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Old 05-20-2021, 09:39 AM   #1
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Autopark system diagnosis

We have just had our third two in three years on the auto park system. The first two were a bad green switch and bad relay causing the system to lock up. This time we were leaving phoenix and headed up in the mountains of northern arizona for a two thousand mile trip through the national parks and on to Wisconsin for the summer. On a significant downgrade, the auto park light began flickering, it would come on flickering, then go off, then repeat. As we started the 6% upgrade, the light flickered again repeatedly and we began loosing power, RPMs declinling, coach slowing till we were down to 15 mph. I also began hearing some kind of faint screeching sound. When I pulled over and stopped the sound was louder. I shut off the engine, now heard a high pitched sound and determined it was the electric pump running wild on the auto park system. It kept running. After a few minutes I disconnected the electrical harness to the pump and it shut down.

My wife has high anxiety when we are broke down on the side of the road and I ordered a tow truck with our roadside assistance plan. While waiting, i reconnected the harness, the pump was silent, started the engine, put it in gear and the auto park system cycled normally releasing the brake. I could pull forward. Not wanting to have the likely same problem again with the mountains ahead we went ahead and got towed to Kingman AZ to a fairly large shop that does Auto/truck and RV's recommended by the tow driver. Monday AM when I spoke to the shop they couldn't replicate the problem. system was running normally. They had no previous experience with the auto park system and I referred them to my workhorse manual in the coach and the AutoPark parking brake system help, troubleshooting, and repair website which they consulted. They have checked the green switch for leaks, looked the hydraulic system over for leaks, and can find nothing wrong. I am not sure exactly what they have looked at, but no luck so far.

I have read the engine at highway speeds can overpower the brake if it gets applied underway. I theorize with the heavy tow load, coach loading and six percent grade, the brake was applied and with the combined loading overpowered the engine. I also understand the brake pad normally show no wear as they only lock the shaft normally, never stoping the coach. So, in the few minutes the brake was presumably applied I am hoping I didn't fry the pads. It seems to set up normally now.

As I understand the system, the actuator (spring and hydraulic actuator) is mounted inside the brake assembly on the drive shaft. That can leak but it is rare. To disassemble that component the shop says the coach has to go on the lift (apparently, they don't work under jacked coaches as many shops do) and it will be two days before the lift frees up and a couple hours more of labor. Is that true or is the actuator outside the brake assembly where it can be inspected for leaks? If so and it is not leaking the only reason to open the brake assembly would be to inspect the pads, and if the system seems to hold the coach with the brake applied now, it seems the pads are ok.

So, this is my sad tale of woe. Any of you had these symptoms, and what was the outcome? Any other ideas on diagnostics?

Thanks for your help.
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Old 05-20-2021, 10:25 AM   #2
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i would chock all wheels on flat ground.. ( hydro lift UP) then just look at a/p drum on back of trans.. ( use very good flashlight )see if dis-colored.. if it got hot.. then then a/p hydro res on pump see if has hydro oil.. 2 quick checks.. we need to know chassis yr and md to tell you where its at.. and look into a genie system for a/p. shop is correct.. never trust hydro lift.. always use jack stands or wood cribbing.. and chock wheels.. and safety helper with cell phone to watch and call for help.. if needed.. When last time changed a/p oil and flushed all chassis brake lines and greased caliper pins?? good luck and get back with us and let us know what happened.. there are great members here that will help..
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Old 05-20-2021, 11:42 AM   #3
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It’s an 04 holiday rambler P32 chassis J71 autopark system.
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Old 05-20-2021, 12:03 PM   #4
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Is the fluid level in the reserve tank full?
The actuator is underneath the chassis about in line with the rear of the transmission housing. Check in that area for a sign of a fluid leak if the tank isn't completely full.
I always carry a spare pair of switches with me just in case. I recently bought and installed the two lifetime switches offered by Ultra RV Products (www.urvp.com) but I will take the relatively new switches I removed along for the reassurance or to help someone else out if I ran into the situation where it would.
The fact the A P lamp was flickering leads me to believe it's this system which is your problem as the A P and the foot pedal braking systems are totally independent of each other.
If the shop has questions they could call Ultra 7 AM-4 PM PST for assistance and parts availability. 800-417-4559 Mon-FRI They are located in Washington State but ship out fast.
Look into the Lifetime switches for peace of mind.
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Old 05-20-2021, 02:10 PM   #5
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The auto park atf tank is full to normal levels. They checked for leaks but I haven’t verified they checked the actuator specifically I will.
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Old 05-20-2021, 02:33 PM   #6
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If nothing else I would replace the switches. Diagnosing any system which is working as it should is not only difficult, it's impossible. We may just have to go with our best guess. If the switches aren't readily available I'd recommend the lifetime switches from Ultra RV. Not a lot more money than the standard switches but should cure any switch problem you could have in the future.
I'm in Northern NY (State) and received mine in two days from Ultra.
There is another thread going right now in the "Vintage RV" room about A P with a Gentleman from Germany who folks on this forum have been helping. I have part numbers listed in one of my posts. Join in if you wish.
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Old 05-20-2021, 11:00 PM   #7
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If you find no visible leaks and you have changed the RGS (Parking Brake Motor Switch) you might check the Parking Brake Solenoid Valve. This is the solenoid valve mounted on the pump assembly block. It could be cycling. If so, this means the valve is opening, dumping the fluid back into the tank and allowing the light to come on and thus energizing the pump assembly. If this valve closes again, it will allow pressure to rebuild and turn the light off again shut down the pump. A very likely suspect, if no visible leaks are detected.


Call Ultra RV and ask for Allen, he is their expert on Auto Park Brake System. Have your VIN ready so he can look up your build sheet. It should tell him what pump system you have installed. It make a big difference. Several pump manufactures where used by Workhorse.


As stated earlier, they have some excellent replacement switches that will get rid of the old pump motor switches (green or brown) and system pressure switch (grey).
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Old 05-29-2021, 06:33 PM   #8
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I installed the 3 light genie on our autopark and would get an occasional yellow light for about 1 sec. indicating the pump running and then it would go back out, it would stop after several cycles and wouldn't do it again until the next day. I rebuilt the actuator cylinder which was leaking, it still did it. I replaced both switches with the Ultra RV lifetime units, still did it. Then I replaced the solenoid unit and pump check valve and have never had it happen again through thousands of miles of driving. If you don't have the Genie 3 light warning system installed, it's a cheap upgrade that can be a life saver, do a search here, plenty of info about it.
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Old 05-29-2021, 06:47 PM   #9
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Making the assumption that you did not loose all your fluid, then it seems most likely your problem is either a bad green switch, a bad relay, or possibly it was cycling repeatedly due to check valve leaking and you did not notice it until the electric pump motor shut down on overheat, at which point it leaked down and the brakes locked up. (it seems most of the time these motors will burn instead of shutdown on overheat thermal protection, so you may have got lucky here).


If the problem were in the actuator or lines you would have a puddle of fluid and your fluid reservoir would be low / empty. (note you need to take the cap off to check fluid level, you can't tell by looking at least not on mine as the fluid has stained the reservoir and makes it look full from the outside even when empty.
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Old 05-30-2021, 08:48 AM   #10
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Update and additional question

So here is the update. We decided to abandon ship for the summer, put the coach in storage in Kingman, load as much of our gear as possible in the car and catch up with our friends and then head to Wisconsin and our cottage without the RV. After three auto par failure tows, and concern about the quality of the work I could get done in Kingman and the time involved to sort this all out, we gave up for now.

Here is what I learned in addition to all the good info from response to my post. First the owner of the shop said he personally reviewed the work of his tech and took the unit out for a test drive. They found no leaks including through the RGS. He “warmed it up good” and DT the brake up and down a good hill. The brake operated normally and held on grade. So he couldn’t find a problem. Not what you want to hear.

One of the posts referred me to Allen at Ultra Products. After talking to him I do believe he is an expert. He was pretty sure the problem lies in the relay/coil/solenoid assembly on the auto park brake assembly. Something like too much current starting to kill one of those components causing when good and hot the solenoid to cycle such that the fluid just goes back in the reservoir and not to the actuator thus the spring actuated the brake. He says it will happen again. He was quite sure the problem lies on those three components.

Further he said the workhorse pump assembly is no longer available nor are the individual solenoid, coil, relay. He also said due to age, the actuator will leak at some point. As you may know Ultra has engineered a pump assembly replacement ($1700) including the two lifetime switch’s to replace the green and gray switches, and an actuator assembly for about $500. This isn’t about the money for me. I have to truly improve the reliability of the auto park system if I am going to keep the coach. Three tows is insane. Have any of you had experience with the Ultra pump and actuator assemblies and have they proven reliable?

He also said it might be possible to source a general purpose solenoid/coil/relay and replace those components. My parts guy at my shop back home also said that might be possible. Has anyone out there done that and can give me a source reference?

Right now I am considering getting a buddy to go with me, disconnect the brake, head four hours back to Phoenix in the fall (three long 6% grades) and then get my shop to install the Ultra pump and actuator including the two critical switches and install the genie light system and essentially have all new critical components better diagnostics and hopefully a more reliable system.

Any other thoughts on all this?
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Old 05-30-2021, 10:25 AM   #11
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You may already know this but,

If you disconnect the AP you will not have any way to keep the coach from rolling without chocking the wheels.
The transmission does not have the Parking Pawl in it. So the transmission in Park is the same as in Neutral.

Just something to be aware of.
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Old 05-30-2021, 01:23 PM   #12
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if you have a foot pedal for the brake (aka emergency brake).. .. use that every time you put in park.. and still chock wheels.. pick you up good set of chocks at big box stores.. get atleast 8.. and use every ting you get out.. better yet have some one do it while you hold brake.. unless you have foot pedal.. as above.. warning.. this is not like a car.. there is no device in trans to stop mh from rolling and killing some one.. now if you feel comfortable you can find parts cheaper on ebay and amazon.. but the sponsor you used has a high reputation.. i added an alarm buzzer to mine and it will wake up the dead.. there is a post if you are willing to put time in it .. that a person here put a hyro seal in for 2.00 and did it himself in about 1hr.. you can rebuild the acutator for 2.00 from a hydo seal comp..its all up to your wallet.. just letting you know.. and when is last time you changed relay and really.. really.. cleaned the connections???? i got my relay at another place 70amp hd way cheaper.. you should not just though parts.. but for sure you will have a new beutifull job when done.. good luck.. post picks.. we always try to hinder if poss...
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Old 05-30-2021, 02:24 PM   #13
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I have the Ultra RV Products pressure switches on mine, I installed them in the spring of 2019 after my gray stop switch failed and dumped all the fluid on the floor of my storage shed. It failed 300+ miles from home, but was not leaking, it had just set the light, the rotten green switch was still functional, so I drove it home, made it home fine, no sign of leak, then on about the 3rd day after I got home it dumped all the fluid on the floor of the shed overnight. No issues with the switches since then, though I did have a fluid leak at a splice fitting that I had to tighten up this year, 3-4 years ago I had a pin hole leak in a radius bend of the original hardline, so had a local shop fabricate new line from the pump up front under the hood back to the actuator.
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Old 05-30-2021, 07:29 PM   #14
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Safety warning on auto park disconnect

I am very aware if I disconnect the park brake to drive home I will have no way to keep the coach from rolling when stopped other than the vehicle brakes and chocking the wheels. I have the J71 third series from 2004 which has no foot pedal. I will have a buddy along if I go that route and will get some big as..... cocks for all wheels. Thanks for the warnings.
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