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2012 LML 6.6L Turbo Diesel 3500HD4x4 Crew 297K
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Discussion Starter · #1 ·
I bought this truck and things quickly went downhill about 3 months later. On the highway the engine sputtered and shut down. This began the never ending bullshit. My traction control and abs light came on and are always on. the DIC flashes service stabilitrak, trailer brake control, traction control with no CEL and i really need my trailer brake control to work as i haul big trailers frequently. My brake lights stay illuminated when the headlights are on. I ended up paying $8,500 for the entire fuel system to be replaced and or cleaned from tank to injectors, which fixed that problem. The mechanic had lifted the cab and bed off the frame to do this. Shortly after this I started leaking oil and power steering fluid. I changed the trailer brake control relay, brake pedal position sensor and the trailer brake control switch to no avail. I recently brought it to the dealership thinking, "Hey GM mechanics, GM truck, they'll know what's up". boy was i fucking wrong. $450 just to diagnose and start working. they told me i had an oil pan leak, front hubs were "about to fall off" , that this is the cause of the DIC warnings, i got an oil change and a few keys made, final total was $1,350. It was not an oil pan gasket leak, it was an o ring leak in one of the engine oil cooler lines which they found out when i brought it back to them and took care of but i still have a few drips of oil every time I park after driving and notice my oil pump makes a vibration humming noise and wondering if they put the incorrect oil in it. I changed the front hubs and this had done nothing. I changed the master cylinder and it still leaks intermittently. I did some research and found that incorrect brake light bulbs could cause the brake lights to stay on but the same bulbs were in place as when i bought it and it never had any issue up until the fuel pump shredding gears on the highway. I did put aftermarket LED brake light bulbs in and all that changed was the rate at which my turn signals blink, which is much faster now. any help would be MUCH appreciated because i lost trust in my local Chevy dealership and i am skeptical that the mechanic hooked everything up right when reattaching the cab to frame. I'm just lost and could use some guidance. $13,000 for the truck and i am about $12,000 in in repairs already
 

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Was the bpp sensor calibration completed in the bcm and ecm after it was replaced?
What does bpp sensor data show in the bcm and ecm?
Shorted wire somewhere?
Internal short in the bcm?
Internal short in the tbcm?
 

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2014 WT LML, 211k, LDS 64mm, CTS2, SD cold air intake
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51 Posts
Was the bpp sensor calibration completed in the bcm and ecm after it was replaced?
What does bpp sensor data show in the bcm and ecm?
Shorted wire somewhere?
Internal short in the bcm?
Internal short in the tbcm?
Has your fuse box on the drivers side fender ever been pulled?

Reason I ask is that I pulled mine to add fog lights and a new bumper. After I did this I noticed my passenger side rear running light and right side license plate light would work intermittently. If I wiggled the fuse box, it would work which told me I didn’t have the upper portion properly seated and locked down.

Also I pulled the 40 amp fuse to disable the traction control because I hate it. This fuse is associated with all the idiot lights you listed and all are lit on my dash as well. I cant remember what number it is but it’s shown in the manual.

It really sounds like you’re having a low voltage issue. As for the brake lights, I’d definitely check the wiring in the aftermarket light or put your stock ones back in to see if the issue persists.
 

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I bought this truck and things quickly went downhill about 3 months later. On the highway the engine sputtered and shut down. This began the never ending bullshit. My traction control and abs light came on and are always on. the DIC flashes service stabilitrak, trailer brake control, traction control with no CEL and i really need my trailer brake control to work as i haul big trailers frequently. My brake lights stay illuminated when the headlights are on. I ended up paying $8,500 for the entire fuel system to be replaced and or cleaned from tank to injectors, which fixed that problem. The mechanic had lifted the cab and bed off the frame to do this. Shortly after this I started leaking oil and power steering fluid. I changed the trailer brake control relay, brake pedal position sensor and the trailer brake control switch to no avail. I recently brought it to the dealership thinking, "Hey GM mechanics, GM truck, they'll know what's up". boy was i fucking wrong. $450 just to diagnose and start working. they told me i had an oil pan leak, front hubs were "about to fall off" , that this is the cause of the DIC warnings, i got an oil change and a few keys made, final total was $1,350. It was not an oil pan gasket leak, it was an o ring leak in one of the engine oil cooler lines which they found out when i brought it back to them and took care of but i still have a few drips of oil every time I park after driving and notice my oil pump makes a vibration humming noise and wondering if they put the incorrect oil in it. I changed the front hubs and this had done nothing. I changed the master cylinder and it still leaks intermittently. I did some research and found that incorrect brake light bulbs could cause the brake lights to stay on but the same bulbs were in place as when i bought it and it never had any issue up until the fuel pump shredding gears on the highway. I did put aftermarket LED brake light bulbs in and all that changed was the rate at which my turn signals blink, which is much faster now. any help would be MUCH appreciated because i lost trust in my local Chevy dealership and i am skeptical that the mechanic hooked everything up right when reattaching the cab to frame. I'm just lost and could use some guidance. $13,000 for the truck and i am about $12,000 in in repairs already
It sounds like the truck was doing okay and then the CP4 shit the bed. Then in the course of the repair some stuff didn't go back together properly. I don't know about the leaks but I bet there are bad BCM/ECM/etc. grounds that are causing the weird electrical problems. I'd try a different dealership and see if they can verify that all those modules' voltages are within spec first, then take it from there. If the modules' voltages are out of spec but the charging system is good then it's just a matter of finding the bad connections/grounds and remedying them.

Edit: I reread your post and it really sounds like this is all due to an amateur hour CP4 replacement/rehab job (including the oil leak). Your post suggests that this was done by someone other than the dealership. If so, who? I bet the engine oil leak is also the result of weak sauce reassembly. Unfortunately now that it's been to someone else's shop since that repair you're going to have a tough time getting them to take responsibility. I still say cut your losses and go to a better dealer or reputable diesel specialty shop.
 

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2012 LML 6.6L Turbo Diesel 3500HD4x4 Crew 297K
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7 Posts
Discussion Starter · #5 ·
It sounds like the truck was doing okay and then the CP4 shit the bed. Then in the course of the repair some stuff didn't go back together properly. I don't know about the leaks but I bet there are bad BCM/ECM/etc. grounds that are causing the weird electrical problems. I'd try a different dealership and see if they can verify that all those modules' voltages are within spec first, then take it from there. If the modules' voltages are out of spec but the charging system is good then it's just a matter of finding the bad connections/grounds and remedying them.

Edit: I reread your post and it really sounds like this is all due to an amateur hour CP4 replacement/rehab job (including the oil leak). Your post suggests that this was done by someone other than the dealership. If so, who? I bet the engine oil leak is also the result of weak sauce reassembly. Unfortunately now that it's been to someone else's shop since that repair you're going to have a tough time getting them to take responsibility. I still say cut your losses and go to a better dealer or reputable diesel specialty shop.
yes the CP4 shit the bed and i found a solely "Diesel Mechanic". all the diesel mechanics around me only service semi trucks or powerstroke. the dude who did the fuel system repair didnt seem to on-point after he was done with the job. he had borrowed my 3in to 2in hitch adapter to move stuff in his parking lot, which i dont mind, but never mentioned it and if i hadnt noticed would not have gotten it back. he also didn't have my running boards back on when i came to pick up the truck and almost failed to mention it before me getting the truck. after he drove the truck around to me he hopped out and said "just change this little thing under the dash and all the stabilitrak etc. warnings will go away". i texted him a few days later to ask what exactly he was talking about but he never responded. i did not do any sort of BPP calibration post replacing the old one and did some research today on it and how to do a calibration but all i have is an obd2 reader with torque pro if that is capable? yeah ive already cut my losses and plan to just get it back in order but need to find a real good diesel mech who knows their shit. would it be better to just get a diagram of the grounds necessary to remove the cab from frame and check them all myself? all the grounds in the engine bay look good. the undercarriage is really dirty and when i changed the front hub the speed sensor plug had a brown watery substance come out when i unplugged the old connector. i used electronics parts cleaner and cleaned it out best i could
 

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2012 LML 6.6L Turbo Diesel 3500HD4x4 Crew 297K
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7 Posts
Discussion Starter · #6 ·
Was the bpp sensor calibration completed in the bcm and ecm after it was replaced?
What does bpp sensor data show in the bcm and ecm?
Shorted wire somewhere?
Internal short in the bcm?
Internal short in the tbcm?
no calibration was done. i have an obd2 with torque pro. will that connect or read bcm codes?
 

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2012 LML 6.6L Turbo Diesel 3500HD4x4 Crew 297K
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7 Posts
Discussion Starter · #7 ·
Has your fuse box on the drivers side fender ever been pulled?

Reason I ask is that I pulled mine to add fog lights and a new bumper. After I did this I noticed my passenger side rear running light and right side license plate light would work intermittently. If I wiggled the fuse box, it would work which told me I didn’t have the upper portion properly seated and locked down.

Also I pulled the 40 amp fuse to disable the traction control because I hate it. This fuse is associated with all the idiot lights you listed and all are lit on my dash as well. I cant remember what number it is but it’s shown in the manual.

It really sounds like you’re having a low voltage issue. As for the brake lights, I’d definitely check the wiring in the aftermarket light or put your stock ones back in to see if the issue persists.
i believe it has yes. and that fuse was blown and i replaced it, ill check it again which might be a short in the electrical circuit somewhere. im using the stock brake light housings all idid was replace the stock bulbs with led bulbs because i was having the issue with the stock or what i believe were stock bulbs. who knows what previous owners had done
 

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yes the CP4 shit the bed and i found a solely "Diesel Mechanic". all the diesel mechanics around me only service semi trucks or powerstroke. the dude who did the fuel system repair didnt seem to on-point after he was done with the job. he had borrowed my 3in to 2in hitch adapter to move stuff in his parking lot, which i dont mind, but never mentioned it and if i hadnt noticed would not have gotten it back. he also didn't have my running boards back on when i came to pick up the truck and almost failed to mention it before me getting the truck. after he drove the truck around to me he hopped out and said "just change this little thing under the dash and all the stabilitrak etc. warnings will go away". i texted him a few days later to ask what exactly he was talking about but he never responded. i did not do any sort of BPP calibration post replacing the old one and did some research today on it and how to do a calibration but all i have is an obd2 reader with torque pro if that is capable? yeah ive already cut my losses and plan to just get it back in order but need to find a real good diesel mech who knows their shit. would it be better to just get a diagram of the grounds necessary to remove the cab from frame and check them all myself? all the grounds in the engine bay look good. the undercarriage is really dirty and when i changed the front hub the speed sensor plug had a brown watery substance come out when i unplugged the old connector. i used electronics parts cleaner and cleaned it out best i could
I'd start with a good scan tool and see if you can read the module voltages. If they're within spec then there's no point in doing the exploratory surgery. I have never owned an LML, much less replaced a CP4, much less removed a cab (is that even necessary for a CP4 replacement? And since it was already trashed why not put a CP3 in instead?). I just thought I'd throw out the idea of checking those module voltages first because there are obviously a lot of different problems with the truck right now but it seems like they all stem from the same bad repair job.
 

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2012 LML 6.6L Turbo Diesel 3500HD4x4 Crew 297K
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Discussion Starter · #9 ·
I'd start with a good scan tool and see if you can read the module voltages. If they're within spec then there's no point in doing the exploratory surgery. I have never owned an LML, much less replaced a CP4, much less removed a cab (is that even necessary for a CP4 replacement? And since it was already trashed why not put a CP3 in instead?). I just thought I'd throw out the idea of checking those module voltages first because there are obviously a lot of different problems with the truck right now but it seems like they all stem from the same bad repair job.
ok ill check all the voltages. removing the cab is not necessary but makes it a whole lot easier. he told me i should swap it out for a lift pump in future.
 

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ok ill check all the voltages. removing the cab is not necessary but makes it a whole lot easier. he told me i should swap it out for a lift pump in future.
Yeah that guy is an idiot. A CP4 is an injection pump and a lift pump is...a lift pump. They're completely different devices serving almost completely different purposes. It's like saying you should swap an impact wrench for a toaster oven.
 

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no calibration was done. i have an obd2 with torque pro. will that connect or read bcm codes?
Has to be done in both modules listed.

Only familiar with some of the most current Snap-On scan tools, Blue Driver and GM.

I'd start with a good scan tool and see if you can read the module voltages. If they're within spec then there's no point in doing the exploratory surgery. I have never owned an LML, much less replaced a CP4, much less removed a cab (is that even necessary for a CP4 replacement? And since it was already trashed why not put a CP3 in instead?). I just thought I'd throw out the idea of checking those module voltages first because there are obviously a lot of different problems with the truck right now but it seems like they all stem from the same bad repair job.
No, the cab doesn’t have to be pulled to do a CP4 fuel system replacement and I would also never do it to “make it easier”.
 

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2012 LML 6.6L Turbo Diesel 3500HD4x4 Crew 297K
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Discussion Starter · #12 ·
Yeah that guy is an idiot. A CP4 is an injection pump and a lift pump is...a lift pump. They're completely different devices serving almost completely different purposes. It's like saying you should swap an impact wrench for a toaster oven.
yeah he was saying i should go with a lift pump over the cp4.
 

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2012 LML 6.6L Turbo Diesel 3500HD4x4 Crew 297K
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Discussion Starter · #13 ·
Has to be done in both modules listed.

Only familiar with some of the most current Snap-On scan tools, Blue Driver and GM.


No, the cab doesn’t have to be pulled to do a CP4 fuel system replacement and I would also never do it to “make it easier”.
im just saying what he said.i believe he was wrong lol he sent me pics of the cab on the lift over the frame and said its much easier to do this this way.
 
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