ABS Wheel Sensor Replacement 1996 Chevy 3/4 Ton 4X4

[tinkering]

Originally Posted by j cAT

resistance is not really a good test. the sensor output voltage test is needed.

sensor may read good resistance and I think the 1100 ohms is a good reading as the 1994 sensors read that amount but what is required is the proper voltage output which checks the sensor and what they call the sensor gear ring.

Hi j cAT,
Both the installed sensors have the same 1100 ohms as well.
I will do the cranking output voltage test as soon as I can get my hands on a multimeter that does AC volts.

[tinkering]

Originally Posted by j cAT

I would guess that the rear sensor is working . the front sensors I would use a volt meter ac volts crank hub by hand at a good rate and you need more than .25 VOLTS AC . a good new sensor will put out .5 volts ac or more.

place a deep socket on the lug stud and use that to crank the hub around .

sounds like they used a different hub assy . look up the correct hub assy part and see whats different. which one is wrong . the front sensor outputs should be close or you will get these issues.

until you fix this remove the big ABS fuse. this will prevent any ABS activation to avoid brake failure.

I will do the cranking AC voltage output as soon as possible. I am interested to see if the 2 outputs are close to each other.

My parts guy said there is only one hub assembly listed for that vehicle from 1996 to 2000. That may be true but maybe the previous owner installed a hub assembly from 1995 or from a 1 ton or something? I am going to order the drivers side hub assembly and see if it matches the one that is raising our eyebrows. If there is a slight difference in the the air gap because of a slightly different reluctor ring gear, or slightly different reach of the center electrode of the required sensor application, it could cause an imbalanced signal to the control unit; bringing the light on? Sound plausible to you?
It's too late to order the hub assembly; the parts store is closed for New Years Eve. I will see if there is anyone around there tomorrow; maybe I can have it by Thursday AM.

Happy New Year Merry Christmas still.
tinkering
I will take the big ABS fuse out for now. Thanks

[tinkering]

Originally Posted by j cAT

... 1994-96 are not good years with this GM ABS system. many known ABS valve body failures...

If this suspicious hub assembly isn't the culprit (I am very suspicious of it) then I will have stay encouraged, and be prepared to check out and change out whatever is necessary including connectors, grounds, conductors, the valve body pump control unit (definitely wrecker$ material). Maybe the ring gears just need a good cleaning. Here's hoping

[tinkering]

Originally Posted by rhandwor

...Use your DVOM set on ohm setting. Rotate each wheel by hand. The meter should go from zero to one as the tire is rotated.
One end of the meter on each terminal. If it doesn't change its bad.

Is it OK to run a current through the ohmmeter; we were always told not to?

[rhandwor]

Originally Posted by tinkering

Is it OK to run a current through the ohmmeter; we were always told not to?

Mine has a fuse that will blow if hooked up wrong. Mine has a dial on the front which when turned to go from volts to amps.
My test was just a basic test to check if its working. The manuals use different tests
sensors pulse as the wheel turns. Like the old points open and close as the cam rotated. These sensors must have a spring and magnet that opens and closes as the wheel turns. I have a good logic probe that you can watch the current pulse as the signal changes. The computer sends a low voltage and the sensors pulse the voltage.

[j cAT]

Originally Posted by tinkering

Is it OK to run a current through the ohmmeter; we were always told not to?

the ohm meter is for NO voltage use. only on measuring for resistance with no power applied.

Now on the speed sensors. these operate by a rotating ring with teeth on it . the sensor is a magnet with a coil. when the steel teeth pass the sensor pick up end the magnetic field is disturbed and a voltage is generated.

there is no switching and it is not like a points distributor set up.

the crank sensor works the same principle. as the engine rotates a voltage is created . the PCM count the pulses to determine the RPM . abs sensor the PCM counts the pulses to determine the vehicle speed.

working on much larger transportation vehicles with these sensors exposed to debris they being magnetic pick up iron dust and then the sensor output falls. also the gap can get out of calibration.

[rhandwor]

Ideas for you to look for.
http://www.popularmechanics.com/cars...enance/2265091

[tinkering]

Originally Posted by rhandwor

Ideas for you to look for.
http://www.popularmechanics.com/cars...enance/2265091

Thanks for that

[tinkering]

Originally Posted by tinkering

If this suspicious hub assembly isn't the culprit (I am very suspicious of it) then I will have stay encouraged, and be prepared to check out and change out whatever is necessary including connectors, grounds, conductors, the valve body pump control unit (definitely wrecker$ material). Maybe the ring gears just need a good cleaning. Here's hoping

Bleeding the pump body sounds like a nightmare. Has anybody done one of those!? I really don't relish the thoughts of 'THE BLEED'; the popular mechanics link http://www.popularmechanics.com/cars...enance/2265091 mentions the need of a certain scanner that is needed to bleed the valve body! Here is a great demonstration http://www.youtube.com/watch?v=jdiOlEKTqrE
This YouTube shows how to pull the electronic box off of the top of the valve body, and change it out safely http://www.youtube.com/watch?v=lUotkKXG9dY
This YouTube shows how to repair the electronic box http://www.youtube.com/watch?v=Jo76ylqgUR8

This YouTube search has most of the info needed I think (except for the invaluable knowledge base of Automotive Forums) bleeding abs pump chevy - YouTube

I like this neat demonstration of how to free a seized bleeder with a torch and a rag (should you use heat on the brakes? http://www.youtube.com/watch?v=KnJ4IQVritU

Is anyone ever going to give me my first 'Thanks' ? I guess I need to join in on other folk's threads to get those)

[j cAT]

The video of the bleeder removal with a cutting torch is not how to remove a difficult bleeder fitting. also you do not use a box wrench.

If I find that the bleeder is stuck I use a socket with 6 points then try to remove. this lessens the possible breaking of the fitting.if it still does not loosen I get a small tipped propane torch and just heat up the fitting. then when the fitting is looking a little red place the cold socket on the fitting and gradually rotate/increase force to loosen. as the fitting shrinks it will break loose. doing it this way the fluid should not get damaged. also replace these fittings. since the fluid is now heated before pushing the piston back open the bleed screw and push back the piston. you will see debris in the fluid. if the pistons are pushed back with not dumping this piston fluid this is why many ABS valve units fail. this is my procedure when doing the brake jobs . the piston fluid is always dirty and damaged.

[tinkering]

Originally Posted by j cAT

The video of the bleeder removal with a cutting torch is not how to remove a difficult bleeder fitting. also you do not use a box wrench.

If I find that the bleeder is stuck I use a socket with 6 points then try to remove. this lessens the possible breaking of the fitting.if it still does not loosen I get a small tipped propane torch and just heat up the fitting. then when the fitting is looking a little red place the cold socket on the fitting and gradually rotate/increase force to loosen. as the fitting shrinks it will break loose. doing it this way the fluid should not get damaged. also replace these fittings. since the fluid is now heated before pushing the piston back open the bleed screw and push back the piston. you will see debris in the fluid. if the pistons are pushed back with not dumping this piston fluid this is why many ABS valve units fail. this is my procedure when doing the brake jobs . the piston fluid is always dirty and damaged.

6 point always. I thought the video shows pretty extreme heating of the fitting and area (and the fluid); I like your prescribed touch. Whats wrong with cooling it with a rag? That is real good thinking j cAT; dump the affected fluid out via the bleeder before squeezing the piston back. How would the damaged/dirty fluid find it's way from the caliper piston back into the ABS valve; would there be enough fluid pushed back from the piston to reach the master cylinder (and work it's way from there to the ABS valve)? Regardless, it is very wise thinking to expel that damaged fluid, and debris from the system.

This is a perfect example of why I say Automotive Forums' knowledge base it invaluable. THANKS

[rhandwor]

Push the brake pedal slowly and refill the master cylinder after each bleed. I replaced the valve body unit on my sons 1997 two wheel drive. I had to use a scan tool to bleed it properly.
When I lived in Ohio I had to use a torch to free up bleed screws.
His truck had bad wiring as I went to a scrap yard and got used harness and a spindle.
I got rebuilt calipers and a used rotor. The wiring to the speed sensor on the transmission was also bad. The valve body was also from a scrap yard. I had an OTC 4000E and I had to get another module and connector. It was last updated to a 2002 duece and a 1998 module for brakes. At this point they required you to buy a new scanner around $2000 as I was retired I didn't buy a new scanner until I got some cheaper scanners.

[j cAT]

Originally Posted by tinkering

6 point always. I thought the video shows pretty extreme heating of the fitting and area (and the fluid); I like your prescribed touch. Whats wrong with cooling it with a rag? That is real good thinking j cAT; dump the affected fluid out via the bleeder before squeezing the piston back. How would the damaged/dirty fluid find it's way from the caliper piston back into the ABS valve; would there be enough fluid pushed back from the piston to reach the master cylinder (and work it's way from there to the ABS valve)? Regardless, it is very wise thinking to expel that damaged fluid, and debris from the system.

This is a perfect example of why I say Automotive Forums' knowledge base it invaluable. THANKS

when you drain the cal pistons with my method into a container using a clear plastic tubing routing higher than screw port then lower into your container. as you push back slowly using a C clamp the debris amount will surprise you. those particles will screw up the ABS valves from seating properly. I have found even in new calipers a lot of dirt / material. then with the piston fully back close the bleed screw . load calipers then do your normal bleed procedure to remove any air ..usually none.

only work one brake unit at a time.

[Schurkey]

IF (big IF) the vehicle has stock-type rubber brake hoses, it's useful to lightly pinch the hose to absolutely prevent contaminated fluid from being forced backward through the system.

In the early years, I used a needle-nose vice-grip to lightly pinch the hose. Now I use dedicated hose-pinching tools. Either way, the hose doesn't have to be clamped tightly. Just enough to prevent fluid flow.

DO NOT do this on aftermarket steel braid/Teflon liner brake hoses. They are RUINED when pinched.

[tinkering]

Originally Posted by tinkering

I will do the cranking AC voltage output as soon as possible. I am interested to see if the 2 outputs are close to each other.
My parts guy said there is only one hub assembly listed for that vehicle from 1996 to 2000. That may be true but maybe the previous owner installed a hub assembly from 1995 or from a 1 ton or something? I am going to order the drivers side hub assembly and see if it matches the one that is raising our eyebrows. If there is a slight difference in the the air gap because of a slightly different reluctor ring gear, or slightly different reach of the center electrode of the required sensor application, it could cause an imbalanced signal to the control unit; bringing the light on? Sound plausible to you?

I did the cranking AC voltage output test. The passenger side sensor put out 0.4 VAC while cranking the hub with a socket on a lug stud; as fast as I could. Guess what? The drivers side produced zero VAC! That is very encouraging to me.Now I have thicker suspicions that the wrong hub is on the drivers side. Both of the wheel sensors measured 1100 ohms so I was expecting to see some kind of out put there. I am going to order the correct hub and do a visual comparison; I will also check the ring gear for fouling, wear and/or breakage on the next above freezing day we get here.