2nd Gen Non-Engine/Transmission Grid heater ecm input ?

[BarryG]

Reading the manual it states that the grid heaters shut off due to temp (sensor under battery), due to time 180 seconds and by speed going over 23mph. My grids dont shut off over the 23mph speed. When they come on they cycle until the time limit expires. I also have a code showing p0501. I am told the 501 is a vss speed sensor issue (my 01 manual shows 0500 but not the 0501 and have been told it is different issue than the 500). The 01 manual states that the vss (vehicle speed sensor) is no longer used and has been replaced by the rear wheel speed sensor (the one on the top of the rear diff). Well I replaced it and still no change in my 501 code or my grid heaters.



The only other speed sensor I can find in the manual is the one for the transmission. However my speedo is accurate against my GPS. So I am hesitant to just replace it. Havent even checked on the price of it yet.



Does anyone know what speed sensor the ecm uses to trigger the grid heaters? I have read on here in other threads that there is one in the drivers front wheel with the abs system but can find no mention of it in the manual. I have looked darn near everywhere in the manual for it and still no mention.



I know it is not a catastrophic failure but it is darn annoying and I dont really want to lose the heaters nor do I want the sensor whatever it is to just crap out on me somewhere in bfe and cause a bigger issue.



Anyone with any ideas?

 

[jtwcummins]

That code is set when the following conditions aren't met:

ECT above 104*

Map Sensor 5-16 " Vac

Engine rpm between 1400 and 3000 RPM

No VSS signal for 15 secs



I would look at the trans and see if there is a VSS since in transition years you don't really know what you have. My 97 has an engine tagged for a 96 since it was very early in the 97 model run. If there is a VSS in trans remove the plug and check to see if 1 of the pins has 5v EOKO. Try clearing the code with a scanner or disconnect the batts for a few minutes and see if it comes back. If so the best thing to do is clean connectors and check ground. Disconnect batts and remove connectors 1 at a time. Use contact cleaner and diaelctric grease on the plugs before reconnecting. Check grounds on rad support on drivers side and on the fender well for the passenger side. Remove the screws holding the ground lugs, have found many badly corroded. If needed replace the screws and clean to lugs on wires and mounting surface.



Alot of sensors are replaced because of bad connection. The remove reconnect fixes the issue not the new sensor. These connectors live in a very harsh enviorment and get flakey after a few years. I do this first on all ECM vehicles, especially with intermittent problems. Takes time but a big issue is eliminated and you can find broken wires and connectors as you go.

 

[steved]

You have two sensors on your 01... one for 0-25mph (and your ABS) in the rear axle, one for 25+ between the transmission and tcase. My dad's 99 is set up this way also... I believe 97/98 was the change over years.



Now, with the one between the tcase/transmission bad, the ECM will still read (for the speedo) off the rear one based on RPM and input from the rear speedo (this is so you can't disconnect it and not rack up miles on the odo)... but I don't know if that would also allow it to shut things off.



steved

 

[JasonCzerak]

Reading the manual it states that the grid heaters shut off due to temp (sensor under battery), due to time 180 seconds and by speed going over 23mph. My grids dont shut off over the 23mph speed. When they come on they cycle until the time limit expires. I also have a code showing p0501. I am told the 501 is a vss speed sensor issue (my 01 manual shows 0500 but not the 0501 and have been told it is different issue than the 500). The 01 manual states that the vss (vehicle speed sensor) is no longer used and has been replaced by the rear wheel speed sensor (the one on the top of the rear diff). Well I replaced it and still no change in my 501 code or my grid heaters.

Not to tell you how to drive you truck. But why are you even moving the truck while the grid heater is on? why not let her idle to warm up a little bit. it's only 2 minutes and I'm sure your motor will thank you down the line.

 

[BarryG]

Jason:

No problem on the tip. In the morning I start it let it run 45 secs or so then reverse roll down the driveway in neutral, idle up the street (100yds) and then coast down the hill to each of 3 stop signs on a long steep hill. By the time I get to the main road it has been a couple minutes. Letting my truck sit for 2 minutes does not make much difference on the temp. But even more important is the heaters can come on whether the engine is warm or cold depending on the temp of the sensor under the battery. So on cold days if I am just loafing from place to place the heaters come on anyway and the truck is already warm.



All -thanks for the input will check into them

 

[B.G. Smith]

Jason:

But even more important is the heaters can come on whether the engine is warm or cold depending on the temp of the sensor under the battery.

All -thanks for the input will check into them

I believe the temp sensor that causes the grid heaters to turn off is the IAT sensor in the intake manifold. bg

 

[BarryG]

BG:

you may very well be right. I know the IAT does just that measure intake temp but I could swear I read that somewhere that the input for the grids to come on was not the IAT but the battery temp sensor.