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Technical Support / Re: Engine Shutdown While Driving
« Last post by Bill Heffernan on Today at 02:49:00 PM »Thanks Scott. We are moving again later today, I'll be watching for it.
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Technical Support / Re: Engine Shutdown While Driving
« Last post by Scott Shearer on Today at 10:01:00 AM »Bill,
Seeing zero boost would be expected, the engine sensors have lost power because the 12-volt switched ignition power to the engine ECM has been lost (loss of engine comm).
Our 2006 PT does not have the Medallion Digital instrument panel or the Light Bar like your coach, but I am running the Silverleaf VMSpc. Both the Medallion Digital system and the Silverleaf receive their information from the same source, so it should be a reasonable comparison.
When our engine shutdown the speedometer, tachometer and transmission gear attained were all registering data. I could see the transmission shifting down until I selected neutral. I did see the oil pressure light turn red and the oil pressure gauge go to zero (a bit alarming).
Suggestion, when you go back on the road run with your Aladdin system engine/transmission data screen displayed. If all engine data goes to zeroes during a shutdown, you’ll know that the 12-volt switch ignition power has been lost, the Aladdin system requires it to display any engine data.
-Scott
Seeing zero boost would be expected, the engine sensors have lost power because the 12-volt switched ignition power to the engine ECM has been lost (loss of engine comm).
Our 2006 PT does not have the Medallion Digital instrument panel or the Light Bar like your coach, but I am running the Silverleaf VMSpc. Both the Medallion Digital system and the Silverleaf receive their information from the same source, so it should be a reasonable comparison.
When our engine shutdown the speedometer, tachometer and transmission gear attained were all registering data. I could see the transmission shifting down until I selected neutral. I did see the oil pressure light turn red and the oil pressure gauge go to zero (a bit alarming).
Suggestion, when you go back on the road run with your Aladdin system engine/transmission data screen displayed. If all engine data goes to zeroes during a shutdown, you’ll know that the 12-volt switch ignition power has been lost, the Aladdin system requires it to display any engine data.
-Scott
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Technical Support / Re: Engine Shutdown While Driving
« Last post by Bill Heffernan on Today at 03:44:56 AM »Thank you everyone for the recommendations and insights. The mechanic went through most of the recommendations, he found a number of corroded connections, including grounds, which he cleaned up. After a bunch of starts and stops (shutdowns)(pun intended) he finally got it to run for an hour with no issues. Of note, the dash would show a lost engine comm message after every shutdown, but when he pulled codes, it would disappear. We got back on the road and within miles we had another loss of power event. I was a bit more observant this time. We lost power, turbo boost went to 0, but the engine RPMs stayed up (I had not observed this previously.) This occurred about 3 times within 3 miles, each time within around 10 seconds we re-gained power and turbo boost. After those three "burps" everything ran great for the remaining 2 hours of our trip. These incidents felt very similar to what I have felt previously when this started, sometimes recovering like today, other times shutting down. In the repair yard it would simply shutdown without warning. Also of note, for the last three segments of our trip where we've had this issue, it seems to happen within the first 20-25 minutes of the trip and then runs fine. The mystery continues.
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Technical Support / Re: Engine Shutdown While Driving
« Last post by Scott Shearer on September 30, 2026, 04:23:28 PM »Fred,
Thank you for sharing the YouTube reference. The video was informative.
Watching the video, one might think it necessary to remove the rear start PCB prior to the installing the jumper wire, it is not. As an alternative way to shut down the engine while using a jumper is to turn off the chassis battery disconnect, then remove the fuse.
Very important!!
Jumpering the start solenoid as shown in the video bypasses all safety interlocks, including the neutral-start safety. Before proceeding, verify that the transmission is in neutral. Chocking the wheels is also recommended.
-Scott
Thank you for sharing the YouTube reference. The video was informative.
Watching the video, one might think it necessary to remove the rear start PCB prior to the installing the jumper wire, it is not. As an alternative way to shut down the engine while using a jumper is to turn off the chassis battery disconnect, then remove the fuse.
Very important!!
Jumpering the start solenoid as shown in the video bypasses all safety interlocks, including the neutral-start safety. Before proceeding, verify that the transmission is in neutral. Chocking the wheels is also recommended.
-Scott
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Technical Support / Re: Engine Shutdown While Driving
« Last post by Fred Cook on September 29, 2026, 01:26:35 PM »Thanks Fred. Yes, we were able to re-start. We found a local mechanic. He went through all the electronics and did not find any issues. He pulled and checked fuel filters - one of them looked a bit rough he said, replaced them and checked fuel pressure, again no problems. After that it ran fine for about 20 miles, when we lost power briefly, but it did not shutdown. We kept going for anther 150 miles with no issues. At this stage it appears that it was a fuel/fuel filter issue. We are back on the road tomorrow. Hopefully no more issues.
Bill, from what you are describing I had the same exact problem…. Motor dying sporadically while at idle and while driving down the road. And… after dying it would restart when turning the key on again. Your problem is in the rear run box on your ignition board. Your likely culprit is the relay on that board which cost about $10 off Amazon. That relay is soldered on to the board. I pulled my board off and took it to a circuit board repair shop near my home. They cleaned the board up and soldered the new relay on. It’s been about a year and haven’t had a problem since…. Knock on wood. In the meantime there is a temporary fix as Scot described above to stay on the road. Get on YouTube and search Cummins ISL 400 ENGINE COMM ERROR. Although that guy has a Cummins, the run board is similar to a CAT.
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Technical Support / Re: Engine Shutdown While Driving
« Last post by Eric Maclean Co-Admin on September 28, 2026, 12:48:30 PM »Scott
Your last post is very detailed and could be very helpful to anyone will similar coaches and problems on the road
Thank you for your input.
Eric
Your last post is very detailed and could be very helpful to anyone will similar coaches and problems on the road
Thank you for your input.
Eric
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Technical Support / Re: Engine Shutdown While Driving
« Last post by Scott Shearer on September 28, 2026, 11:46:04 AM »Bill,
It’s unlikely that either a “low battery” message or a “loss of engine comm” message would be caused by fuel filters. A “loss of engine comm” message usually indicates that the engine ECM is not communicating with the coach systems.
If this happens again, there are a couple of things you can check to determine whether you’re dealing with an electrical issue.
First, if you have a functioning Aladdin system that displays engine/transmission data, turn the ignition key to the run position and check whether the engine/transmission page shows all zeroes for the engine data. All zeroes would indicate that the engine ECM is not transmitting engine data.
Next, open the rear run box. Again, with the ignition key in the run position, look at circuit boards #1 and #7 (they are marked PCB1 & PCB7).
On PCB7, all LEDs should be illuminated red; fuses 1, 2, and 3 provide power to the engine ECM.
On PCB1, the rear start PCB, LEDs D1, D2, D3, D5, and D8 should all be illuminated.
LED D1 should be green.
LED D2 should be yellow.
LED D3 should be red.
LED D5 should be yellow.
LED D8 should be red.
If LEDs D1, D2, and D3 are not illuminated, you do not have ignition power at the circuit board or to the engine ECM. This will defuel the engine and shut it down. Check the 5-amp fuse on PCB1 labeled IGN FUSE.
The following two conditions are probably not roadside repairs:
If LEDs D2 and D3 are illuminated but D1 is not, the ignition relay is probably bad.
If only LED D3 is illuminated, further diagnosis will likely be needed.
There are a number of possible failure points in the ignition system on this era of coach, but a common problem is the ignition circuit board in the rear run box, PCB1, or one of its components, as Fred mentioned.
EDIT***
Also, avoid hanging extra keys from the ignition key. These Monaco coaches use an older style GM ignition switch and don’t like having extra weight hanging on them.
You can use a simple fused jumper wire to temporarily bypass the entire coach ignition run circuit. This can at least get you to a safe place. After experiencing an uncommanded engine shutdown with no restart, I won’t leave home without the jumper. My shutdown was on a busy two-lane Oregon coastal road with no shoulder—was not fun.
I’ve included the following images:
PCB#1 with correct LEDs illuminated when the ignition key in the run position.
Ignition bypass jumper.
Ignition bypass connection locations.
-Scott
It’s unlikely that either a “low battery” message or a “loss of engine comm” message would be caused by fuel filters. A “loss of engine comm” message usually indicates that the engine ECM is not communicating with the coach systems.
If this happens again, there are a couple of things you can check to determine whether you’re dealing with an electrical issue.
First, if you have a functioning Aladdin system that displays engine/transmission data, turn the ignition key to the run position and check whether the engine/transmission page shows all zeroes for the engine data. All zeroes would indicate that the engine ECM is not transmitting engine data.
Next, open the rear run box. Again, with the ignition key in the run position, look at circuit boards #1 and #7 (they are marked PCB1 & PCB7).
On PCB7, all LEDs should be illuminated red; fuses 1, 2, and 3 provide power to the engine ECM.
On PCB1, the rear start PCB, LEDs D1, D2, D3, D5, and D8 should all be illuminated.
LED D1 should be green.
LED D2 should be yellow.
LED D3 should be red.
LED D5 should be yellow.
LED D8 should be red.
If LEDs D1, D2, and D3 are not illuminated, you do not have ignition power at the circuit board or to the engine ECM. This will defuel the engine and shut it down. Check the 5-amp fuse on PCB1 labeled IGN FUSE.
The following two conditions are probably not roadside repairs:
If LEDs D2 and D3 are illuminated but D1 is not, the ignition relay is probably bad.
If only LED D3 is illuminated, further diagnosis will likely be needed.
There are a number of possible failure points in the ignition system on this era of coach, but a common problem is the ignition circuit board in the rear run box, PCB1, or one of its components, as Fred mentioned.
EDIT***
Also, avoid hanging extra keys from the ignition key. These Monaco coaches use an older style GM ignition switch and don’t like having extra weight hanging on them.
You can use a simple fused jumper wire to temporarily bypass the entire coach ignition run circuit. This can at least get you to a safe place. After experiencing an uncommanded engine shutdown with no restart, I won’t leave home without the jumper. My shutdown was on a busy two-lane Oregon coastal road with no shoulder—was not fun.
I’ve included the following images:
PCB#1 with correct LEDs illuminated when the ignition key in the run position.
Ignition bypass jumper.
Ignition bypass connection locations.
-Scott
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Technical Support / Re: Engine Shutdown While Driving
« Last post by Bill Heffernan on September 28, 2026, 01:36:07 AM »Thanks Fred. Yes, we were able to re-start. We found a local mechanic. He went through all the electronics and did not find any issues. He pulled and checked fuel filters - one of them looked a bit rough he said, replaced them and checked fuel pressure, again no problems. After that it ran fine for about 20 miles, when we lost power briefly, but it did not shutdown. We kept going for anther 150 miles with no issues. At this stage it appears that it was a fuel/fuel filter issue. We are back on the road tomorrow. Hopefully no more issues.
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Technical Support / Re: 2001 Beaver Marquis. Transmission selector not working
« Last post by Vernon Boen on September 27, 2026, 04:09:52 PM »Still needing some help....,I replaced the 2 chassis batteries. One of them tested weak and they were 7 years old so I figured just replace and save some hassle later. I also know Allison transmission are very dependent on constant voltage so I wanted to eliminate voltage issues. As I stated before the coach will start at the rear start button in engine bay and I happened to notice the brake lights were on when I turn the key switch on. The lights I have on the dash are check transmission and engine brake applied. I'm assuming something between the two are responsible for the transmission pad not lighting up. I checked the jake brake switch and it is in the off position. I also turned the jake brake on and accelerated the engine and the jake brake engaged when I release throttle. So I know the jake brake switch it ok and the jake brake is performing properly. It also has a different light on the dash that comes on when jake brake is turned an goes out when its turned off aside from the one that is staying on all the time with check transmission light. Ive also checked the brake light switch and it is good. I have also checked all relays and replaced every fuse. Any ideas?
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For Sale, Rent or Wanted by Beaver Owners / Re: Wanted 2001,2002 beaver Marquis Emerald edition
« Last post by Dane James on September 26, 2026, 03:04:32 PM »Found your link, more than I want to spend, nice looking coach.