C121E That Persists

[ConorToot]

I’ve read your latest post so far three times.

Did you reuse the brake fluid reservoir on the master and did you replace the vacuum line off the master brake cylinder with a new one and use a clamp ?

No used the new one that came with it.

I think I found the issue and solved the problem, but since it would go away for as long as two days, I don't want to hold my breath until its been a week, possibly more.
With only the ABS pump and control module and the brake booster left that I haven't replaced, I automatically was looking at the ABS equipment and the ECU, as the information that I read said the ECU could cause this. I've already cleaned connectors and I even took the ABS control module apart and re-flowed the solder joints. I was more concerned about the pump or that I might have goofed up when I rebuilt the ABS control module (I had to use a torch lighter to get the 50-ish pin connector de-soldered to get to the other side of the board. I'll be honest, I thought I wasn't going to be driving to work the next day, but it worked.
So, yesterday, Saturday February 24th, I was sitting in my room looking over schematics at almost midnight, then I watched some YouTube videos of how to rebuild a brake booster which they seemed pretty straight forward. I was thinking that I would bite the bullet and order a replacement booster, but when I looked, they were very, very difficult to find new. I'm not into putting used or remanufactured parts on my truck. The reason they are remanufactured is because they broke and I'm not one to put broken parts in as a replacement, nor do I like doing things twice. Then, I saw a video of a guy explaining the vacuum valve and telling the audience to check it with a vacuum pump, etc. It occurred to me that I hadn't done this simple test.
At midnight, I went out to check the vacuum valve and lines. When I went to pull the valve from the booster, I noticed it wasn't seated all of the way in, which at first didn't alarm me. I checked the valve with about 20psi of vacuum pressure and it worked great. I reinstalled it and did something my brother-in-law had recommended that I already checked, but thought it wouldn't hurt to do it again and that is to pull a vacuum from the vacuum valve with it installed to check the booster's diaphragm for leaks. It was fine. A little dejected, I got in the driver's seat and reset the fault code and took it for a spin (also to get some late night Whataburger).
Typically, it only takes a few minutes for the light to come on, but I noticed after my munchie stop that it still wasn't on. This wasn't shocking as I've had it go two days without coming on. The more I drove the more I recalled the valve not being fully seated and pondered how this could cause a comparative pressure whatever it says for C121E in oddly phrased diagnostician English. This morning, I got up and had to run to the grocery store. The light was still off. I drove it once in the afternoon and by this point, it would have likely come back on by now, but it was off. When I got home, I pulled the valve again to inspect the seal. It wasn't bad and the valve fit fairly tight, but it was pretty dry. The rubber still had a decent spring to it, but I could see how it might not seal well against the hard plastic of the valve itself. I had an assortment of good quality o-rings in my garage, so just for s&giggles, I found one that was a fat o-ring with lots of bounce and a snug fit for where the valve mates up to the booster seal. It was installed and I went on another drive. Still no light. I'm about to hit a grocery store for some lunch supplies and maybe its still sealed and the light is still off? Like I said, I'm not holding my breath because nothing pointed me in this direction and I don't know why that seal with a leak would cause a C121E fault. If anyone has a hypothesis, I'm all ears.

I’ve read your latest post so far three times.

Did you reuse the brake fluid reservoir on the master and did you replace the vacuum line off the master brake cylinder with a new one and use a clamp ?

 

[ConorToot]

Nope! It was fine on the 7 mile drive to the store, but on the way back, the light returned. For reference, I was driving steadily at 40mph with my foot very lightly on the gas pedal to maintain the speed, very steady RPMs, going straight, I was not turning, on a smooth, well maintained road. No indication that something changed with the vehicle other than the light appearing on the dash. I pulled over and reset it, then I checked the booster valve. It had so much vacuum that I couldn't pull it free. After resetting it, it came back on within two or three miles of driving. I reset it again, and it came back on when I made my first turn. Tomorrow, I might start tearing apart connectors and other modules to see if anything looks like it might not be up to par.

 

[ConorToot]

Today during my lunch break, I was driving with the codes cleared and the traction control light illuminated. I hit the brakes right when it illuminated to see if there was something instantaneous that was gone by the time I would need the brakes. For the first time since I put new brake calipers on it, it pulled to the right significantly. Strangely, I was happy it didn't brake perfectly straight. I pulled over and took a glance and noticed, again for the first time since I've owned it, it had an actual leak because there was brake fluid slung across the inner tire.
When I got home I pulled the front left wheel off to check out the caliper. The caliper was seized, but I didn't find any leaks from the pistons or anywhere. I went ahead and cleaned up the caliper and did a much better grease job to keep it from seizing and reassembled it. It moved well after I cleaned it up, but I know I'll be taking it off soon.
As done with one wheel, it is wise to do the same with the other. The same process was repeated with the right wheel, except when I got the caliper off, about half of the piston boot was missing. I smeared some grease on it which should keep it until I can get some caliper rebuild kits and get both the left, where I couldn't find the leak it is probably a piston seal, and for the right where the boot must get replaced or I'll be getting new calipers if I don't fix it soon.
On a test drive after fixing the slides and bleeding the brakes, the code was gone and didn't come back for the whole drive. I'll keep watching for the light to come back because it most likely is a stuck valve in the ABS module.

 

[ConorToot]

Nope! It was fine on the 7 mile drive to the store, but on the way back, the light returned. For reference, I was driving steadily at 40mph with my foot very lightly on the gas pedal to maintain the speed, very steady RPMs, going straight, I was not turning, on a smooth, well maintained road. No indication that something changed with the vehicle other than the light appearing on the dash. I pulled over and reset it, then I checked the booster valve. It had so much vacuum that I couldn't pull it free. After resetting it, it came back on within two or three miles of driving. I reset it again, and it came back on when I made my first turn. Tomorrow, I might start tearing apart connectors and other modules to see if anything looks like it might not be up to par.

Does anyone know where to get a 54mm diameter x 54mm height steel brake caliper piston?

Okay, so the code keeps coming back and now, my truck pulls to the right when I brake. Checking the front left wheel (pulls right when braking / left brake issue) the brake was frozen, meaning it was not engaging. It was disassembled and the slide pins cleaned thoroughly and re-greased. I checked the pads and they seemed okay.
Do to the right what you've done to the left for brakes (a rule I keep in mind). I pulled off the right brake that was working well and one of the pistons was missing half of the boot and the other piston boot has a big cut. The slide pins were cleaned and re-greased. The pads looked okay. I reassembled the brake and put some grease over the cut boots while I found rebuild kits.
I have no idea what cut the boots on that caliper, but I ordered some rebuild kits for the front since no one had any locally. They arrived and of course were wrong. I'm currently waiting on the right ones to arrive.
After driving for two days, the front left froze again causing the truck to pull right. The front brakes were checked again and this time a noticeable splatter of brake fluid fanned out across the inside of the front left tire. The brake was definitely frozen and not squeezing the disk. I took the caliper off and started looking at it. The spec sheet for these calipers claims that they have steel pistons, which is why I purchased the AC Delco calipers and paid more. But when I removed the front left rear-most piston and a chunk came off of it about the size of a quarter and about 1/2" deep, I understood that they have the wrong information for this caliper because these are phenolic, which won't work for long in the Gulf Coast region. They shatter because we have normal, everyday rainstorms that bring a couple of inches of rain. Hot brakes hit that water and this causes the phenolic pistons to shatter. Phenolic pistons are good at dissipating heat but not for going from hot into drenching them with cool water. Sure, the brake fluid doesn't boil, but people are driving around this region with shattered brake pistons and don't know it, and don't care.

I'll stop there and keep this short ----- Does anyone know where to get a 54mm diameter x 54mm height steel brake caliper piston?

I don't want to drive on something that crumbles every time we get a gully washer.

 

[ConorToot]

Even though the calipers that I replaced less than a year ago were brand new, not remanufactured, and definitely not used, they might get replaced again. It seems that they, are going to be phenolic piston garbage, just as the original ones that I replaced with four shattered pistons. No one that I can find sells steel brake caliper pistons by the diameter or size. Every vendor I've found asks, "what's the vehicle make, model, and year?" My response, "AC Delco 15FR2530 brake calipers with a 54mm diameter and 54mm length piston." doesn't seem to work and then I get the wrong part that doesn't fit these calipers in the mail even though I requested exactly what I need, they send the original fitting parts that don't fit these calipers. There was a reason that I switched to these calipers, they had steel pistons, supposedly. However, they didn't. They were the same garbage that was in the truck originally, the new ones are just slightly different so nothing fits because dumb people who obey their computer masters ask the type of vehicle I have and send the original fitting parts even though I tell them that I have different calipers, these people simply can't listen because Idiocracy has already happened and we are now collectively more dumb than ever.
When I decided to rebuild the current calipers with steel pistons, it proved to me that we are even more dumb than before because I can't search for a 54mm OD diameter piston and get anything at all other than a return of the question, "Year, make, model?" which no longer applies if you go maverick on the vehicle and change something away from standard OEM parts. God forbid a person rubs their two brain cells together and has a bright idea of changing something that sucks about their vehicle to improve it because they are stuck on an island alone thereafter as their vehicle has a uniquieness that eliminates them from obtaining parts by specifications other than "Year, make, model".

 

[ConorToot]

First I want to thank anyone who offered assistance or even read my stupid stream of thought long posts. Seriously, thank you.

Second, I'm feeling more confident that I found the problems that caused the error code or contributed to a year and a half of the cartoon out of control car light that irradiated my face from its permanent home at the bottom right of the instrument cluster.

Problem 1: My calipers had bleeder screws that weren't a match. I replaced them twice by matching the previous bleeder screw. The third time, I looked up the caliper and the spec for the bleeder screws that were called for on the spec sheets. They didn't leak, but they made bleeding the brakes pretty much impossible to accomplish without air getting into the calipers through the thread. Also, never use tape to seal the threads. It melts when the calipers get hot. Use thread sealer paste because it holds up to the heat very well and does an amazing job of sealing the threads.

Problem 2: I'm still searching for metal caliper pistons and have yet to find any that are between 54mm and 55mm in diameter and height. Last weekend, I received four Mopar "guaranteed to be steel pistons" that were phenolic and angered me greatly as they cost $80 and weren't what I wanted. From attempting a rebuild the weekend prior, I already knew I had one piston that had to be changed asap when I only took one caliper off and realized that someone who "guaranteed the correct boots and seals for a 2012 Ram 1500 SLT" was way off and they didn't work. After going through all four calipers that were bought brand new and installed less than a year ago, of the 6 pistons, 3 were damaged beyond being able to use. One piston on each front caliper was crumbled, shattered, or had a significant break with piece that made the piston multiple pieces, and one rear piston was broken significant enough that Ihad to clean out the dust and crumbles from the caliper. To get by, I used two of the original front pistons that were salvageable on the back calipers. They are taller but are the same diameter. One of the pistons has a fracture in it but was used because it was the best of the remains I had to fill that caliper.

*** If anyone knows where to find metal pistons that are 54-55mm diameter and 54-55mm in height, I really need to get all of these replaced asap before it rains and these shatter from rapid cooling. Please, please, let me know because it sucks to drive with questionable brakes.***

Problem 3: Because my brake pedal would harden and stop the truck very rapidly, but then the pedal would sink to the floor, I had replaced the master cylinder a few weeks ago, but that wasn't the issue. I got a used ABS unit that was the pump, valve body, and control and installed it yesterday and last night. At first the traction control warning light looked like it had a party and invited all of it's blinking and beeping friends. Until 3:30 AM I went through and addressed each one in the configurations for the ABS module. What was sold to me as an exact match per the VIN# I provided, wasn't a match. This replacement was off of a 4x4 and I have a RWD. I got it working and matching almost everything, cleared the C121E fault, then went to work and drove an extra two hours after work, and the light has not returned. It does give a U0102 fault for "no communication to the transfer case, AWD", but I don't think my truck has one of those. Unfortunately, I have not found any settings that seem incorrect using AlfaOBD, but I've also searched for anything on AlfaOBD relating to "transfer case" and AlfaOBD hasn't found any settings that it has for a transfer case in any reference.

I won't feel truly confident that it's fixed until I can clear the new fault code and drive for a week or two. However, by then might be in need of six more repacent dust pistons as these are made of the most fragile material in the known universe.