Air Temperature (IAT) sensor reading is 0-66°F (-17.8 to 18.8°C), Battery Temperature Sensor (BTS) and IAT sensor are within 10°F of each other, time between end of preheat and engine run state is less than 30 seconds, engine is cranked for less than 5 seconds before engine starts, preheat is completed before engine starts, post-heat is active and no IAT sensor or intake air heater relay DTCs exist.

My scanner isnt that in depth so I'll be changing the IAT first, then the battery temp sensor, then I guess the relays.....

Do you happen to have the ohms numbers for the BTS?  I bought one and am checking the resistance of the new one, the old one, and the old IAT.

Currently the old IAT and the new BTS both read 16.65 and the old BTS reads 17.31 at 20k in the meter.

Let the stabilize in the room temperature for at least an hour. Best to have them both suspended and not being touch by your hands or picking up your body heat. Another way is to place them both in a glass of ice water and test for matching ohms.

As for BTS I don't have any information. Sorry.

 

 

Edited March 9, 20169 yr by Mopar1973Man

Ok.  They've all been sitting in the garage for over an hour and it's 55* in here.

                                     Testing a BTS  99 Dodge Ram

                      https://www.youtube.com/watch?v=KIuWfd_2LmY

Thank you.

An update.....  I left all three sensors laying in the garage and this morning they all read the same.  So that said, I chose to leave the old BTS in since they're about $40 each and its seemingly reading the same as the new one.  But because of how its throwing the code, it seemed more like a sticky solenoid in the relay so I swapped it out for a new one just to rule that out.  I hate throwing parts at things but there isnt much I can do at this point.  Well unfortunately the new relay didnt help since it threw the code again.  Now I'm thinking that I have a faulty grid element.  When I cycle the key, I'm getting power to the elements but the housing isnt warm.  I checked the resistance and got some odd numbers.  I dont care for my meter.....

I ohm checked my battery temp sensor as well as my grid heaters.  The ambient air temp was 68° F.  the BTS was 11,830Ω with one of my meters and 11,930Ω with another (harbor freight free-be).  The grid heaters were checked by ohm testing from the positive post of one heater at a time to the common ground.  the readings I recorded were 36Ω for the + post closest to the valve cover and 26Ω for the other one. 

Katoom Had the same thing going on with mine. After checking grounds, Batteries and anything else I could think of, with no good results I pulled all wiring from batteries to relays to grid heaters. Found a little corrosion on the connections to the grid heaters. Cleaned all connections and have had 0 trouble since. Also while the squeezed the orange and yellow wires connectors to make better connect.  

Found it.....
The ground cable from the grid element to the manifold had a bad connection and was causing an intermittent ground issue.

Here's what I found.  Because I dont think I could have found this little cable anywhere local and the corrosion was on the exposed end, I shortened it and re-crimped it and sealed it.