Sootman

I started my truck this morning and the brake and ABS light stayed on. I started driving and noticed that my speedometer doesn't work until about 20 mph. When I go to stop it reads till about 25 mph then just drops to 0. I pulled the codes from the computer and got 2. First was 71- ECU RAM Read/Write Error.
Second was 72- ECU ROM Checksum Error. Does anyone know what these codes mean or what the problem might be! My guess would be the speed sensor but want to make sure.

armyret01

I had a Ford Ranger that had that happen and it was the ABS sensor that is mounted on the differential.

mishkaya

I'll second what armyret01 said, it is almost certainly ther rear wheel speed sensor located in the rear differential. It costs around $35 from what I recall. Relatively easy to replace as well.
Good luck
Mishkaya

Dlcorrie

My abs light and brake light came on around 30,000 miles. They told me it was the abs sensor, they fixed it and it came on again, they fixed it again and so on and so on...... It is still on, actually I think the abs light finally burned out but the brake light is still on. good luck

Mopardan

Yep, sensor on the diff. Been there, done that.

Sootman

I took the sensor out today and cleaned it off. Put it all back together and no lights and the speedometer is working fine. Thank you for all the replies!!!

nitrousn

make sure the terminals are clean where the wires plug on the sensor.

Ram44maR

Hey Sootman!

Let me know if you experience further problems with this.

Regardless, I posted a reply a while back to this ALMOST EXACT issue. You may want to perform a search on the following: "Rear Wheel Speed Sensor" If you do so, you should get one hit for a thread containing good info on this problem.

As you'll read, I experienced this issue with my '98.4 24v earlier this Summer...

Have a great one,
Bill [Ram44maR]

RATTLINRAM

My ABS and BRAKE idiot lights popped on during our trip to GA. BUT,,,,, everything else is working fine. The speedo, cruise, odo and brakes are normal. I'm going to replace the sensor on the diff, but I was wondering if there were any other things I should check also. Will scanning for codes give me any further info to narrow it down?

Ram44maR

Hey Dennis!

I appreciate the replies you've given me in the past [which I recall I've done for you also], so I'll give you my thoughts.

As I wrote to Sootman, I posted a reply to a thread a while back for almost exactly the same problem he is having. Unfortunately, OUR problems don't seem to match yours.

The problem(s) we've experienced are the classic "defective WSS" problem, where the speedo doesn't function until you approach about 20mph. As you would expect, this also interferes with proper auto tranny shifts [especially from 1st to 2nd].

As you're indeed getting the simultaneous ABS and BRAKE warning light syndrome that's usually symptomatic of a bad WSS, you may want to change yours.

Please PM me if you need part number info or pricing.

By the way, we may want to add each other to our buddy lists. I've spent the past SIX WEEKS repairing and/or preventing just about every possible fuel system issue I could think of. In all modesty, I believe I've been forced into becoming a 24v fuel system expert of sorts

Anyway, if you have a fuel-related issue with your '99, drop me a line...I've probably been there [please see that mine is a '98.5]

Have a great one,
Bill in NOLA

RATTLINRAM

Thanks Bill,
I'm going to pull the wheels and check all the brakes, plus check the WSS with an ohm meter. I still have the original brake shoes on the rear, so I need to check things over anyway. I guess this means I'll have plenty to keep me busy while I'm on vacation from work next week.

I will report on my findings when I'm done. I might even try to fix the sending unit for the fuel tank while I'm at it.

richard

I don't want to start any widespread panic here, but while you have your abs sensor out you might want to look down into the rear axle.
Check to see if your abs ring is still in it's proper location.
It is pressed on the backside of the carrier, so there should be no space between the carrier and the ring. the teeth should show no signs of wear.
If there is any sign of the ring scraping the cover, housing or warpage of the ring, pull the cover and check the bearings on the carrier.

Rich

RATTLINRAM

Thanks Rich,
I had read at least one post that mentioned the ring being messed up and it is about due for the rear fluid to be changed anyway. I'm kind of thinking that there may be a problem with one of the front WSSs since I'm not having any problems with the speedo or cruise at all. I'm also going to check the wiring up front because I had just replaced the crankshaft position sensor before I went to GA and maybe I pulled something loose when I was reaching down from the topside to get at the top starter bolt.
Thanks again for the replies fellas and I'll let ya know what I find.

Dennis

Ram44maR

Hello Dennis,

I read your response to my last reply [Sootman thread] and noted that you're considering a look at your fuel level sending unit.

As promised, I can probably help you with that one. Specifically, I have a variation on a couple of the old tried and true fuel level sender modifications you can find on the forums [including the dreaded PAY FOR TDR forum]

Anyway, let me know if you decide to tackle this issue. Not only did I modify the fuel level sender, but I did a long/drawn out fuel pickup mod as well. By the time the fuel module was modified and reinserted into the gas tank, the only thing totally factory was the actual module body itself [the upper steel half and the lower plastic half].

Now that I think more, however, the body isn't totally stock either. That's because the two halves end up getting permanently fastened together so their overall length matches the distance between the top of the fuel tank module threads [the threads molded into the top of the tank] and the bottom of the EMPTY tank.

In short, the fuel pickup is expanded to 1" ID and all the tank connections--fuel related and electrical--are modified to accomodate much quicker fuel tank removal/install in the future--WITHOUT picking up air leaks [NO quick connects].

Right now, my 24v is purring like a kitten: a kitten with 15.5 psi of diesel fuel being pumped through it . I've now got my FASS adjusted close to the target [13 psi] and my NEW VP44 seems to be liking life. In fact, it seems to be making very nice with my NEW RV275s.

All that's left now is completion of my a-pillar tri-gauge install [ISSPRO EV: EGT, mech fuel press and boost] and a bank of nice Contura rocker switches I'm installing in the cab [2 sets of aux lights and a master FASS switch]. The gauge job has turned out to be a much bigger job than anticipated, but I'm still buzzing about the great fuel pressure adjustment range I've seen: 8.5 to 29.5 psi with my FASS .

I hope your eyes aren't sore; I've just got a truckload of info spilling out of my fingers at the moment, which I attribute to the past six weeks I've spent with my CTD

Have a great one,
Bill

RATTLINRAM

I replaced the rear wheel speed sensor (RWSS) that is located on the top of the rear-end differential and my ABS and BRAKE light have gone off.

Now for a few findings that I came across before replacing it,,,,

*With the rear wheels up on jack-stands, The speedometer did not function at all when in gear at approx 30-35mph. (guesstamated),,,,, however, putting it back down on the ground and driving around,,,,, everything worked fine. (other than ABS and BRAKE light still on)
*When I removed the old RWSS, There was no continuity between the two prongs on the sensor.

I had a few options on what to do,,,
Spend the $60-some bucks for a dealer to put it on their diagnostic gismo (every shop I went to said that only a DC dealership could access the Controller for the Anti-lock brakes. (CAB) and I had already figured out that the CAB does not set any codes in the ECM that are readable by the average DRB scanner.) I figured I would gamble and spend the $33 for the RWSS and the reason for my decision was based on a theory that my front sensors were OK because the speedo and Cruise Control worked fine when all four wheels were on the ground.
This is only my theory and maybe one of our gurus can tell me if I'm correct or not.
On a 4 wheel ABS equipped truck, the CAB must get signals from all 4 of its data gathering sensors in order for it and the speedo and cruise control to function properly. [list=1][*]Front Left wheel[*]Front Right wheel[*]RWSS (remember that there is only the one sensor mounted on the pumpkin)[*]And the Transmission Speed Sensor which is mounted in the transmission.[/list=1]
When the RWSS fails on a 4 wheel ABS system, apparently the ABS shuts down and trips the warning lights to let you know it has disabled itself, however the CAB still sends the data from the Front sensors and the tranny sensor to the ECM, which enables the speedo and cruise control to be unaffected.
I also think, this is why the trucks that are equipped with only the Rear Wheel ABS systems have problems with their speedo's and cruise control when the Rear Wheel Speed Sensor goes bad. Evidently this system only uses the two data gathering sensors,,,
The RWSS
And the Transmission Speed Sensor

Does this sound like a fair explanation?

One thing I'm sure of,,,,,,,,,, I don't have those BLASTED idiot lights aggrivating me!

BTW the part number for the RWSS on my 2 wheel drive,,,, 4 wheel ABS equipped 2500 is 56028187AE and this is the same part number for the Rear Wheel ABS only trucks also.
NOTE* However,,, it does appear that the 4 wheel drive trucks have a different part number according to the parts guy I spoke with today.