ESP/BAS light - aka ABS issue

Hi all,

I'm popping my posting cherry on this one. I have a 2005 Magnum RT and bought it used from a private seller about a year and a half ago with 50K miles on it. It's at 77K now. It's got a nasty gremlin called the ESP/BAS light and the dealership can't seem to find a cure. I'm not a mechanic but know enough about cars to understand how they work. I've replaced minor components on other cars myself such as alternators and starters. So, talk the talk and I'll get the idea.

The recurring code is C121D. I'm at the dealer at least once a month with this problem since I got the beast but haven't paid for a repair in a year. You name the brake component and they've replaced it. I really get the feeling it's an electrical issue. They're currently working with Chrysler engineering and I've been waiting for a solution for almost a month now. I bug them twice a week to keep them honest.

Has anyone else had this issue? Sadly, I haven't been able to enjoy my car because of this. Thanks in advance!

~Nomad

C121D-BRAKE PRESSURE SENSOR CIRCUIT
Set Condition:
When the Anti-Lock Brake Module indicates that the Brake Pressure Sensor Signal is out of range.

Possible Causes
TERMINAL/CONNECTOR/WIRING HARNESS DAMAGE
AIR IN BRAKE SYSTEM/WORN MECHANICAL COMPONENTS
(B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT SHORTED TO VOLTAGE, GROUND, OR OPEN
(B984) BRAKE PRESSURE SENSOR RETURN CIRCUIT SHORTED TO VOLTAGE, GROUND, OR OPEN
(B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT SHORTED TO VOLTAGE, GROUND, OR OPEN
BRAKE PRESSURE SENSOR
ANTI-LOCK BRAKE MODULE

I would also have the speed sensor checked

Also do you have the traction control delete mod?

is the car tuned by chance? you can turn of the ESP/BAS with the predator and that will cause the light to come on. its not advisable to do that though..

Thanks for the response. No mods on the car.

Brake pressure sensor was replaced a couple of times.
Wiring harness connector was replaced. (The dealer wasn't prepared to eat the $900 cost of a whole new harness.)
Brakes have been bled a few times by the dealer after repairs.
Anti-lock brake module has been replaced a couple times.
Travel sensor was replaced.
Power brake booster was replaced.
Stop lamp switch was replaced.
Master cylinder/booster pressure sensor replaced.

Once after replacing the ABS module the tech noted that the brake pressure was reading 2230 psi which the service manager admits is impossible. That would blow the line. The notes on the service order were, "inspect sensor and connector for damage and found the connector green and white wire damage by water corrosion. Removed wire and splice new one. Then after repair pressure was fluctuating from high to low. Check wires from connector to ABS module connector and found more water damage or corrosion inside the connector. Clean and repair ground wire for the pressure sensor."

This has been my biggest red flag for an electrical issue, not just a sensor or module problem. Besides random condensation, how or why would those wires and connectors corrode unless water was somehow traveling to that point from somewhere?

On another note, there seems to be no rhyme or reason to the atmospheric or driving conditions that set off the codes. It's happened in all weather conditions, dry and wet, hot and cold, humid and dry. I could be stopped at a light or cruising down the road. Recently it came on right when I turned the key to start the car and stayed on.

I know Mercedes had a hand in the design as the company was Daimler-Chrysler back then. I've read about some Mercedes having that light come on, as well.

~Nomad

you bought it used... it could be a flood damage car...

as for corrosion i dunno. i had 3 wires that pass through one connector that had corrosion for some reason in my drivers door. once in a rare while the door wouldn't register that it was open or turn on the interior lights when i opened it. when i was wiring in my led door logo projector lights i found the wires were corroded on one side of the connector to the door. i had to splice like 3 wires to bypass the door plug but i haven't had the problem since.

i think they didn't put rubber boot back on right over the door wires when the previous owner installed the mirror turn signals (the only mod my car had when i bought it) and water got into there.

Any new updates on this?
Ive heard of something like this happening from something in the steering wheel column, ill check if i can find the link on the other forum.
Also another check was to recalibrate the computer by doing a fuse pull or battery disconnect and turning the wheel all the way to the left and all the way to the right.

lxforums dot com/board/f77/esp-bas-light-294652/

Thanks for checking up again. The computer reset has been done a number of times by the dealer and I've done the steering wheel trick, too. That one is actually in the owners manual! That should have been a red light to begin with, right?

Thanks for the link. I am extremely hesitant to take it back to the dealer I've been going to (Hawk Chrysler/Jeep in Forest Park) as they have never actually fixed the problem. I walked away when their final solution, on advice from Chrysler Engineering, was to just replace the whole wiring harness which is about $1800 for the harness (my cost) plus labor (their cost). They didn't even sound like they knew it would fix the problem. Incompetence, I say. I will see about getting the steering wheel checked as mentioned in the other forum, though.

Thanks again,
Cobalt

Well what was the outcome?

We had baby number 3 at the end of June so I've pretty much been ignoring the problem. My brother bought a 2008 Grand Prix and cleaned off some corrosion off the battery terminals which resulted in his ABS light coming on. His problem went away but was a lesson to me that ABS systems are fickle beasts with minds of their own.

Aha well let us know when u get to it

Update: Well I took it to a mechanic near work, H&R Towing and Auto Repair in Forest Park. Believe it or not, they found and fixed (more or less) the problem. There were loose wires in the pigtail coming out of the ABS module that were the culprit. Essentially this caused a short which gave a false code. Many thanks to these guys! It only cost me about $140, too.

I had taken my wife's car there to replace the timing belt and told them about my headache. They really wanted to take a shot at it so I told them they had one chance. They convinced me because they showed me the program/service they use. On the surface it is a database of auto problems so they can see what other cars have had similar issues. But there are also reps they work with to help diagnose problems step by step. The dealer, as we all know now, just replaces parts until the problem (or customer) goes away.

So the mechanics at H&R checked the voltage on each wire until they found the bad one. Because the connector is no longer available unless you get the whole wiring harness (for the entire car, $1800) with it they were able to just tighten up the connection and wiring loom to keep things in place. The ABS light did come back on a couple times so I took it back and they re-tightened the wires and it hasn't been a problem since. I suspect the issue will continue to resurface but I am extremely happy and grateful they found the real problem.

Give these guys a call if you need a repair. They seem to be on the up-and-up. They even show you the old parts they replaced without having to ask.