Hi,

My ABS light is on. I cleaned and tested my rear diff sensor and I get 1.3K Ohms. Is this a normal reading for this sensor?
Thanks

 

What year truck?

 

Hi gorms,

Oh ya it is a 97, 5 sp. rear ABS only.

On the same ABS issue do you know a sure fire way to tell if the prior owners may have disabled the ABS altogether? I read there is a pump of some sort below the master Cyl. I cannot see anything but waht may be the proportioning valve having a 4 wire plugin and a 1 wire on the side of it???

When I start the truck it initially goes out ( the light ) then comes on after about 30 seconds.

I just replaced the rear wheel cyl(s). today and bleed the rears too.
Still light on I believe the fuse on the side is ok and the 40 amp relay under the hood too.

 

The ohm reading sounds OK.. When mine went it was totally open. I would really check the harness to and from the sensor, mine was mulched from the gravel hitting it and I had to splice and heat shrink some sections.

 

I've never messed with the sensor but isn't it just a magnetic switch triggered open and closed by a magnet on the differential gear?
Computer counts the pulses.
Seems like it should just be open or closed.

My method of testing has just been to keep a known good spare around to swap in.

 

Hi Infidel,

Your analogy seems to make sense. I checked with the local BC dealer and was told the sensor is $87.00 plus our lovely HST of 12% Tax here in "Beautiful BC" so kinda pricey, would be nice to know for sure but I can only imagine if I take it to the dealer it would be prob. $400.00 to re:re the sensor with labour/diagnostics/part/tax.

Will have to look at the wiring again may be missed something.

I just bought the truck and am fairly alright with doing things on a vehicle but this is my first Dodge so I am not familiar with anything on it.Will take some time but I like the heavy duty capability over my prior toy 4x4's

 

You have to get the sensor from Dodge too.. I tried aftermarket but every place I went to said they were back ordered indefinitely from their sources. It didn't matter if it was Can Tire, Napa, Bumper to bumper, AutoValue, Autopro . they all said the same place made them and they were not coming any time soon. It was cheaper at Dodge anyway.

Bill. The sensor is an inductive pickup, magnetic core with a coil around it. This senses the tooth count on the sensor ring on the ring gear to sense rear axle speed. If the sensor gets filings on it, the will start to lose count and trip the ABS lite. It needs notch or movement of a ferrous surface to create a voltage.

If the circuit is open you would get the light right after start. Thats where I would suspect the harness or sensor.

 

The ABS speed sensor in the rear diff should read about 1.3K ohms. The resistance will increase a little when hot and decrease when cold. The sensor is made by winding copper wire around a magnet. When the teeth on the tone wheel pass by the sensor, the magnetic flux will change and generate a voltage spike. The ABS computer reads this voltage spike to determine the rear axle speed.
I don't think the sensor is your problem. One common problem is the wiring connected to the sensor. Many trucks have the harness abraded where it goes over the frame just behind the fuel tank. Check for damage and good luck.
I see Lil Dog beat me to it.

 

Hi Bent Valves,

That is bad valves must be straight.

I checked the wiring and it was ripped apart at 1 pt. but it did not fix the light.

I was reading that this truck has 2 sellaniods "can't spell" that are part of the ABS system well I looked below the mcyl and I think I see what may be them and the power wire was also Not connected so I connected it to + battery and started and still light come on after 30 secs or so. So prior owner "who did squat" for fixing anything on the truck had purposly disconnected it but I would like it to work so I will have to trace the line back to the sensor fully.

Thanks for your input/info.

 

Could be the previous owner didn't like ABS and disconnected it on purpose.
Wires in that area also have a habit of accidentally being disconnected during a fuel filter change.

 

Hi infidel, Yes possibly true assumption but I need to pass a inspection so "everything" must work. The prior owner neglected to tell me about this and when I called him he played dumb about not knowing.. then O-ya I did get a ticket for having the windows tinted that he did not pay and now Big Brother ICBC has flagged the vehicle for an inspection. very difficult to comply with and must be Towed to an inspection place to be assessed. PITA.

Not the best way to jump into my first Cummins truck but hopefully I can get it through but will no doubt be costly.

 

My bet is all they will check is to see if the warning light is on.
Just remove the bulb if it comes down to it.

 

Yup.. Fix it later.. The rear ABS is a joke anyway IMHO.. I think I have felt it work maybe once... Once the diff stops turning, it stops working. Usually both wheels stop at the same time for me so it doesn't know the difference between a full stop and a slip.

 

Thanks for the help ppl.
I will have to remove the bulb to pass the bs inspection. I have heard it is a potentially dangerous here in the forum. Probably better without it.
oao

 

Does the brake pedal drop slowly when you stand on it? If so it is the ABS unit under the master cylinder. You can get one off a 1500 gasser at the U pull.