2012 Ram Outdoorsman 27,171 kms.

Well the deep freeze finally broke this weekend for a couple of days anyway. On Monday of this week the temps were above the freezing mark. While going down my driveway, the brake pedal dropped close to the floor and was hard to stop. When I reached the road I haul over and applied the brakes and all was fine, except the abs warning light was on. Took the the dealer today and they told me the brake pressure sensor needs to be replace, they ordered the part today. Is this a common problem? I had a 1998 Ram 1500 for 14 years and never had a ABS problem.

Where is the brake pressure sensor located?

Thanks
Kayakman

 

Never heard of such a thing. When they get the part # on the repair order, I'd be curious to see what it actually is. I think the only sensors that affect the breaking are the wheel speed sensors. The system does go through a self test at start up so maybe there is some kind of sensing going on that they need to fix. Maybe TNtech knows about this sensor.

 

I think they may be talking about the Dynamics sensor. It's used as part of the ABS electronics. It's located under the front seat in the middle hump just to the left of the drivers seat belt controller (MODULE-OCCUPANT RESTRAINT CONTROLLER).

OPERATION

Battery voltage is supplied to the ABM. The ABM performs a system initialization procedure at start up. A check of the ABS motor is performed at 15 miles per hour. Initialization consists of a static and dynamic self check of system electrical components.
The static and dynamic checks occurs at ignition start up. During the dynamic check, the ABM briefly cycles solenoids to verify operation. An audible noise may be heard during this self check. This noise should be considered normal. The ABS motor and pump are then checked at a speed of 15 mile per hour.
If an ABS component exhibits a fault during initialization, the ABM illuminates the amber warning light and registers a fault code in the microprocessor memory.
The ABM monitors wheel speed sensor inputs continuously while the vehicle is in motion. However, the ABM will not activate any ABS components as long as sensor inputs indicate normal braking.
During normal braking, the master cylinder, power booster and wheel brake units all function as they would in a vehicle without ABS. The HCU components are not activated.
The purpose of the antilock system is to prevent wheel lockup. Preventing lockup helps maintain vehicle braking action and steering control.
The antilock ABM activates the system whenever sensor signals indicate periods of wheel slip.
The antilock system prevents lockup during a wheel slip condition by modulating fluid apply pressure to the wheel brake units.
Brake fluid apply pressure is modulated according to wheel speed, degree of slip and rate of deceleration. Sensors at each wheel convert wheel speed into electrical signals. These signals are transmitted to the ABM for processing and determination of wheel slip and deceleration rate.
The ABS system has four fluid pressure control channels. Each wheel brakes are controlled separately. A speed sensor input signal indicating a wheel slip condition activates the ABM antilock program.
There are Two solenoid valves (Isolation and Dump valve) which are used in each antilock control channel. The valves are all located within the HCU valve body and work in pairs to either increase, hold, or decrease apply pressure as needed in the individual control channels.
During an ABS stop the ISO valve is energized which acts to prevent further pressure build-up to the calipers. Then the Dump valve dumps off pressure until the wheel unlocks. This will continue until the wheels quit slipping altogether.

 

Got the truck back. -----

The words of the tech who worked on the truck
Complaint --- scan test and check cause of abs light on and scan abs light found code
Cause ------- C121E - brake pressure comparative performance
Check and found the brake pressure switch working intermittently
Correction -----order new switch
replace switch
part number------ 56038914-AC switch 08-058-060

So is this the little brake switch found above your brake peddle .. $10-15 part??

If this is true-- if the brake switch not working it would cause the the same as what you have stated Pedro? just another cause...

 

If you google the switch, yes it's the brake pedal switch 10$ part.

If you google the code, it seems there are many other components involved. A link below describes the diagnosis procedure on a jeep (similar I'm sure to ram trucks).

http://www.clubcj.net/workshop/SEARC...0013300ENG.HTM

I have had the same symptoms twice now but without any error codes myself. Luckily not on the highway, but doing 40km on residential streets could be even more fatal.


My daughters boyfriend told me last week he's replaced 4 master cylinders that week due to "shrinking seals" on pressure switches.

 

Wow - is this a problem for jeeps, or ram and jeeps? I was just going slowly down my steep driveway when this happened. Part #56038914AC replaces: 56038914AA, 56038914AB, so is this a fix. It seems to have a more audible click than the original.

Thanks Pedro Dog and Owensue

 

At least you know that it's an easy fix next time, if it ever happens again. These new trucks have so much software that even this switch can mess up the logic. Sounds like a "bouncy" switch that jacks up the whole enchilada. I just learned something.

 

the brake pedal felt as if your engine was off and you press down and it goes almost to the floor on the first pump. I bit scary ---

 

kayakman and Owensue,

Glad to hear nobody was involved in an accident. @Owensue, is the issue still occurring or have you had an opportunity to run it by your service dept.?

@kayakman, I hope I'm on the right track here, has the switch been replaced? Are you still experiencing the issue with the brake pedal?

If you guys are having trouble beyond this, feel free to PM me.

Take Care,

 

It was replaced on Thursday DodgeCACares. It seems to have a more audible click than the original. As I said yesterday, It was replaced with Part #56038914AC replaces: 56038914AA, 56038914AB (found this info on the net). Which seems to tell me there might be an issue with this little devil of a part.

cheers