Primary Air Gauge Malfunction/ Reading

[markletheridge]

I have a 2008 Fleetwood Discovery 40x, Freightliner Chasis. During trip back from Indiana, the air pressure reading in the primary gauge started acting up, going from 110 or so which is normal to close to zero, back and forth quick and the low pressure alarm came on. Much to quick for a real pressure change. This seemed to be triggered by rough road conditions. Pulled of, turned coah off and back on an ok until next rough road. The book says that parking brake will engage at less than 38-42 psi. Freightliner service says that will not happen unless the real pressure is that low, that a faulty reading won't cause it. Don't want to be driving and have the parking brake engage. 

Any ideas on how I can deal with this myself, Freightliner is backed up for over a week and says that all they can do is change parts if it is anything electrical.

 

[desertdeals69]

Look at the 1/4 inch lines coming from each tank to a manifold near the steering and see if there is any loose or cracked connections.  The low pressure warning sender is on a manifold in that area.  I think the tubing is yellow.

[jleamont]

6 hours ago, markletheridge said:

I have a 2008 Fleetwood Discovery 40x, Freightliner Chasis. During trip back from Indiana, the air pressure reading in the primary gauge started acting up, going from 110 or so which is normal to close to zero, back and forth quick and the low pressure alarm came on. Much to quick for a real pressure change. This seemed to be triggered by rough road conditions. Pulled of, turned coah off and back on an ok until next rough road. The book says that parking brake will engage at less than 38-42 psi. Freightliner service says that will not happen unless the real pressure is that low, that a faulty reading won't cause it. Don't want to be driving and have the parking brake engage. 

Any ideas on how I can deal with this myself, Freightliner is backed up for over a week and says that all they can do is change parts if it is anything electrical.

 

Freightliner is be dropping the ball lately on their tech line or playing possum. I have heard of this happening on a few RV's and its very common on the M2 truck with is similar to the RV chassis, but with the engine in the front (lots of shared components). That and the wipers coming on by themselves along with hazard lights and heater fan is also VERY common on the truck line.

If it went to Zero, it wasn't an air leak or you would have come to a fast stop when the parking brake applied. My bet, another computer blunder or sending unit problem. Try and see where the gauges get their signal, start with checking the electrical connection for corrosion.  

[dickandlois]

markletheridge

DD's Coach is a little older then yours and his coach will have gauges that read air pressure directly, but the newer models have a module that converts air pressure to a voltage level - that  is connected to the Air pressure gauges.

If you find wires connected to the pressure gauges and with the pressure levels jumping around. The best bet is an issue in the module.  Common issue is bad / cold solder joints in the area of the signal / voltage output. 

The other possibility is a corroded or loose data connection at the module. 

If the air pressure was indeed dropping  below a level controlled by a PPV an alarm would sound !! 

Let the group know what you find behind the dash!

Rich.

[markletheridge]

thanks for the info. i will let everyone know what we find.

[elkhartjim]

Its a known problem with the connections on the daisy chain wiring. There is a recall to replace the wiring. I had the same issue on my 2008 bounder Diesel. They mailed me the wiring harness and I replaced the existing harness with never another issue. 

Have you called the help desk?

[desertdeals69]

On 8/29/2017 at 10:39 AM, DickandLois said:

markletheridge

DD's Coach is a little older then yours and his coach will have gauges that read air pressure directly, but the newer models have a module that converts air pressure to a voltage level - that  is connected to the Air pressure gauges.

If you find wires connected to the pressure gauges and with the pressure levels jumping around. The best bet is an issue in the module.  Common issue is bad / cold solder joints in the area of the signal / voltage output. 

The other possibility is a corroded or loose data connection at the module. 

If the air pressure was indeed dropping  below a level controlled by a PPV an alarm would sound !! 

Let the group know what you find behind the dash!

Rich.

My misunderstanding.  I toured Freightliner in Gaffney a few weeks ago and they were talking about the fewer wires in the harnesses on current coaches because of the new design.  I think they called it multiplexing.  They talked like it was rather new so I didn't think it would apply to a 9 year old coach.

[jleamont]

Multiplexing; engineers love it, mechanics and end users hate it. 

[dickandlois]

9 hours ago, jleamont said:

Multiplexing; engineers love it, mechanics and end users hate it. 

Joe- CAN network, it saves a lot of wire, but it is a pain in the backside. If they are going to use it they should print all the code errors in the owners manuals. Custom Chassis have items installed in them that are not common in the Big Rigs an many of there service centers do not have a clue of how a CAN system works IMHO !

Second issue is Freightliner is at a point where a bigger number of there employees are at or near retirement age.  

Rich.

[manholt]

Rich.  Retirement in a big major company, is like a bank of elevators...as it goes up, others get on the bottom floor.  Bad training=bad or misinformed tech's!  I would give a call to REV tech department.

[jleamont]

Rich, I agree it does save a bunch of wiring, but no one had this many problems until it came into the industry, gauges connected directly to the source proved reliable for many, many years. Now I have tractors with the Engine light on because the CD player jammed up . Just had a new tractor the other day, we pulled the radio out for repair, truck wouldn't start , had to drop the drive shaft to tow it out into the lot , remember this all started with a radio problem.

The money spent now a days to keep this stuff on the road is insane, common sense and reliability went out the door, now we throw money, lots of money at it to keep it on the road, meanwhile our older tractors are up over 1 million miles with minor problems occurring that you would expect and can figure into the equation. the reps come in to sell more equipment, all I hear is what the next gadget will do, in my mind; oh great, that will be several more breakdowns.

[dickandlois]

Ditto - Joe. I'd Bet money that there is a 5 volt circuit(s) in the cab dash area - that sends a code to the ECM and any and all codes in that module offer a check engine code.

One is allowed 1 code in the ECM, but if you have 2 codes stored the light comes on. 

Just need to play there game or play hard ball. Maybe they need to be called to court and made responsible to cover down time cost for any and all items that stop vehicles not directly connected to the drive train. 

See there is a thread involving an up date from Mercedes to have a software up date installed and once it is installed the check engine lite stays on and no one is taking any responsibility - sounds like the issue is going in circles. 

Personally feel that the person writing the program update never left their desk and went to the garage to see what happened when it was installed. Just run the program on a computer and it did not error out - so the code string had to be correct. Not My Problem Issue.

Kind of like the new systems that prevent the cell phone from working if a vehicle is moving more then 3 to 5 MPH. 

Rich.