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Old 10-17-2021, 09:00 AM   #1
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1998 Monaco Dynasty Diagnostic Port - Check Engine - Overheat Water Temp Light

First let me thank anyone who replies to this thread. I have been searching to obtain more information on the Diagnostic Port capability of our 1998 Monaco Dynasty that has displayed a Check Engine light (Alarm Buzzer is no longer sounding) and a "Water Temperature Overheat" light on the dash board.

Since the engine has cooled down for over a week and the temp gage never went above 190 degrees, or the engine itself on any spot I shot with a infrared thermometer was not even 190 (hoses 177) when it was running I'm pretty sure this is a false reading.

I believe based on information I obtained from the forum that the sensor is in the back of the engine block and when it is unclipped the light remains on. There could be a bad wire but if the sensor works as it has been described removing it from the sensor would open the contacts and the light should go out.

There is 12 Pin plug under the dash to the right of the column marked diagnostic plug. I purchased an adapter (OBD1 to OBD2) and while it fits it does not allow my scanner to get power so that option to see information has failed.

The light came on during travel along with the alarm but went off after sitting in a camp ground for two days and travel of about 15 miles (better to say did not come back on when the key was turned to show a service person the symptom). It did not come back on again (no alarm - just lights) until after adding fuel 800 miles later when we were just 10 miles from the home base. It continues to stay lit during idle.

Would like to know if anyone has a good service manual link for this year and make motorhome. (1998 Monaco Dynasty)

Thanks again for any help that results out of this post.
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Old 10-17-2021, 09:39 AM   #2
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I do not know of any special service manual specific to a Monaco coach. The operators manual has some information but minimal technical data.

I would recommend creating an account on the Cummins Quickserve site.
https://quickserve.cummins.com/info/index.html
Once you create an account you put the SN of your engine in. This will allow you to access a lot of Cummins specific information including parts diagrams, maintenance manuals, service bulletins etc. There is also, at least on mine, a wiring diagram showing the Cummins to chassis interface.

On my coach I have a J plug on the left side of the steering column, this is a round 9 pin plug. I actually use a Silverleaf VMSpc monitoring system and it does have a diagnostic function that will show current fault codes and history. I can use the Quickserve site to look up the specific fault code which will provide troubleshooting suggestions/links.

I have a 8.3 ISC. I believe my engine has Cummins sensors but Monaco also installed separate sensor for engine temperature and oil pressure for the dash gauges. So it may be a sensor issue on the Cummins side even if the dash gauges show good.

Another potential cause could be the surge tank level sensor. The old sensor was known to cause a CEL, the sensor went down from the top about 2/3 the way down the tank. It was known to get a film on it causing false readings, you can remove and clean with a scotch brite pad.
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Old 10-22-2021, 11:37 AM   #3
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Following up on Jim J's comment.

I did subscribe to the free subscription and quickserve but that did not yield much help so far. It is just Free to look at what they will sell you and I'm not sure what I really need to buy. I would like to know what the $50.00 one week subscription gives you access to. If it was all access to manuals on-line mode only then it might be worth it. I was able to confirm that I have a Cummins C8.3 325 HP engine which I believe is NOT the same as a 8.3 ISL engine.

I've been putting all of my skills in the computer industry to work to understand OBD1 vs OBD2 and what that connector under the dash above the accelerator pedal provides.

I know that it has four pins. I know that the single pin is Ground and when I switch the key on the left pin measure 12Volts, the middle pin measures 5ish Volts and the right pin has 0-2 volts. This seems like it is a Serial Line datapath with power but that is as far as I've gotten. Don't know if it is a diagnostic for engine or just the transmission or both. Either way I suspect my Automotive OBD2 scanner would not have any of the data pre-programmed into it even if the interface could be wired up correctly. Hence the need for good documentation. Maybe that would be available for $50.00 for 1 week and I might pull that trigger.

I had some other things to fix anyway so I've been busy with them. Signal lights that were not working on the right side now have a new professional looking cable plant complete with a terminal block mounted on plywood. Who said it was a good ideal to bind all those wires into wire nuts? I bought some new light sockets but before they arrived I figured out how to make ground work on them again (2 of four were broken - hey it's a 1998).

Back to the Engine over temp condition. So until yesterday only the Check Engine and the Overheat light would come on but while working with the lights I started up the engine and now I have the alarm sound. If it follows the pattern I can drive it for a few miles turn off the engine and the condition will clear for another 800miles.

The engine is stone cold. No leaks detected, the coolant reservoir is at a good level, the fans are turning. What I believe to be the overheat sensor on the engine block does not have any impact if it is connected or disconnected.

I'll follow up when I have more to follow up with.
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Old 10-22-2021, 11:49 AM   #4
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I do not know when Cummins changed the Quickserve site to a subscription base site. Another poster had the same problem. Sorry about that, won't be recommending that people set up an account any more.

Your engine may not have the same diagnostics as miine, I had J type round plug on the left side of the steering column that I plug my Silverleaf into.

You might try contacting a shop and see what it would take to read the codes.

If you have the older surge tank the sensor is mounted on the top, it pushed into a heavy grommet. It is prone to getting a build up stuff on it and sends a false reading. You can try pulling the sensor and cleaning with a scotchbite pad. The sensor is obsolete.
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Old 10-22-2021, 12:27 PM   #5
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1998 was a transition year for Cummins from the mechanical injection C8.3L engine to the first electronic Cummins ISC 8.3.
First, we need to figure out which engine you have?

In my opinion you are wasting your time with that 12 pin connector.
Next, electronic diesel engines do not use automotive OBD 1 or 2, they use an SAE J1708 or J1939 diagnostic system. These are round 6 or 9 pin ports usually near the engine and under the dash.

We had an issue similar to yours with our 1997 Windsor. The radiator overflow/surge tank has an aluminum cylindrical sensor that screws into the top of the tank. It usually has a single wire attached but some were dual wire. This system is used with the plastic Volvo surge tank. Like Jim mentioned, new antifreeze has an additive that coats this aluminum sensor and causes a low coolant or engine temp red light.

The fix is fairly easy. Remove the aluminum sensor (which sometimes require dropping the tank) and clean it as well as the wire connector with some steel wool.

The bad news is this sensor cleaning will be required periodically depending on how long your coach sits.
I hope this fixes your issue.
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Old 10-23-2021, 11:00 AM   #6
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I'm 90% sure the exposed data plug you described is for trans only. I was searching for my data plugs and tracked it as labeled for trans. Its been a couple of years though. I have about the earliest electronic M11 never did find plug. I was considering Bluefire , but no one could tell me what info to expect ,the older the less info available.
Quote:
Originally Posted by SteveRVA View Post
Following up on Jim J's comment.

I did subscribe to the free subscription and quickserve but that did not yield much help so far. It is just Free to look at what they will sell you and I'm not sure what I really need to buy. I would like to know what the $50.00 one week subscription gives you access to. If it was all access to manuals on-line mode only then it might be worth it. I was able to confirm that I have a Cummins C8.3 325 HP engine which I believe is NOT the same as a 8.3 ISL engine.

I've been putting all of my skills in the computer industry to work to understand OBD1 vs OBD2 and what that connector under the dash above the accelerator pedal provides.

I know that it has four pins. I know that the single pin is Ground and when I switch the key on the left pin measure 12Volts, the middle pin measures 5ish Volts and the right pin has 0-2 volts. This seems like it is a Serial Line datapath with power but that is as far as I've gotten. Don't know if it is a diagnostic for engine or just the transmission or both. Either way I suspect my Automotive OBD2 scanner would not have any of the data pre-programmed into it even if the interface could be wired up correctly. Hence the need for good documentation. Maybe that would be available for $50.00 for 1 week and I might pull that trigger.

I had some other things to fix anyway so I've been busy with them. Signal lights that were not working on the right side now have a new professional looking cable plant complete with a terminal block mounted on plywood. Who said it was a good ideal to bind all those wires into wire nuts? I bought some new light sockets but before they arrived I figured out how to make ground work on them again (2 of four were broken - hey it's a 1998).

Back to the Engine over temp condition. So until yesterday only the Check Engine and the Overheat light would come on but while working with the lights I started up the engine and now I have the alarm sound. If it follows the pattern I can drive it for a few miles turn off the engine and the condition will clear for another 800miles.

The engine is stone cold. No leaks detected, the coolant reservoir is at a good level, the fans are turning. What I believe to be the overheat sensor on the engine block does not have any impact if it is connected or disconnected.

I'll follow up when I have more to follow up with.
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Old 11-11-2021, 10:41 AM   #7
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Still Searching ....

Still looking to resolve the issue with my CEL, MIL or what ever three letter acronym someone wants to call that Light on the dash that reads Check Engine along with Water Temperature Overheat light on. Since the RV has been stone cold for weeks now I'm sure there is a bad sensor. Thanks for the feedback so far I have made use of it all.

I did make some progress today with a new ICarSoft Heavy Duty Scanning tool to read all of the DTCs from the diagnostic connector shown in my picture above. Of course the scanner did not come with an ALDL connector (it looks like they have one on the side of the box as an accessory) so I just made the six pin J1708 adapter it came with happy with some alligator clips from the 1998 Monaco Dynasty Diagnostic ALDL connector just to the right of the steering column.

Figuring out that that plug uses the J1708 standard is worth another post. Short story is I found an image of the ALDL connector that matched my picture and it had J1708 beside it. That opened up a whole world of data about engine diagnostic connections. The nice thing about engine diagnostic standards is there are so many to choose from.

I had already exhausted all of the options for the OBD2 scanner that works great for OBD2 things.

On the J1708 plug that came with the IcarSoft tool I connected:
power from the ALDL to pin 5 of the J1708
Ground from the ALDL to pin 4 of the J1708
J1708 Signal High from the ALDL to pin 5 of the J1708
J1708 Signal Low from the ALDL to the pin 2 of the J1708

Turned the key on - Scrolled to Heavy Duty on the Icarsoft scanner and for the first time I got something out of the ALDL connector and was able to read all of the DTC codes that the tool would read. For every option it returned no DTC Codes Found.

Then I started the engine and had the scanner look at Live Data (LD) and it would run through a percentage count up (1 -100%) and say "No Supported Data Stream". I repeated the LD scan on every system (Engine, Console, Transmission, etc) that the tool has a function for.

If I disconnected either signal high or low the tool would provide the expected communications error.

So is the tool doing it's job? Seems like it is but no real way to know at this point and clearly Vito.a in the post above said I would be wasting my time with that plug and I'm out the time and he seems to be correct because I still have the CEL.

I did find a 1996 Dynasty wiring diagram this morning that shows what looks like a connection to a buzzer, overtemp light, ground, connection to the CEL, and connection to something label Coolant Tank Sending Unit which takes me back to the other point vito.a made in his reply. I see the sensor on top of the plastic surge tank but I was thinking that was the Low Cool sensor.

What I really desire is a complete wiring diagram like the one found while searching the web. That has a title of "Wire Diagram-Conventional, 12V MACK, 2013BP" and is 159 pages of details. If anyone wants to see an example of what I'm looking for. I would put the link here for that but there is a technical issue that blocks that right now.

I'm going to do some work with the tank Sensor and see if that is the issue. The buzzer no longer comes on but that might just have buzzed out.

I'm also left with the question of why Monaco put a CEL light on the panel if there was no way to clear the condition. If the CEL is wired into that Coolant Alarm then maybe I should just be searching for a bad ground or something. My diesel mechanic made that suggestion and he did not have the ALDL connector to check the codes either. He does not work on RV's but has done a few favors for me. He's thing is big trucks and just not configured to do RVs at his shop. He is my go to guy for anything diesel though.

Since I'm not close to a Monaco Dealer I'll keep searching for now and come up with a next steps plan of action. (Pump it with RV antifreeze and play with it all winter).

The search continues -
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Old 11-11-2021, 03:29 PM   #8
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Issue Solved - Check Engine and High Water Temp Light off

Four Letters -[Mod Edit] - and maybe persistence but the cause of the lights has been found.

First the wiring diagram - at this link below shows that the CEL is really just part of a type of analog computer that comes on when other lights on the dash come on. There is nothing about any ECM that turns that light on that I can see.

So for example the CEL light stays on until the air pressure builds up when you start the engine.

After my last post I walked away but could not stay away. Came back and kept digging. There is another post on irv2 where someone said they found the High Water Switch next to the transmission where the hot water hoses go to the font of the cab. So I go digging around looking for that and ultimately thought I found the block heater attachment - really just thought that was an option but in this process I found the 120Volt Plug that you can plug into the engine bay receptacles and keep the engine warm. They even talk about it in the paper copy of my 1998 owners manual. So I wanted to rule out what I was seeing to make sure it was not the other switch I was looking for and I pull out the manual. I'm flipping through it looking for that section on the heater when there staring me in the face is a picture labeled figure 3 Engine sending units (see attached picture). Yep right there all along since October 2nd when this issue first came up and long before that picture has been sitting right fricking there. [Mod Edit]. Labeled #1 High Water Temperature warning switch (HWTS).

The picture in the manual does not provide much context of where that switch is. They don't even reference figure 3 in the chapter or talk about it in the paragraphs before (This is 1998 long before everyone had Microsoft Word to do good documentation). My RV does not match the picture even but I found all four things in the picture and it confirmed everything I was thinking up to this point.

#1 There are two water temp gages on my RV. One on the Driver's console and one in the Engine Bay. That means there have to be two sending units or somehow they combined the temperature for two separate gages. Nope they did not combine anything right there in the picture and on my RV (under the bed access) there is this square metal adapter with a water hose connected to each end with the switch and two sending units one for each gage mounted on the top.

#2 The oil sending units are the same - They confirms two oil pressure gages one for the front one for the back.

#3 Again right there in the fricking manual are the letters C 8.3 Cummins. That confirms that I do have the mechanical Cummins 8.3 engine not the newer electronic fuel engine.


So first I ohmed out the HWTS and sure enough it was a dead short to ground. I disconnected the wire via the screw, turn the key and no HWTLight was on. Finally!!!!!!!

Then I tapped on that switch with the wrench while it was being toned out with the meter and the tone stopped. I hooked it back up turned the key and the light stayed out. I started the engine and it ran for maybe 60 seconds before it came back on. I think it is just a micro switch inside. I'll know for sure once it is replaced. For now I'm just leaving it disconnected because I know how to read a temp gage. It's not the part I been looking at on line (physical size is larger then I expected) so I'll still need to find a good part number for this. If anyone has that post a link in the reply. If I find it first I'll do the same.


Link to Wire Diagram

https://www.google.com/search?source...orwZzUi00SEj5M
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Old 11-12-2021, 09:37 AM   #9
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I was wondering if you might still have the C8.3 in your 1998 rig.

I'd consider myself fortunate (and do, since I also have C8.3).

It's funny, guys always talk about how the electronic engines are better, all the cool info they get to / have to monitor on their screens, and how they'd prefer air levelling vs having to deal with "unreliable" hydraulic jacks. But then you see a large majority of the problem threads in the forum are all about issues with the finicky electronic engines (mostly the fuel system to be fair) and air levelling systems.
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Old 11-14-2021, 05:31 PM   #10
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Simplicity is king

Agreed on the simplified aspect of not having a ton of electronic equipment associated with the engine. There is still a ton of electronic stuff on our 1998 RV. That diagnostic plug threw me because I kept thinking the way I think with the latest HPE Gen10 servers. Itís hard to think Windows 95 in a Windows 11 world.

I have a New Holland Skidster that is also 1998. Itís got two electrical circuits on it. A stater solenoid and Head lights. Feed it fuel and it moves through anything.

Back to this post if anyone has a part number for that water temperature switch in the picture I posted that sure would be helpful. I just want to fix it now.
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