Top speed 60mph

[Steve Dinkelman]

My 2008 Patriot Thunder will only go 60 mph. The speedometer is showing 75 mph. I have also lost my cruise control, and my jake brake.

The coach has a c15 engine. I also had the ECM replaced and I noticed the problem after that. Is the ECM flashed incorrectly or is it a speed sensor issue on the transmission?

[Steve Huber]

Steve,
A bit more info would be helpful?
What speed does  speedometer read?
What speed does digital readout display?
Do they read normally as the coach starts to gain speed and then "peg" at some point while the coach continues to gain speed?
Is the coach's actual speed being limited?

In any case it certainly sounds like the ECM may be at fault, especially since the issues didn't appear until after you had it replaced.
Steve

[Steve Dinkelman]

The speedometer shows 75mph and the rpms are around 1500. The transmission is shifting through all of the gears. I checked my speed with GPS and it showed me going 60mph with the speedometer showing 75mph.

[David Ciotti]

1500 RPM is high for 60 MPH.  At 60 MPH my 2002 Marquis with a C12 Cat engine shows around 1300 or 1400  RPM.

[Steve Huber]

At lower speeds do the GPS, speedometer, and digital display agree?

[Eric Maclean Co-Admin]

Steve
It appears the ECM programing is incorrect for your coach as all of your issues ( cruise control , Jake brake, and speedometer are all directly through the ECM
The fact that it all worked before the new ECM install points to a programming issue.

To confirm whether it's ECM or speed sensor related you need to check as Steve Huber suggests check your speed using the digital read out as it is reading what the engines ECM is receiving from the Allison transmission TCM .
Use that to compare with what the speedometer is reading and for a further check you can compare both to the GPS reading.

It's not uncommon for the speedometer to be out by 10%.
The speedometer receives a pulse signal which it converts to an analog drive for the gauge ,the same speedometer is used for several rear end ratios,
And each speedometer is calibrated using dip switches on the back to account for different rear end ratios and tire sizes.

How ever if no one has touched the speedometer or the transmission speed sensor the problem would point to the ECM you just had replaced.

For your cruise control and make brake make sure the coach brake light circuit is functional.

Hope this helps
Eric

[Scott Shearer]

Steve,

Please post a picture of your instrument cluster and front run bay (electrical compartment outside and below the driver’s window).

Your Patriot Thunder being 2008 model should have the Medallion digital instrument cluster. If so, all the gauges are digital and most receive information directly from the engine ECU via the J1939 circuit. If the ECU hasn’t been programmed to the correct specs the instrument cluster will not display accurate information.

Again, your Patriot Thunder being 2008 model could be equipped with the Kongsburg chassis multiplex controller (CCM). If that’s the case then almost everything in the cockpit area is controlled by the CCM, including the cruise control and Jake Brake.

There is some information on the Medallion Dash in Coast Assist.

-Scott