How does collision advoidance system activate the brakes

[Caseyjay]

I am troubleshooting DTC codes that are unexplained. In my thinking,, I pondered, the possible interaction of the automatic collision avoidance braking system works. I am not asking how it is triggered or is sensed. What I want to know is, once it is activated, how are the brakes actually applied. For instance it might be separate vacuum line to brake booster or hydraulic piston on brake lines or electric motor or solenoid on pedal. Would appreciate the answer to this question and any relevant circuit information as well. Thanks

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[airline tech]

I am troubleshooting DTC codes that are unexplained. In my thinking,, I pondered, the possible interaction of the automatic collision avoidance braking system works. I am not asking how it is triggered or is sensed. What I want to know is, once it is activated, how are the brakes actually applied. For instance it might be separate vacuum line to brake booster or hydraulic piston on brake lines or electric motor or solenoid on pedal. Would appreciate the answer to this question and any relevant circuit information as well. Thanks

What are the codes?

The ABS, Collision Avoidance, Cruise Control, Traction Control etc systems all tie together,
Any fault detected in the system can deactivate other systems.

There is no easy detailed explanation of exactly how it activates.
The ABS Module controls the solenoid valves within the HCU allowing brake pressure to be applied to the calipers (pre-charge) to close the gap between the pads and the rotors.
If the system determines collision is -imminent then the ABS Module activates the Pump and applies full brake pressure.

 

[Caseyjay]

Thank you! I am getting that there is a solenoid on the brake hydraulic system that is actuated to activate the brake calipers, am I correct in my understanding? I am towing this Ranger behind my motorhome with a stay-in-play braking system. While I am braking the coach, the Ranger pedal is pulled down with an air piston which is normal. But every so often with a hard stop, I see the Ranger pedal suddenly plunge downward which causes a clunk. When this occurs, a DTC code of B 148 D is set. Also a warning flashes on the display saying Check Brakes. The code indicates a short to B+ or open on Stop Output circuit. I have wondered if somehow, the Ranger initiated an emergency stop. I had hoped that no one would have designed it so that any of those auto braking systems would be active while being flat towed, but.. you never know.

 

[RangerBill]

There is a motor inside the ABS module to drive the HCU (hydraulic control unit) to increase braking hydraulic pressure.

 

[Msfitoy]

Does anyone have the balls to actually drive towards a wall and test this out? If the brakes actually activate, would it stop in time to prevent contact? $20 for volunteer...

 

[Caseyjay]

There is a motor inside the ABS module to drive the HCU (hydraulic control unit) to increase braking hydraulic pressure.

Ok, if I could pull a fuse for that system, I could test to see if that stops the pedal slam. I would not think that the ABS system is necessary to braking the Ranger while it is being towed

 

[Cabose-1]

Has anyone had the balls to actually drive towards a wall and test this out? If the brakes actually activate, would it stop in time to prevent contact? $20 for volunteer...

Well, unless this is on an upper trim level ranger, i rear ended a pickup truck a few months ago, and no brakes came on. I have an xlt fx2 with no adaptive cruise. Seen the warnings but never felt brakes applied or car slow down or depower itself

 

[Caseyjay]

Has anyone had the balls to actually drive towards a wall and test this out? If the brakes actually activate, would it stop in time to prevent contact? $20 for volunteer...

If you think about it, being in the Ranger while it is being towed. The RV starts braking, the Ranger starts braking but there is a large motorhome just 6 ft away from your truck and as the brakes are applied ever stronger, the distance to the RV is still 6 ft. Then the Emergency Braking System lurches into panic. This is how it seems to me, but then I think nobody could be stupid enough to keep these systems active while being flat towed.

 

[RangerBill]

DTC B148D seems to point to the stop lamps circuit having a problem. What is the entire DTC code? Do you have something wired into the stop lamps? Could your brake pedal actuator be rubbing against the brake pedal wiring?

 

[RangerBill]

Ok, if I could pull a fuse for that system, I could test to see if that stops the pedal slam. I would not think that the ABS system is necessary to braking the Ranger while it is being towed

Fuse F82 in the Battery Junction Box (60 amp) feeds the HCU motor.

 

[Caseyjay]

Fuse F82 in the Battery Junction Box (60 amp) feeds the HCU motor.

Thank you, I will try without fuse 82 and see if it helps. The stop lamps are wired with diodes to the RV. The factory right stop wire is broken and a diode inserted cathode to the light. Another diode is attached cathode to that cathode which. The anode of the second diode goes back to the stop/turn of the rv. The circuit on the left side is the same. I could understand some back feed current though the back biased diode, but it would be there always not just when I get the pedal slam.

 

[RangerBill]

Here is another post discussing the same problem.
https://www.ranger5g.com/forum/threads/flat-tow-supplmental-braking-issue.4005/

 

[airline tech]

Note: I do not Flat Tow nor do I have an in-depth knowledge of the Stay N Play (Demco) unit

Ok I see what is happening, now that I know you are Flat Towing.

Here is the operation of the system and why you are getting a hard braking action on the truck to match the motor home, now I am not exactly clear on how your added system operates (brake control) but it appears to match the motor home.
If you brake hard on the motor home, it's telling the truck to brake hard.

When the truck brakes hard, it's not running so no (Brake Booster Vacuum), and the ABS Module sees this and commands the HCU & Pump On, to obtain the braking action needed.

But to confirm here, the Stay n Play unit - has its own pump to provide booster vacuum, Correct?

If YES:
You may try Fuse 82 - Feeds the Pump, note fuse 82 is on the bottom side of the fuse box, kind of a pain to get access to it.
I believe there was a post or video on how to get access
The reason being if you depower the pump then you will eventually deplete proper normal braking action without an alternate pump.

Ref: This thread on a similar issue, poster mentions a revised tube on the brake booster

P103C and no brake boost in reverse? | 2019+ Ford Ranger and Raptor Forum (5th Generation) - Ranger5G.com

 

[airline tech]

If you think about it, being in the Ranger while it is being towed. The RV starts braking, the Ranger starts braking but there is a large motorhome just 6 ft away from your truck and as the brakes are applied ever stronger, the distance to the RV is still 6 ft. Then the Emergency Braking System lurches into panic. This is how it seems to me, but then I think nobody could be stupid enough to keep these systems active while being flat towed.

The CCM and IPMA for that side of the Emergency Braking System are not powered during Flat Tow, they are powered with the Run/Start Relay Circuit.
However, the ABS Module itself is Always Hot, so it's not picking up a Collision Signal and activating, it's the Brake Booster Vacuum Loss triggering the pump on.

 

[Tim H.]

Does anyone have the balls to actually drive towards a wall and test this out? If the brakes actually activate, would it stop in time to prevent contact? $20 for volunteer...

The first week I owned my Ranger a woman in front of me stopped suddenly as I was moving to the right lane with my head turned to the right to look for oncoming traffic. My truck stopped on a dime by itself and the crash avoidance indicator lit up and gave off a loud beep.

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