frank@fpexton.com

Excellent! Did you get the sensor out from the rear or did you go through the hole in bedroom?

Bill, The 41 and 31 pins are on the oem side of the ecm, not the Cummins side. So the wiring diagrams in Quickserve are only for the Cummins side and I can't tell which temp sensor the ecm uses to signal the grid heaters on. Should be the intake air temperature which I think is the one in jacwjames' first picture. It should be in the cavity right below the grid heaters, which is the intake. I think that part number that James gave you is right too. Like they said if you're showing a code when it is disconnected then I think your wires and connections are fine, the sensor isn't sending a temperature to ecm. I'd try to buy one through a Cummins dealer or truck dealership and if they have it in stock, they might let you change it out and see if it fixes the problem. You're right the air pressure doesn't have anything to do with the grid htrs. Frank

Here is a general information file on the cold start aid. The graph shows intake and coolant temperatures sensor averages. That's why I am thinking maybe the intake temperature sensor is the one. 010-029 Cold Start.docx

After looking on Quickserve, it might be the "Intake Manifold Temperature sensor" that controls the "Cold Start Aid Circuit". I've attached a Quickserve 019-164 procedure that shows how to check the wires. Looks like 3408346 is the right part number. Cold Start Aid.pdf

I have a 2000 Windsor with the grid heaters and live in WY. I've had it for 10 yrs and the "Wait to start" light has never come on, but I've never had any trouble starting it until last year and now no matter what the temperature is, cold or hot it it spits and sputters and completely engulfs the coach in white smoke. So I'm interested in this subject. I haven't taken the time to figure out why the grid heaters aren't working. The ambient air sensor on my truck "Cummins ISX" just hangs on the harness, but it is a 2010. Also a Barometric pressure sensor senses your barometric pressure (altitude)and keeps your engine running right whether you are at sea level or the top of a mountain.. That last picture you posted Bill looks like a barometric pressure sensor. There should be a part number on it if you can get it out. I know with my trucks , if you take it to the shop, they don't bother to test them, (all sensors) they just tell you to change them out. Easy for them to say that when it's not their $250. You could probably check continuity of your wires to the relay to see if that's the right sensor.