Parking Brake Sensor Fixed

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Parking Brake Sensor Fixed

August 15, 2020, 06:13:00 pm

This was a leftover from my Motorhomes of Texas visit. The parking brake dash light originally lit when I hit bumps, but got to where it would make a low level flash and you could hear a weak alarm sound pretty much all the time.

I had a separate symptom where I could hear a small air leak as the engine started and aired up. Once the motorhome got above about 40psi, the leaking stopped. I original thought this was from the sensor, but since it doesn't have any pressure on it when parked, I decided it was the valve.

The parking brake valve has one input (supply) and two outputs (delivery). One goes to the parking brakes and the other goes to a switch that turns off the Parking Brake light on the dashboard.

The first photo shows the parking brake valve behind the dash with the supply line (top) the delivery line (our left) and the sensor (our right) with green, white, and blue wires going to it. The second photo shows the sensor removed. The original sensor was a Hobbs S76578 normally closed 10psi switch. I replaced it with a Haldex BE13421 that I got from NAPA. The Haldex switch is physically bigger, but still fits. It's not the right switch and turns off at 66psi instead of the Hobbs at 10psi. Not really an issue in practice. You'll just get a Parking Brake light at the same time you get a low air light when you're in trouble.

The original sensor is so festooned with numbers, I was unable to get a part number on it until it was removed. Now, you have the part number.

When I got the valve out of the dashboard where I could play with it, I was able to diagnose that the valve was leaking through the stem. The knob is particularly annoying to remove because it was held in with a 1/8" driven pin. The replacement, a Haldex KN20021 -- again from NAPA -- has a nice spring loaded button on the valve stem instead of the driven pin. Thank you!! Note that removing the supply line will release the air from your air tanks. Before starting might be a good time to drain your tanks.

Re: Parking Brake Sensor Fixed

Reply #1 – August 15, 2020, 06:19:17 pm

Good reference material, Rick. Also, I gotta love the "festooned" you slipped in there. Thanks!
jor

Re: Parking Brake Sensor Fixed

Reply #2 – August 15, 2020, 10:01:04 pm

Quote from: trailertrashrick – August 15, 2020, 06:13:00 pm

The original sensor was a Hobbs S76578 normally closed 10psi switch. I replaced it with a Haldex BE13421 that I got from NAPA. The Haldex switch is physically bigger, but still fits. It's not the right switch and turns off at 66psi instead of the Hobbs at 10psi. Not really an issue in practice. You'll just get a Parking Brake light at the same time you get a low air light when you're in trouble.

Just a note in case you ever want to install the correct 10psi pressure rated switch, or in case another member has the same problem.

Working On My Six Pack

That pressure switch #76578-10 is the same switch I found (two of them) on my original factory HWH front 6-pack manifold. When I rebuilt my manifold, I replaced both switches with Stewart Warner part #76578. They were identical to the old switches in shape, size and function.

Only downside: They be kinda pricey.

Stewart Warner-Stewart Warner Hobbs Pressure Switch 10 PSI Normally Closed 2...

Re: Parking Brake Sensor Fixed

Reply #3 – August 17, 2020, 08:29:43 pm

My switch is 60 psi

Re: Parking Brake Sensor Fixed

Reply #4 – November 08, 2021, 04:38:03 pm

Digging this back up...has anyone seen the parking brake light on the dash stay on dimly when the brake is off? I just noticed this last night when parking from our latest trip. When the parking brake is set, the Park Brake light is bright like normal, but when the brake is released, I can still see the Park Brake indicator, at about 1/2 intensity. The DRL's do come on though.

Re: Parking Brake Sensor Fixed

Reply #5 – November 08, 2021, 04:48:55 pm

I replaced the sender at back of parking brake valve. It solved my problem. It was probably just a bad ground but I was replacing the valve anyway so I did the sender too.

jk

Re: Parking Brake Sensor Fixed

Reply #6 – November 09, 2021, 11:07:53 am

Keith,

It has been said here before, but when a 12 volt system is doing weird, illogical or unexplainable things, it is very likely a grounding problem.

Richard

Re: Parking Brake Sensor Fixed

Reply #7 – November 09, 2021, 11:24:01 am

Probably is. I went to inspect the issue last night and the issue was not present. Park brake light working as intended. Didn't find anything loose. Next time it acts up, I'll have to look at it right then.

Re: Parking Brake Sensor Fixed

Reply #8 – November 09, 2021, 05:36:07 pm

The dimly lit parking brake light gremlin is also residing in my dash. Usually it shows up when it's dark outside. Had FOT investigate a couple of years ago, but they couldn't locate the problem. His cousin gremlin the sporadic ABS light shows up unexpectedly, usually after I use the tag dump.

Re: Parking Brake Sensor Fixed

Reply #9 – November 09, 2021, 06:05:48 pm

Quote from: WagonWheels – November 09, 2021, 05:36:07 pm

The dimly lit parking brake light gremlin is also residing in my dash. Usually it shows up when it's dark outside. Had FOT investigate a couple of years ago, but they couldn't locate the problem. His cousin gremlin the sporadic ABS light shows up unexpectedly, usually after I use the tag dump.

That is the issue I saw Sunday night, but I could not replicate last night, at about the same time of the day. My ABS light was sporadic until my right front blowout, which ripped the ABS wire out from wherever it should go, and made it permanently on. I fixed that was some electrical tape over the light, as suggested by DSD.

Re: Parking Brake Sensor Fixed

Reply #10 – November 09, 2021, 07:26:29 pm

Wagon wheels the reason for abs light after a tag dump is because the tag wheels are not turning and the rest of the wheels are. Just have to put the tag back down and then turn off the key and then restart and when you start moving the abs light should go off.

Re: Parking Brake Sensor Fixed

Reply #11 – November 10, 2021, 11:59:23 am

I never noticed whether the ABS light was on when the tag was up. Usually I'm busy backing into a parking spot or driving thru tight corners in an RV park when I have the tag up. What I have experienced is the ABS light will be on the day of travel after I've used the tag dump. Other times while we are traveling I will pull into a rest stop for lunch and turn off the engine. After lunch I'll start the engine to resume our travel and low and behold the ABS light gremlin will make itself known. Next travel day no gremlin. Hopefully we'll never have a need for the ABS. Only had to break hard, but not enough to slide the tires, once in about 50K miles of driving.

Re: Parking Brake Sensor Fixed

Reply #12 – November 10, 2021, 12:33:53 pm

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Re: Parking Brake Sensor Fixed

Reply #13 – November 15, 2021, 05:12:38 pm

The dim park brake light was back last night. Since this is a normally closed switch, when closed it provides the ground for a bright light. When the brake is released, I assume the switch should open but is still providing some grounding, so I'm guessing this indicates an issue within the switch itself. Replacement from Napa in hand, will replace tonight.

Re: Parking Brake Sensor Fixed

Reply #14 – November 15, 2021, 09:25:22 pm

Well, the pressure switch is not in the dash from what I can see. Looks like there is an air feed line and output from the parking valve that exit through the hole in the floor. Any ideas where the switch might be in a 2003 U320? Of course it's dark an hour before I get home these days, so chasing black lines in the bundle of black lines, in the dark, isn't proving to be very easy.

Re: Parking Brake Sensor Fixed

Reply #15 – November 17, 2021, 09:17:19 pm

I called FT and tech support is looking for a diagram or schematic that shows me where this might be. Does anyone else have a clue?

Re: Parking Brake Sensor Fixed

Reply #16 – November 21, 2021, 05:36:14 pm

Turns out the switch is right on the switch, tight against the dash. Thing is, it is nothing like the switch trailertrashrich has. I'll start a new thread as it's a different item.

3-wire park brake switch

Re: Parking Brake Sensor Fixed

Reply #17 – November 23, 2021, 08:30:12 am

Quote from: trailertrashrick – August 15, 2020, 06:13:00 pm

This was a leftover from my Motorhomes of Texas visit. The parking brake dash light originally lit when I hit bumps, but got to where it would make a low level flash and you could hear a weak alarm sound pretty much all the time.

Since this came up recently, I thought I'd tell the rest of the story. Turned out the intermittent beep/flash was different from the sustained low level flash/beep. The sustained flash/beep was the sensor and it went away when I replaced it. The intermittent seemed to get better for a while, but came back. It was probably always there. This was frustrating because it had already been "solved".

The intermittent flash/beep turned out to be a bad ignition solenoid (Cole Hersee 24213). The major symptom of the bad ignition solenoid as it got worse was that the dash would reset (like when you turn the key on) and the engine would cut out.

My wife used to complain about all the Amazon boxes and all the spares I carry. Having the solenoid available on the road gave me some street cred at home. I probably don't need the extra filters, belts, air dryer bypass, air compressor governor, neoprene hose, air bag, and tire that I carry. But I might.

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Re: Parking Brake Sensor Fixed

Reply #18 – November 23, 2021, 09:06:08 am

Quote from: trailertrashrick – November 23, 2021, 08:30:12 am

1. The intermittent flash/beep turned out to be a bad ignition solenoid

2. I probably don't need the extra filters, belts, air dryer bypass, air compressor governor, neoprene hose, air bag, and tire that I carry. But I might.

1. Interesting. Haven't seen any other mention (on the Forum) of the 24213 solenoid failing. Something to keep an eye on... I use the 24213 for my AUX START solenoid (and Blue Sea 9012 for ignition solenoid).

2. I'm right there with you. I carry everything you do (except the spare air bag and tire) plus a collection of blade type fuses, air line fittings, several feet of PEX water pipe, assorted SharkBite fittings, light bulbs for headlights and tail lights, primary wire, and assorted wiring connectors.

"A part in the hand is worth two in the parts store (that is located 20+ miles away and closed on Sunday)".

Re: Parking Brake Sensor Fixed

Reply #19 – November 23, 2021, 09:34:34 am

Yes, the Blue Sea 9012 for ignition solenoid is a significant upgrade over the OE ignition solenoid.

It is the unit many of us upgraded to when our original failed.

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