Engine Speed (Revs) Increase when Coasting Down Hill at Highway Speeds (70MPH)

[Rosselk]

I am posting to the group on behalf of my son who owns a 2017 1500 4x4 with 170K miles. His issue is a little difficult to describe in words but I'll try.
When driving at highway speeds (interstate) and holding the throttle steady, he will occasionally notice that the engine speed (revs) slightly increase from 1800 to just under 3000 rpm when the truck is going down hill but he is not gaining speed. When he presses on the gas pedal slightly, the revs increase (and so does vehicle speed) but it feels like the transmission has shifted into the next lower gear (7th) and won't upshift to 8th. So imagine your cruising along at 70MPH with steady throttle applied and the road grade declines to a downward slope and without applying any more throttle, the engine speed increases. Yes his check engine light is on but the only code(s) retained per the dude at AutoZone was a loose gas cap.
So after replacing the gas cap I went for a ride with him and my observation was that the transmission upshifts and downshifts normally (quite smartly actually for 170K miles) with no latency between gears and at predictable speeds/conditions.
Has anyone else experienced such a drivability issue?
Thanks, Mike

 

[stevj]

Sounds normal to me.
Got lots of hills in my area so here are some things I've noticed with my Ram.
Taking the foot off gas pedal when going down hill: Firstly, the vehicle already knows you're headed down hill by the attitude sensor. Second, foot off the gas tells vehicle you want to slow down, so it will downshift to assist in that endeavor.
Put your foot back on the pedal and give it a bit of gas. Remember, the vehicle still senses down hill attitude so remains (usually, but not always) in a lower gear until level again.
Also, accelerating up hill will cause the transmission to stay in a lower gear longer (in my Ram until about 2400 RPM) before shifting to the next higher gear. Again, it's the attitude sensor at work.

Steve

 

[Rosselk]

Thanks Steve. Did you perhaps mean Altitude and spell check overwrote with attitude. I've never heard of such a sensor and neither has Google. Just trying to dive deeper into this issue.
"There is no official Mopar part called a "2017 Ram attitude sensor". The term "Attitude" refers to a popular aftermarket performance monitoring and tuning product called Juice with Attitude, made by Edge Products, designed for certain diesel Ram trucks."
Mike

 

[stevj]

Nope. Attitude.
The attitude sensor, or whatever Ram named it, is built into a module, typically attached to the floor under the center console on most vehicles.
This sensor provides nose up or down and tilt (or lean) left or right info, and turn rate, and feeds this data to stability control.
It is sometimes called a yaw rate sensor.

Steve

 

[Rosselk]

Steve, you might be onto something. Ram calls it the "multi-axis acceleration module" and Google's AI Overview reports this: Symptoms of a faulty 2017 Ram multi-axis acceleration module can include a "C006A-49" diagnostic trouble code (DTC), illuminated warning lights like the Malfunction Indicator Lamp (MIL) or Occupant Restraint Controller (ORC) faults, and inconsistent vehicle behavior. Inconsistent behavior can manifest as a delay or hesitation when accelerating, engine surging, or even the engine revving unexpectedly without pedal input. A related issue could be a U0150-00 code due to a loss of communication with the ORC, often caused by faulty wiring to the sensor.
Thanks again for the reply. You've given us a great starting point towards troubleshooting this issue. Mike

 

[John Kloehr]

... the only code(s) retained per the dude at AutoZone was a loose gas cap.

... Symptoms of a faulty 2017 Ram multi-axis acceleration module can include a "C006A-49" diagnostic trouble code (DTC) ...

The "AutoZone dude" code reader may not read all codes, particularly may not read chassis codes. If the truck has off-road pages, look to see it the angles look reasonable on the screen.

 

[Rosselk]

John, you're correct and I made a fundament assumption that all code readers are created equal. Is it reasonable to assume that if we had a dealer scan for fault codes that they could/would provide us with a detailed printed report? I don't intend to insult their intelligence by thinking I know more than them, but, I certainty don't want to throw dollars and time at this issue by replacing parts un-necessarily. This drivability issue will be impossible to duplicate and confirm a repair because the truck resides in Columbus, OH and only presents itself when my son travels home to northwest Virginia. If you've ever traveled on I-68 through WV and MD, you'd understand that this highway is like a roller coaster.
Mike