schoust

Hello Guy's had a strange thing happen this am on my daily driven 95 12 valve. I started the truck and like alway's the brake light and Abs came on and this time did not go out until I shut the truck off after I arrived at work 17 miles later?? I have since driven it again and the lights are operating as normal again. Is there some sort of relay hanging up? Maybe a short? What cycles these lights? By the way I don't have abs?

snball

First thing I'd check would be vacuum line. I know there is a small line that runs up and ties into the vacuum line at the top of the fire wall just inboard of the master cylinder/booster. In variably whenever I work in the area of the injection pump or fuel filter, when I get in and start the truck the ABS and brake light stay illuminated because I've bumped the vacuum line and knocked it loose again.

schoust

Hmm wouldn't that cause the lack of brakes? The brakes work fine I was thinking the same thing to but then tested the heck out of the breaks and they work good. Whats strange about this is it has not happened since? It's almost as if there is some sort of a start sequence coming from the PTM that does this and somehow it hung up?? Concerned because I drive many miles a week and rely on this truck for work... By the way snball Welcome aboard!
& Thanks

snball

I'll have to dig into the service manual diagrams to see exactly what the small (1/8" inch) vacuum line does. But it has happened to me several times - brakes work fine (not a big enough leak to affect the booster) but the ABS and brake warning lights are on. First time I was afraid I had a major problem, now I know pop the hood and plug the line back in.
And thanks for the welcome.

snball

Since there is no manifold vacuum on the diesel there is a vacuum sensor that detects a low vacuum condition and sets the brake light. If the vacuum line to the sensor leaks it won't drop the system vacuum enough to affect the brake operation but the sensor sets the light.

justme-

I have had the exact same thing happening for over a year with no resolution yet- had to pull the lights from the dash for an inspection. Bought a new diff sensor, yet to install tho. Changed all the brake lines and the ABS valve too, have not put the lights back in yet. No codes register from this.

Lots of reading pointed to the vacuum (Which I now have a vac leak- 2 pedal presses and I loose boost) or the rear sensor. When checking the lines I saw the ABS valve solenoids were pretty rusty so I went on a 9 month journey searching everywhere for a new valve- dealer wanted almost a grand- one place listed them but when I went to order they were not avail any longer. Finally got lucky and found one in a junk yard in AZ!

schoust

So I guess the next question is what are most probable places that our trucks can loose vacuum? My breaks have really never seemed that great and to be honest I thought that was typical of these years? I'm starting to think that is my problem..

Astro

Stolen from another thread...

This is for 96 and older.

"Oh no, my ABS and Brake Light are on!"

--------------------------------------------------------------------------------

If your ABS light and brake light come on, in most cases it's probably your Rear Wheel Speed Sensor (RWSS). This sensor is on top of the rear differential.

This sensor is controlled by a "exciter ring" that is interupted by the teeth on the ring sending a variable voltage signal to the computer depending on vehicle speed. small metal shavings can cause it to fail over time. The most common symptoms of the switch's failure are bad speedometer readings and tripping the RWAL computer located under the center of the dash.

Other obvious things can also trip the computer such as:

1. bad pads, shoes, calipers, wheel cylinders.

2. bad fuses.

3. poor connections or broken and/or chaffed wire.


Once you have detemined that none of the above exist, you can try a system reset buy pulling the abs fuse and/or pulling negative battery terminals for 30 sec or so.


If the lights come back, the next thing to try is reading the RWAL fault codes.

To read the codes on 96 and older trucks:

1. turn key to the "on" position.

2. for just a second, ground pin # 13 on the diagnostic plug located on the knee bolster (#13 is a black wire, it's the 4th from right bottom row).

watch your ABS/Brake light for codes.

start counting with the first long flash, end with last short flash.

there are only 13 codes.


1. Not used.
2. open isolation valve wiring or bad control module.
3. open dump valve wiring or bad contol module.
4. closed rwal switch.
5. not used 4wd. over 16 dump pulses in 2wd.
6. erratic speed sensor reading. (most common)
7. electronic control module fuse pellet open, isolation output missing, or valve wiring shorted to ground.
8. dump output missing or valve wiring shorted to ground.
9. speed sensor wire resistance/ high reading.
10. speed sensor wire resistance/ low reading.
11. brake switch always on, RWAL light comes on over 40mph.
12. not used.
13. electronic control module phase lock loop failure.
14. electronic control module program check failure.
15. electronic control module RAM falure.

mine was a code 10. it was a break in the molded section of wire off the RWSS.

*On 97-98.5 12V models, you will end up at the dealer to get the ABS codes.

schoust

I could believe this if my Truck had Abs. I does not.....I am leaning more toward the vacuum deal because that line that we talked about that runs along the fire wall appears to have a small crack in it right next to what appears to be some sort of coupling thingy? If this is indeed damaged how does one go about replacing this sort of line? It looks to be some kind of plastic??Any vac line I have ever seen has been rubber. I think I would like to replace it to be sure,Any ideas??

infidel

I thought all the '95s came with at least rear ABS, four wheel was an option.

justme-

I thought every vehicle made had to come with ABS these days- coworker bought a new car 2 years ago without abs. I have been asked if mine has abs or no when checking for parts for what that's worth.

The vac line you're talking about can be spliced with regular rubber line to repair the crack. If need be a regular vacuum "T" can be used if the crack is too close to a molded "T".

I read that other thread related to the diff sensor, have not replaced mine yet, but if the other truck has no abs...
It could also be the vacuum pump- they do wear internally and the seals go. Seal kit from Cummins is cheap.