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Old 08-03-2020, 09:27 AM   #1
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Join Date: May 2020
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2002 400 ISL goes to idle while driving?

We picked up a 2004 Safari Zanzibar with the 400 ISL / Allison 4000 earlier this year. It has a slight exhaust manifold leak but otherwise has run very well (I'll fix it over the winter).

We have put about 1,000 miles on it this summer and on two occasions while driving the gas pedal just goes dead and the engine goes to like a fast idle. The first time we were crossing some sketchy railroad tracks (slowly) the coach rocked quite a bit and it just went to a high idle (1200 rpms). I put the trans in N and shut it off. It started back up and was fine the rest of the way home. When I pulled the codes the ecm showed a (119 hydraulic pressure retarder & 55 shift finger status) and the trans showed 6600 for serial communications.

I checked for loose connections, reseated some connections underneath and zip tied some things and all was well for another 500 miles until yesterday.

Cruising though an Interstate construction zone the gas pedal went dead again (my stomach sank). It was smooth pavement cruising downhill and all the sudden nothing. Again I put the trans in N but I couldn't really safely stop on the Interstate. I slowed down to around 35 I think, shut the engine off, restarted and was fine the rest of the way home. This time the trans showed 6600 for serial communications again but no other codes.

Now I'm scared to drive it anywhere which is a shame because we obviously bought it travel.

I did find the can connection on the transmission not locked in last night (it was about 1/4 turn. So I took it apart cleaned it and screwed it back together until it clicked. I'm hoping this was the issue but not sure.

If anyone else has experienced this PLEASE let me know your experience.

Thank You!
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Old 08-03-2020, 10:07 AM   #2
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Not sure if you have the hi idle on your cruise control or not but if you do Maybe try turning cruise on / off and see if it comes back. It sounds like itís going to hi idle mode for some reason and at least on mine the pedal is dead until cruise is turned off and idle returns to normal.
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Old 08-03-2020, 10:11 AM   #3
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Call Cummins help line with your engine serial number and the codes. They are very supportive.
Gordon and Janet
Tour 42QD/InTech Stacker
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Old 08-04-2020, 12:11 PM   #4
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Location: Yellowknife, NT. Canada
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happened to me last year

Had the same thing happen to me on our first trip
Bad roads got us bouncing around and the throttle started to act funny and would go dead with no response. I finally hit a good bump and it went to idle only
Luckily I coasted to a pull over and spent the night. After some time on this forum I checked the TPS (Throttle position sensor) at the pedal. I guess my foot had hit it a couple of times on the big bumps and it was almost disconnected at the plug. I pushed it together and everything went back to normal. Used a wire tie to keep it away from my big feet and it has worked for over a year without issue.

Hope yours is as simple a fix
Dave and Carolyn W. With our dog Bear
Yellowknife NT Canada
2008 HR Endeavor 40 PDQ (Wild Horses)
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Old 08-05-2020, 08:41 AM   #5
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As Dave said it could be the TPS. First thing to try is to remove and reseat the connector; use some spray contact cleaner on the connection and retry.

If all that fails to solve the problem, there is a replacement throttle pedal assembly which uses a Hall-Effect sensor instead of the older rheostat type your coach probably has. That can be expensive, but a worthwhile alternative to getting a problem out on the highway. Below link is to a website which should be able to verify if that is the right pedal assembly for your coach.

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Old 08-06-2020, 07:52 AM   #6
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Thank You!

I've reseated the TPS connector.

I have a ScanD gauge set to monitor TPS while driving and I did notice the TPS was still fluctuating during the event. Now it may have sent an out of range moments before. Who knows.

I found some of the connections around the transmission not pushed together fully so I cleaned them, pushed them together and added a zip tie.

I also found the main ground at the engine/battery really crusty/rusty. So I took it apart, cleaned everything and put back together.

Not that I think about it - I should do the same to the ground up front.
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Old 08-23-2020, 05:12 PM   #7
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UPDATE: So it happened again today 💩💩💩.

Turns out it doesn't go to idle... the engine does shut off completely.

We were on backroads this time so we were able to safely pullover and restart. It continued home fine. Only a 17 mile trip.

I guess it was difficult to tell whether the engine was running over the road noise in the previous instances.
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Old 08-23-2020, 05:21 PM   #8
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Are you getting warning or check engine lights on at all?
2003 Monaco Windsor PST
Toad: 2008 Jeep Wrangler
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Old 08-24-2020, 08:20 AM   #9
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I havent noticed the dash check engine light come on but there were a couple of codes that showed on the ScanGauge.

119 hydraulic pressure retarder and 55 shift finger status

I think those are being caused by the shutoff though not causing it.

My buddy (a big rig tech) recommended changing the ignition switch so I'm going to change it as maybe something is cutting it off for a second.

However after researching last night - I may just be a newb owner as I suspect it could be the LOW COOLANT - STOP ENGINE event.

My rig doesnt have the dash light for the low coolant. Its there (printed on the wire) but no light for it.

Anyway I checked the coolant and it was just above the MIN level which is just above the sensor. I added 1.5 gallons of anti-freeze to get it to the MAX line. Luckily the previous owners left a gallon in a bay so I knew what to use.

It always seemed to occur when I would lift off the gas and was coasting downhill. They were also fairly rough roads in 2 of the events.

It sure is a pain to get the cap off and fill but I'm praying this fixes it!!!

I'm also going to change the oil pressure sending unit - in case that triggered the event.
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