Rough Road Detection "feature"

[Keith Armstrong]

I'm having trouble keeping the check engine light off on our recently acquired '97 D90 SW.

The dealer replaced the RRD ecu under the seat before we got it, and subsequent problems led them to believe that they needed a software upgrade.

They had the vehicle most of the day yesterday and the tech said that he followed the LRNA proceedure for the upgrade without success.

He cleared the codes - RRD only - and gave it back to me with the light out.

A short blast up the freeway entrance ramp, over a little bump, loose traction for a split second, yup - light's back on

Where the heck is the sensor for this thing? On the wheel, on the crank?

Not particularly worried, but kinda tired of looking at the cute red light on the dash

Thx,

KAA

[darkstar]

The RRD system uses the ABS wheel sensors. If the air gap is wrong, or the sensors have gone bad, your CE light will come on. Fun, eh?

[redrangie]

wtf is a "rough road detector" Is that so you don't spill your coffee? wow... I put up a post needing help about dimensions for fabricating brackets on an axle, and get no response, and someone ACTUALLY knows what this is?

wow.

[Keith Armstrong]

Aha!

I told the tech I thought is was a wheel speed/abs sensor issue and he said NFW.

I'll have him re-seat the sensors and go from there.

Thanks,

KAA

[twirken]

Hey Keith-

My check engine light on my D-90 has been on for years now!! Mine has the same problem. My ECU got wet and was fried I think. So my light is perpetually on! So here is the skinny on the rough road sensor. The only thing it is for is to- irronically- not turn the check engine light on! With the new 4.0 motors in the 97's they have way more sensors and crap. So when the vehicle is off road the engine will have minor hicups and misfires and such which would in turn trigger the check engine light. So the sensors on all four wheels sense a difference in wheel speed and then tells the ecu-under the p-side seat- that the vehicle is off road and to ignore any minor hicups and misfires and to not turn the check engine light on. Then when you get back on road it then goes back into normal mode. So nothing will happen to the truck without this feature but you are correct the check engine light will stay on. So either take out the bulb and live with it or replace the ecu and or sensors. One thing to check and you can do it yourself is the go around to all four wheels and push the sensors down for the front and in for the rear. IF the sensors are not touching the cv in the front or the rotors in the rear it will not function correctly. I finally got tired of it and said forget it and am living with it.

Good luck
Tyler

[PTSchram]

You guys put the jinx on me...

Yesterday, a '99 DII shows up with the dashboard lit up like Piccadilly Circus on Christmas eve. Plug in the computer and the damned thing gives me an engine code of rough road detection-of course, I don't have the functionality to read the ABS codes. I also got the purge flow incorrect...

I think I'll work on Series trucks today.