Did a search of the forum but no luck on OBD Code C12D8. Background 2009 Tahoe Hybrid currently has a little over 220k miles. I bought it about 18 mths ago with 195k miles. Put a reman Hybrid battery in around 8 mths ago when it had a little over 200k has been running and driving great up until today. Today just driving along when I got a dash alarm and the dash lit up like a Christmas tree Service Stabiltrac / Service Traction control / Service brakes soon messages rotating through the DIC / Red Brake light lit up / Yellow engine light lit up / traction control icon lit up / ABS icon lit up. No power boost for brakes, brake pedal works at the same height but is really hard to push. Looking at the code description it reads some vague description "ABS Base Brake Open Solenoid Driver Shorted"
These GM hybrids must have a separate electric vacuum pump for the power brakes? I assume that the little vacuum pump has died? Anyone ever had this code or a problem with the power brakes vacuum pump? Note: Cycling the key switch a few times and it did come back on once for a short period of time and I had brake boost but it only lasted for a few minutes. Already dark outside so will have to wait till in the morning to trace the 2 vacuum lines off the master cylinder but glancing at them they appear to go down from the master cylinder and follow the drivers side frame rail towards the rear of the vehicle, so assuming the pump is under the drivers side floorboard somewhere......
edit here 2-16-20 the lines are a supply/return line from the brake master cylinder reservoir to the ABS pressure pump block assembly under the drivers seat area/ All kind of makes sense after crawling underneath. Looks like the control module with 4 small bolts simply fastens onto the valve body and will need to be replaced. No loss of brake fluid the control module is just a bunch of magnetic coils (solenoids) that set over the valve body protrusions to pull the valves on or off. Looks like about a 1 hour project once the new part arrives from rock auto in a few days. Fingers crossed that this fixes the issue. Will for sure post some progress pics and update when i do it.
Spent a couple of hours this afternoon looking around on the internet. Looks like it might be a bad electronic brake control module which contain several solenoids. Best I can tell these coil (aka solenoids) activate to send high pressure brake fluid to individual wheels as needed. Per the DTC description it sounds like a solenoid problem? I wiggled all the wire loom and plug and it made no difference. Rock Auto shows a ACDELCO20896914 part for about 200 bones I think that I will order this one and give it a try. I just cannot justify paying dealership repair cost on a +10 year old + 220k mile beater ride.............. hold my beer and watch this LOL wish me luck boys.
That’s a bummer but 220K things happen. Keep us posted as to results of fix. I’m about 100K behind you but. Build a solutions folder for my future. Plan to run the wheels off it. Thx Paul
Looks like you are on the right track. No "little pump" sorry. almost all the electric brake stuff solenoids pump and accumulator are in that monster under the vehicle.
OK well I have found some very interesting information that might help some GM hybrid and possibly just regular ole GM Truck vehicles with Brake issues.
First OFF Hillbilly is 100% correct this is not a vacuum assist system it is a GM Electro-Hydraulic system. There is a supply and return line from the master cylinder reservoir down to the ABS assembly under the truck tucked up beside the frame rail under the drivers seat area. This ABS assembly includes a high pressure pump/accumulator/valve body and a control module. This assy controls all brake boost/Stabiltrac and ABS. There is a control module with solenoids mounted onto this assy that is easily removable and that is what was bad on mine. It had a seal leak at the top and had gotten water inside which over a period of time ruined the solenoids. It had been leaking long enough that the chrome coating on the solenoids had rusted off in some areas!
Apparently GM's ABS Assembly supplier for these particular parts was not real good at making a 100% gasket seal on their parts. Every time you drive in the rain the part is exposed to moisture this is a BIG TIME mess up on the part of the the supplier! Not sure but I think it is a TRW Kelsey-Haynes supplied part?
When I got the old ABS Control module off it had obvious water damage on the solenoid assemblies on the inside. The seal at the top had been leaking for a very long time and destroyed (shorted) the solenoids. I guess the DTC codes are pretty darn accurate LOL.
Apparently this is a common design throughout the GM truck/utility vehicles in the 2008 / 2009 and maybe up to around 2013. The Chances of mine being the only ABS control module with a gasket seal leaking like this is highly unlikely. Probably thousands out on the road with the exact same issue, they will have a brake issue soon if they have not already!
Anyway I found a used 2009 Tahoe Hybrid ABS assembly (entire assembly) at a local junkyard. Bought it today for $256.00 tax included and swapped the ABS control module off it to my valve body. Took less than a hour. Note: I had ordered a new ABS control module from rock auto at $199.00 but canceled that order this morning because I was afraid that I would have to go to the dealer to get it flashed to match the vehicle.
That dealer flash process would have added a lot of time and cost (probably $100.00 min to flash at dealer?) Just be careful to double check your RPO code if a Hybrid it will most likely be a J92 RPO Code for 7,700 lb active brakes. It seems to be very happy coming from a nearly identical Hybrid into mine so no dealer reflash required.
I have driven around for about an hour and all DTC codes and dash lights are out and it drives normally. So far so good, knock on wood.
Got some pics here...........if you want more pics let me know and I will send them to you. I am going to keep the junkyard assembly for a while until I make sure everything is 100%. Junkyard part tag interesting that is has the donor VIN on tag Valve body on my Tahoe had to clean the top seal surface Small hands can reach the bolts easily Water Contaminated Old Part pulled off today 2-17-2020 Junkyard assy off a 2009 Tahoe Hybrid J92 RPO code part Another view of the junkyard assy Part numbers for the water contaminated pc that came off my 2009 Tahoe Hybrid
OK well I have found some very interesting information that might help some GM hybrid and possibly just regular ole GM Truck vehicles with Brake issues.
First OFF Hillbilly is 100% correct this is not a vacuum assist system it is a GM Electro-Hydraulic system. There is a supply and return line from the master cylinder reservoir down to the ABS assembly under the truck tucked up beside the frame rail under the drivers seat area. This ABS assembly includes a high pressure pump/accumulator/valve body and a control module. This assy controls all brake boost/Stabiltrac and ABS. There is a control module with solenoids mounted onto this assy that is easily removable and that is what was bad on mine. It had a seal leak at the top and had gotten water inside which over a period of time ruined the solenoids. It had been leaking long enough that the chrome coating on the solenoids had rusted off in some areas!
Apparently GM's ABS Assembly supplier for these particular parts was not real good at making a 100% gasket seal on their parts. Every time you drive in the rain the part is exposed to moisture this is a BIG TIME mess up on the part of the the supplier! Not sure but I think it is a TRW Kelsey-Haynes supplied part?
When I got the old ABS Control module off it had obvious water damage on the solenoid assemblies on the inside. The seal at the top had been leaking for a very long time and destroyed (shorted) the solenoids. I guess the DTC codes are pretty darn accurate LOL.
Apparently this is a common design throughout the GM truck/utility vehicles in the 2008 / 2009 and maybe up to around 2013. The Chances of mine being the only ABS control module with a gasket seal leaking like this is highly unlikely. Probably thousands out on the road with the exact same issue, they will have a brake issue soon if they have not already!
Anyway I found a used 2009 Tahoe Hybrid ABS assembly (entire assembly) at a local junkyard. Bought it today for $256.00 tax included and swapped the ABS control module off it to my valve body. Took less than a hour. Note: I had ordered a new ABS control module from rock auto at $199.00 but canceled that order this morning because I was afraid that I would have to go to the dealer to get it flashed to match the vehicle.
That dealer flash process would have added a lot of time and cost (probably $100.00 min to flash at dealer?) Just be careful to double check your RPO code if a Hybrid it will most likely be a J92 RPO Code for 7,700 lb active brakes. It seems to be very happy coming from a nearly identical Hybrid into mine so no dealer reflash required.
I have driven around for about an hour and all DTC codes and dash lights are out and it drives normally. So far so good, knock on wood.
Got some pics here...........if you want more pics let me know and I will send them to you. I am going to keep the junkyard assembly for a while until I make sure everything is 100%. Junkyard part tag interesting that is has the donor VIN on tag Valve body on my Tahoe had to clean the top seal surface Small hands can reach the bolts easily Water Contaminated Old Part pulled off today 2-17-2020 Junkyard assy off a 2009 Tahoe Hybrid J92 RPO code part Another view of the junkyard assy Part numbers for the water contaminated pc that came off my 2009 Tahoe Hybrid
Is this on the drivers side just behind the rear cross member? Is it something we might want to make an rtv gasket for?
Yes the ABS assembly is on drivers side almost directly underneath the seat tucked up beside the frame rail. You have to pull off the plastic cover to access it. (2 bolts and 2 plastic clips)
I forgot to mention that YES I DID use a nonhardening formagasket product when I put the junkyard piece back onto my valve body to make 100% sure that it is sealed. I saw in several places on line to NEVER use a RTV or other sealer on that installation but I am not sure why that is. Some silicones could affect the solenoid operation maybe? The permatex nonhardening formagasket is pretty benign I really do not think it will hurt anything? If it does i guess that i will know soon enough!
Hopefully it will stay dry inside the module and will be good for another few years and around 80k miles (my goal is to get 300k out of the ole beater currently at 220k)
Thinking back I may be messing up by running my Ho through the local automatic car wash, it does a undercarriage spray that may have contributed to the issue but man $19.99 per month for unlimited car washes and free vacuum with free towels is an irresistible deal..................Ole HO looks pretty when she is cleaned up, with or without working power brakes LMFAO
Yes the ABS assembly is on drivers side almost directly underneath the seat tucked up beside the frame rail. You have to pull off the plastic cover to access it. (2 bolts and 2 plastic clips)
I forgot to mention that YES I DID use a nonhardening formagasket product when I put the junkyard piece back onto my valve body to make 100% sure that it is sealed. I saw in several places on line to NEVER use a RTV or other sealer on that installation but I am not sure why that is. Some silicones could affect the solenoid operation maybe? The permatex nonhardening formagasket is pretty benign I really do not think it will hurt anything? If it does i guess that i will know soon enough!
Hopefully it will stay dry inside the module and will be good for another few years and around 80k miles (my goal is to get 300k out of the ole beater currently at 220k)
Thinking back I may be messing up by running my Ho through the local automatic car wash, it does a undercarriage spray that may have contributed to the issue but man $19.99 per month for unlimited car washes and free vacuum with free towels is an irresistible deal..................Ole HO looks pretty when she is cleaned up, with or without working power brakes LMFAO
sure you can get a bit more then 300k out of it 400k at the most if taken care of
Have this EXACT thing going on with my 2011 Escalade right now... thanks for sharing now I know what to order. Which is why I checked the forum..carid has it for $201
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02-15-2020, 04:03 PM
C12D8 No Power Brakes lost all boost
