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C5500 duramax 6.6L guru mechanics needed

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BamBam

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having some issues with fuel system and transmission not slowing truck when going downhill, also at stops must hold break because truck pushing forward. Hoping I'll be able to talk to someone to explain my problem more over the phone...?
Thanks!
 
my dad has asked me to post this for him as he's not a computer guy
Anyways, he is having the code P0500 come up and has previously replaced the speed sensor a few times I believe. The service truck mainly goes in to limp mode if he is driving through wet conditions. What caused the issue today was that he decided to wash his truck..... And had to drive home at 10 mph...not a happy camper. Are there any tests he could run on the wiring harness? It all appears to be in good condition. And where would the PCM be located, also any tests that can be done.
Many thanks in advance!
 
update: replaced fuel pressure relieve valve, fuel system working good
Now getting code P0500.... Speed sensor has been replaced a few times. Truck mainly goes into limp mode if driving through wet conditions.. Or like today, decided to wash truck...
Any tests that can be done to wiring harness? Location of PCM and any troubleshooting..
THANKS,
 
Wished I could help you out, but I'm just not that familiar with the MD trucks and where everything is at. I do know P0500 is for the output speed sensor signal not matching the wheel speed sensor reading. If the vehicle is going into limp mode, that means the TCM is the one setting it and you most likely also have a P0700 with it. I'm pretty sure on these, the TCM reads the output speed sensor, and then the TCM sends the signal to the ECM. So you most likely need to be looking at the TCM and it's wiring.
 
He said I shouldn't have called it limp mode, because it doesn't shift out of first gear and transmission light comes on. Can clear with scan tool but comes back right away.
Thanks!
 
From what I can find, it says teh ECM and TCM are bolted together in a stack on the passenger side firewall. The TCM will have 2 plugs going to it, and an LLY ECM will have 3.
 
Respectfully this mess needs to go to a local shop where you can rent some experience to figure this out. It will save you and your dad time and similar breakdowns from the same cause as quite frankly your posts do not have enough info to get anywhere with it.
 
Great thanks! He found it, cleaned the connections and checked the wires to no avail..
 
I just checked ALLDATA for info on the circuit for an 01(thats what I have), and you need to check it for ANY other codes. Most scanners(including those at the parts stores) CANNOT read TCM codes, you need a high end scanner to read TCM codes. Without checking for TCM codes, this is going to get REALLY expensive to try and fix. You need to particularly look for a P0721 or P0722.
 
I pulled up the sensor specs. If this is a 2 wheel drive truck, then the resistance of the output speed sensor should be 2600-3160 OHMS. Check it at the sensor 1st and see if it is correct, if it is, go to the TCM and pull the C2 red connector. Pins 15 and 16 are for the output speed sensor. With the speed sensor hooked up, measure resistance and verify it is within the 2600-3160 OHM range. If it is more than a few ohms different than the reading at the speed sensor itself, this points to a wiring problem.
 
I wonder if it is a bad NSBU switch? I think this was one years of the bad switches. I know there is a newer switch that took care of some issues with wet and limp mode. The bad NSBU could be causing other issues as well.
Were there any modifications done to this vehicle or is it stock? Different tire sizes could also cause some issues with the speed sensors.
 
The truck is stock, same tire size. The switch has never been replaced, will tell him to check, Thx!
 
Any other codes showing?
The NSBU switches that have issues are the black ones. The newer switches are tan.
You may also want to check the wires leading to the VSS to make sure they are not broken or frayed.
 
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The bad NSBU was used from 01-sometime in 03. It was mid year 03 they switched to the single plug switch(the bad ones were black with 2 plugs). And when they failed it caused a no gear situation, or 3rd and reverse only with a range shift inhibited message in the gear display or it would flash. And they never caused a P0500 code to pop as that code is caused by the ECM not seeing the replicated speed sensor signal from the TCM, or the speed sensor signal it is receiving does not match up to what teh ABS is reading.
 
BamBam said:
Thank you so much! Would this be the same for 4 wheel drive?
Click to expand...
Similiar, but 4X4 uses a different resistance for the output speed sensor mounted in the transfer case. The numbers I have for a 4X4 are 1420-2140 ohms for the output speed sensor.
 
Your right Ferman, but it is still worth a check, as a few of the newer switches have failed. We need some more info here to zero in on the possible causes. I would also clear the codes and see if they come right back, or if they take time to reappear.
 
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