Check engine light / Rough Road

[mhansen]

On my way down the hill today I hit a pot hole on I-70 ---really hard! My engine sputtered for a second, and the check engine light came on. Everything seamed to work fine, except for the light, but I did notice a little loss in power. Anyway when I got back near the house, about 45 minutes later, slowing and stopping at lights, the check engine light went off.

I thought that when the light came on with an OBD2 system it stayed on until reset.

Anyone have a clue to what set it off, and why it would have shut itself off?

Thanks for your help.

Mike

[Art Vigil]

Mine does that too - especially on washboard roads - it shuts off after a few days of driving as long as I don't repeat the incident. I believe it's caused by a malfunction of the "rough road" sensor.
I know that my vehicle has a recall related to the sensor that I haven't bothered to get fixed yet, you might check with one of the local dealers to see if yours does as well.
The purpose of the sensor is explained better by Alan Dobbs below (taken from the D90 source FAQ):


Subject: Re: [D90] Anybody know about the Rough Road sensor?

Alan Dobbs wrote:
> The function is just to let the ECU that you are in a off-road condition
> I.e. one wheel spinning. This prevents a check engine light from
> illuminating from a small misfire or a minor hick-up type condition
Close. It lets the ECU know that wheel speed varies so that it doesn't pickup that variation through the crank sensor and interpret it as a misfire and hence illuminate the MIL. Off road speed variations are sufficient to vary the crank rotational speed. Since the primary monitoring for a misfire is done at the flywheel with the crank sensor alternate causes of speed variation need to be monitored.

[mhansen]

THANKS Art!!

[mhansen]

Well after wrenching on my suspension last night I took the green monster out for a test drive. I was hammering the throttle down an on ramp to the interstate,and hit a bump, could feel the car loose traction for a millisecond and BINGO check engine light came on, this time it did not go off.

Called Land Rover they said they never heard of any recalls on the rough road detection system, and that there were no outstanding recals on my Defender.

Who sells the most economical (most bang for the buck) OBD2 scanner?

[dave_lucas]

Mike,

I can bring the OBDII scanner that I have to the meet and you can pull/clear the code if you would like.

[mhansen]

Thanks Dave!!!!!

[Art Vigil]

Dave you RULE! I just tripped my light again also.
See you Saturday, I guess I owe you a beer - you're a 'stout' guy, right?;)

[Monkeyboy]

So the dealer calls on Monday and says that they've got the correct software to solve my check engine light illumination caused by the rough road code.

They have the vehicle most of the day on Tuesday - glad I don't have to drive the '04 loaner Disco any longer - and I get it back last evening.

Leave the dealer, jump on the freeway entrance ramp with some enthusiuasm, over a little bump on the entry and yes, the light comes back on.

So, I know how to turn the light on. Just loose a little traction and get some uneven front to rear wheel speed.

Any brilliant ideas besides taking the bulb outta the holder :)

Thx,

KAA

[chrisvonc]

Theads merged

[mhansen]

Update on the rough road/ check engine light:

On a suggestion from Dave Lucas, I took the speed sensors out and cleaned them then reinstalled. I then cleared the check engine light with an OBD2 scanner and the light has never come back on. I have hit bumps hard and under acceleration (what mad it go on the first time) and it seams cured!

Thanks to Dave and all who helped!!!

[BarryO]

I'm getting code P1317, "ABS Rough Road Line Low Fault". Is this what you're talking about?

Excuse the newbie question, but where are the speed sensors?

[mhansen]

Barry-

Speed sensors are just behind the brake calipers on the rear axle. On the front they are on top of the swivel ball housing. They are the only thing on the the axle with wires attached. Clean around them good so dirt does not fall into the swivel ball housing or rear axle. I used WD40 and an old tooth brush to clean. Then wedge them out with a flat blade screw driver there is a lip on top of the sensor that you can pry against. Good luck

PM me if you need more help and I can get you my phone number and I could talk you through it

[BarryO]

Thanks, I see them. 'was wondering what those were, since the D-90 doesn't have ABS. So they're there just to sense rough roads?

I live on an unpaved road, and the sensors are completely covered with gunk. I'll make sure to give everything a good cleaning before messing with them. The rear rotors are due to be changed and I'll probably wait to do them both at the same time.

Not this weekend though; the front rotors on the wife's Disco need changing:

"honey, the brakes are making a funny noise"

Yea, metal-on-metal will do that ...

[mhansen]

Originally posted by BarryO
Thanks, I see them. 'was wondering what those were, since the D-90 doesn't have ABS. So they're there just to sense rough roads?

Well.....no.

They sense the wheel speed and send a signal to the rough road sensor that is under the passenger seat box. The rough road sensor in turn sends a signal to the engine Computer GEMS (in the white box under the bonnet) and tells it not to record an engine miss fire, because you were driving like a striped assed ape up your wash-board driveway.

The wheel speed sensor is a small magnet and coil that basically produces electricity when a piece of metal is passed by it (think little tiny alternator). The swivel balls in the front of the '97 have groves in them. These groves pass just in front of the sensor. The faster they go by, the more electricity is generated, and the higher the frequency. The rough road sensor measures the frequency and determines if you are driving fast or slow.

To determine if one is bad you must disconnect and measure the resistance of each one, with a multi meter (ohm meter) they should be relatively close the each other, then switch the meter to AC voltage and and spin the wheel and measure the voltage of the spinning wheel. The voltages should be very close.

Now someone out there will say that voltage is amplitude not frequency, but they should be linear and the only way to check.

To test I used two digital multimeter's of the same make and hooked them to each side of the front. Jacked up the front and spun the wheels. With open diffs, one wheel spins forward and one in reverse. The sensors don't care which way the wheel is spinning. they just care how fast. I made sure they measured the same, and then repeated in the back.

This procedure takes a while to do, and was unnecessary as I found that the sensors were good, I would recommend cleaning the sensors and reinstalling first, then go to diagnosing a bad sensor.

BTW--Drink allot of Fat Tires (or the Ale of your choice) and it will be easier to understand.

[Screehopper]

Anyone with an obd-2 scanner in the Los Angeles area (More specifically in the Alhambra/MPK area) that can help me read the codes off of my disco? I'd greatly appreciate it.

This Memorial Day weekend I did a bit of offroading in my '97 DI and now the check engine light is on. The light did not come on until I got home. I was idling on my driveway as I unloaded a few things into the garage. When I returned to my disco to move it off the driveway I noticed that the check engine light appeared. I'm hoping it's just due to the washboards that I went over.

[m.michaels]

I have read the "Rough Road" fault threads - but believe I have a new wrinkle.

1) Check Engine Light Comes on
2) Drive with it on for a couple of weeks and it goes off
3) Right before my State Inspection - Check Engine Light Comes BACK on
4) Take it to my local Rover guy
5) Their high dollar Land Rover diagnostic tool can't talk to the ECU
6) Take my ECU and put it in another 97 D90 - viola they can now "talk" to the computer
7) Start looking at the wiring harnesses for the ECU and tracing wires
8) ECU is fine, but if they unplug the ABS computer they can now talk to the ECU AND get my car inspected
9) They call the dealership to talk with one of the guys they like - and he said that occassionally they have problems with the whole ABS unit - and they solve it by upgrading a PROM in the ECU that ignores rough road codes but lets legit fault codes through, and that whenever they want to diagnose this guys D90 they unplug the ABS to talk to the computer.
10) My SPEEDO doesn't consistently display the mileage on the Odometer (it mostly flickers heiroglyhpics). Is the speedo LED bad, OR is this some feedback loop where the speedo is screwin' with the ABS . . . .

I asked why can't I just leave the whole ABS piece of CR*P disconnected, to which I get the response that it controls the speedo and some engine management functions - like how much fuel you need at certain speeds etc. He said that Land Rover did not provide any schematics for the ABS computer so diagnozing the thing would be a losing proposition - at $70/hr I had to agree . . .

Has anyone experienced a similar problem? If so what did you do to fix it? Does anyone have an idea of how to diagnose the ABS system for the :angry ABS I don't even have?

When I build my own D90 you can be sure that it will run with a wire from the battery to the starter!! No ECU/ABS bullsh*t. I love my D90, but it ain't feelin' too bullet proof right now!

[chrisvonc]

matthew.. I am merging this with the existing thread in case there are other suggestions.