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TowDawg · 12-18-2021, 05:30 PM

I've got an interesting situation with my engine brake function on my 2002 HR Scepter with an ISC.

When the switch is turned on and I let off the throttle, the brake engages as it should. The problem is that when I get back on the throttle, it will not disengage unless I either come to a complete stop OR turn the switch off and physically tap the brakes.

I know one of the wires coming from the throttle sensor is what's supposed to send the signal, so I replaced the sensor and went on a short drive and viola, everything worked exactly as it should.

However, when I left for my last race, as soon as I got on the road, it was back to doing what it was before and I was thinking maybe I've got something sending a "spike" that's frying this part of the throttle sensor.
I found the "board" that the wires from the throttle sensor go to and didn't see anything wrong, but did notice that there are multiple other harnesses/fuses on the same board, with one of them being the lights.
That got me thinking about the fact that I always run with my lights on, but I don't think I had them on when I went for a short drive to test the function after installing the new sensor.
On the way home, I played with my theory and sure enough, if I have the lights on, the brake won't disengage with throttle input, but if the lights are off, the brake works exactly as it should.

Now with all that said, it certainly seems like there's some sort of "bleed off / interference" in that board when the lights are on. It can't be a fuse, so all I can think is that something in board has gone bad and is allowing signal interference across it somewhere.
Has anyone heard of this happening before?
I don't want to just keep throwing parts at it, but it's my best guess.

jacwjames · 12-18-2021, 05:47 PM

Not sure what might be going on.

But here is a wiring diagram for my 2002 Windsor but it also lists the Scepter on it. You can follow the wiring to see where there may be an interaction.

When you open the file it will be blurry, hit CTRL5 and it will clear right up. I zoom in to 1200% to be able see. Use the spy glass to search using key words, take a while getting use to what to search for but it works.

Keep us posted on your findings, you might say I have a vested interest in this since we have sister coaches.

TowDawg · 12-18-2021, 06:45 PM

Thanks Jim.

I know the fuse box/board I posted a pic of is the first place the wires form the lights and the brake interact with each other (the harness runs directly from the throttle sensor to this box/board), so it's my first place to start.
I just don't have much experience with these failing allowing the signals to "jump", but I can see the possibility of it.

jacwjames · 12-18-2021, 06:50 PM

I did a quick check of the wiring diagram and there are a number of places the signals could jump.

Any thought that it could be the VIP system??

There is an exhaust relay in the box, you may consider changing it.

153stars · 12-18-2021, 09:04 PM

Crazy issues like that always suspect grounding issue. I know that's not a lot of help tracking actual issue down. Sometimes just a second/ new ground helps . Things also change if component/item is switches on the ground side as well.

arcaguy · 12-18-2021, 09:12 PM

Yep my first guess would be a bad ground based on the age of the coach. The next guess would be a corroded connector somewhere causing a low voltage situation. It might not be easy to find as it will be an elimination of the possibilities situation. Good luck.

RealNiceTent · 12-18-2021, 09:45 PM

As a retired mechanic who specialized in electrical problems and diagnostics I will tell you the very first thing to check is power and grounds. You want to insure that you are receiving a full 13vdc to both the engine brake and lighting circuits, then you need to check voltage drop across the ground. Going from battery ground to the ground side of any point after the load should read 0.0v. If you read any voltage on the ground circuit you have a voltage drop across the ground or a bad ground.

In this case it sounds like the headlights share a common ground with the engine brake and there is high resistance at the ground causing a voltage drop that forces the engine brake to stay on until the load of the headlights is not present at the ground. Unfortunately the ground that is the offender could be in other locations like engine to chassis or body grounds, chassis to body grounds etc. Clean and tighten all of your battery grounds and check to make sure body, chassis and engine grounds are tight and clean. Then go for a quick drive and check the complaint, if the engine brake still refuses to shut off like it should, when it is "stuck on" turn the headlights off and on to see if the brake will release. Hopefully you won't have to perform this test. Even a lot of engine performance problems are actually power and grounds so it should be a starting point for most complaints.

TowDawg, side note here for you, the box you pictured is a relay center and they rarely contain circuit boards. They are almost always nothing but buss bars and connectors and very rarely cause problems or "bleedover". Chrysler minivans can be an exception, the main power center can become corroded internally due to their proximity to the battery.

TowDawg · 12-19-2021, 08:48 AM

Thanks everybody.

I'll have to find a friend who's more electrically inclined than I am and pass along the info.
I'm very mechanical and rebuild an engine with no problem, but start talking about measuring voltage drops form different places, resistance, etc and I go into a blank fog. lol

jacwjames · 12-19-2021, 08:56 AM

Monaco uses the same relay in a lot of applications. I carry a couple spares just in case.

https://www.ebay.com/itm/26538914982...temCondition=3
The fuse panel you show has one of these relays for the Exhaust Brake. I would try replacing it just to eliminate this as a potential cause.

I'll look at my DSFRB and see if I see any other potential causes.

wolfe10 · 12-19-2021, 08:57 AM

First, I would determine that this IS an electrical issue and not an exhaust brake that is hanging up.

What brand exhaust brake do you have?

jacwjames · 12-19-2021, 09:58 AM

Quote:

Originally Posted by wolfe10

First, I would determine that this IS an electrical issue and not an exhaust brake that is hanging up.

What brand exhaust brake do you have?

Yes, but I believe the relay I mention is the one that sends the signal to the exhaust brake On/OFF,

There are other interactions between power/ground throughout the electrical schematic but this one would be the first.

Alpine36 · 12-19-2021, 10:24 AM

In addition to all of the above make sure to add lubrication of the PacBrake to your maintenance schedule. Use the appropriate PacBrake lube.

bentjm · 12-19-2021, 12:49 PM

Pull the all the relays and check the connections for corrosion.

nehog · 12-19-2021, 01:33 PM

Quote:

Originally Posted by wolfe10

First, I would determine that this IS an electrical issue and not an exhaust brake that is hanging up.

What brand exhaust brake do you have?

I'm pretty sure he has a PAC brake... And if it is a PAC brake, then there is no feedback that the PAC brake is hanging up. The activate signal operates an air valve which in turn feeds an air cylinder to open/close the valve. The air cylinder is retracted with a spring, so that part is passive.

Quote:

Originally Posted by jacwjames

Monaco uses the same relay in a lot of applications. I carry a couple spares just in case.

The fuse panel you show has one of these relays for the Exhaust Brake. I would try replacing it just to eliminate this as a potential cause.

I personally strongly recommend against firing the parts cannon to try to fix things. Most times this simply results in a thinner wallet or bank account and not a fix. Proper diagnostics are a must in this situation.

OP: Put a meter across the throttle closed switch on the accelerator pedal and monitor the state of the switch. Make sure it opens/closes with activation. I don't think there is a PID but if there is you could monitor it with a Scanguage-D or other scan tool. Heck also check to make sure there are no codes. And another suggestion monitor throttle position with a scantool and make sure the throttle is actually returning to zero.