So this morning was a bit chilly for us around these parts (weather read 27* fells like 19*) so I go out to get the truck started and let the 3cyl do its job for a bit. I turn the high idle switch to off since I hadn't left it plugged in, WTS goes out and I give it a crank. She starts a bit rough, but only stumbles for a second maybe and fires up. Thinking nothing more, I turn the switch to 3cyl and head back inside. I come back out and notice a CEL on. Truck still is driving fine, although it seems like the truck might have a little less power, but not sure if it was just a combo of the CEL light being on and it being a little icy or what but just a feeling.

Anyways, this is the first CEL I've had since owning this truck so and I figured it'd be a good time to get something to scan the truck myself so I can handle problems and not throw money away at the dealership.

Any inputs on code readers or what may have caused my CEL would be greatly appreciated! Hope everyone's enjoying their thanksgiving weekend!

Alrighty then, safe driving here I come!

OK so update time!

Went for a quick ride to Wal-mart and back, round trip is probably 8 miles. it was 50* outside, no plug in start and my IAT was reading a solid 59*. After driving a bit it settled down in the 90's and I saw a peak of 109 around idle and low speed.

Has my heater gone bad?

Grid heater is cancelled after a period of time or if your speed exceeds 20-25 MPH. The grid heater will remain off.

Grid heater is more obvious when you start up cold and instantly rev the engine to about 1,500 RPM's and hold you can watch the IAT fall quickly and then the ECM will trigger the grid heaters. You'll see the voltage fall rapidly and the IAT will start to rise about 1-2*F at most then grid heaters cycle out again.

It seems like I'm getting all the typical indications that the grid heater is still working. Should I just clear the code and see if it comes back? I'm thinking that starting in MPG mode has caused it to throw this code since it holds IAT at 140 and doesn't fluctuate. Does that sound way out to lunch?

Clear and see what happens. The worst thing that can happen is it will come back. 

Seems like I've had that code before eather when I had many codes pop up when I first ran the high idle kit or when I just needed to clean my battery cables and power going to the grid heater relays. So I would clean and check the battery cables and relays to the grid heaters, clear the codes and see if it comes back.  I don't  now what I was doing wrong when I first got the high idle kit but I got several error codes. But now I just get the ocasional 0500.

On 12/4/2015, 9:28:22, notlimah said:

It seems like I'm getting all the typical indications that the grid heater is still working. Should I just clear the code and see if it comes back? I'm thinking that starting in MPG mode has caused it to throw this code since it holds IAT at 140 and doesn't fluctuate. Does that sound way out to lunch?

According to the error for the P1291 is that the ECm is looking for IAT temperature change in the first 15 second of engine run time, If you locked to 140*F there is no change and the ECM assumes the IAT sensor is acting goofy.

What's weird I've never gotten that code ever in the 4-5 years of having the switch. So its a software difference between the 99 and the 02.

Yea very strange.  

 

So in order to get around this we need to put a note in that you should not flip the switch into any mode until 30 seconds of running?  

 

 

Nick

Yea after reading the full code error I was thinking the same thing Mike. How much difference is there in software between 99-02?

Nick, I'll clear the code and run a little experiment. One leaving the High Idle switch off on every start and then turning it to MPG or any other mode after engines been on 30 seconds. The other will be just leaving it on MPG mode all the time and see if the code comes back and if so, how long it took. I'll keep you guys posted.

So I meant to clear the codes before my drive to work this morning and totally forgot since I was running late. But, on my start up to head back home, the code cleared itself! So, what I'm going to do now is leave it in MPG mode and log every start outside air temp as well as how many starts it takes to throw the code again. Then see how long it takes to go away. I'm really more curious now, I don't think it really matters as far as technical data since the truck seems to correct itself after leaving the switch OFF while starting and waiting 30ish seconds before selecting a mode. Either way I'll keep this post updated.