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Old 10-18-2021, 12:40 PM   #1
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Speedometer reads way too high and not shifting

I have had this happen to me three or four times in the past six months.
When first starting out on a drive, the speedometer would read way too high (like 80mph when I am only driving about 20), and the transmission not shifting.
What I did to resolve this issue was to pull over, turn the engine off, and then restart. The problem went away.
When I am underway without the speed increase and have no issue. I have a steady speed readout on my speedometer.
When I have the problem, I know right away.
I am concerned that one of these times I may not get so lucky.
Anyone have something similar happen?
Cummins 5.9L ISB 26 /275LT /300
and
Allison Transmission
Model 2000 MH
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Old 10-19-2021, 05:22 AM   #2
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What coach, year and chassis is this?
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Old 10-19-2021, 10:27 AM   #3
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2003 Holiday Rambler - Neptune

Was wondering if this may be the ECM, and if I should get it to a Cummins shop, or if I need to take it to my local truck repair shop
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Old 10-20-2021, 06:38 AM   #4
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I'm surprised that nobody has responded.
You may want to move or start a new thread on Monaco Owners forum. Maybe larger audience and better response.

I doubt Cummins would be able to help as it is the chassis or coach builder that incorporates all the stuff together.

Do you have wiring diagrams for your coach? You may be able to trace the source for the speedo signal as there have been many iterations over the years on those systems.
Sure sounds like a bad/intermittent connection somewhere. Just cleaning, tightening or moving any connectors in that system might clear your problem.
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Old 10-20-2021, 07:46 AM   #5
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I will move my post over to the Monaco forum
I am still tracking down electrical drawings to see what I can figure out.

I am trying to track down if it is perhaps an Allison Trans. or Cummings issue.
My speedometer is just an analog gauge.

When I have the problem my RMPs are low, so that is why I think it is my ECM on the engine. I believe the speed sensor goes into this, and the signal for the speedometer is sent out of this.


thanks
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Old 10-20-2021, 08:57 AM   #6
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Both my Speedometer and Tach get it's signals from the ECM based on my wiring diagram, I have a Cummins 8.3L ISC
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Old 10-21-2021, 06:11 AM   #7
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Same for the ISL.
The speedometer signal is the "VSS" (Vehicle Speed Sensor) from the ECM.

Do you have a data display device (like the ScanGauge D) that you can plug into the vehicle data port and monitor the speed signal? I use the ScanGaugeD on my Coach to display Speed, Engine Temp, Boost, and Trans Temp. You can select any four items to display at the same time. This is a more accurate way to monitor the engine than using the dash gauges.
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Old 10-21-2021, 08:47 AM   #8
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I use a Silverleaf display and can monitor as many items I can fit on the screen at one time. Right off the top of my head I monitor ~20 items and have alarms set up on at least 5 for high temps or low pressures and or voltage.
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Old 10-21-2021, 09:01 AM   #9
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I might look for a bad ground. It's a common fault for any type of electrical issue and your rig is getting to the age where it may become an issue. Good luck.
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Old 10-22-2021, 05:29 AM   #10
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I thought the VSS came out of the ECM (Eng. Cnt. Mod)as well, but if you look at the wiring I think it may come out of the TCM (Trans, Cnt. Mod.)

SEE ATTACHED IMAGES

The speed sensor is part of the Allison trans. and goes into the TCM.
Boy I am confused
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Old 10-22-2021, 08:57 AM   #11
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I had the circle of the VSS+ on the ECM on the wrong term
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Old 10-23-2021, 07:41 AM   #12
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The transmission speed sensor sends information to the ECM. The data also splits off and feeds your dash gauges.

Like in this diagram (which is from CAT service manual. But similar for Cummins):

I don't remember now how this thread got focused on the ECM. I'll bet your problem is with the transmission VSM. Do you have any fault codes?
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Old 10-23-2021, 03:47 PM   #13
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Quote:
Originally Posted by CountryB View Post
The transmission speed sensor sends information to the ECM. The data also splits off and feeds your dash gauges.

Like in this diagram (which is from CAT service manual. But similar for Cummins):

I don't remember now how this thread got focused on the ECM. I'll bet your problem is with the transmission VSM. Do you have any fault codes?

Yeah, these circuit diagrams can get confusing to the casual observer.
The ECM and TCM use many of the same signals for shift patterns, cruise, engine control, diagnostics etc.
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Old 10-24-2021, 06:33 AM   #14
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I don't know where I would read fault codes from, unless I had a diagnostic device. My dash is all analog
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