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Blinking brake light and spongy pedal

Discussion in 'The Garage' started by Broncoholics.com, May 11, 2005.

    90' V2500 burb. TBI350/400.

    Not sure they are related. Just realized after owning this burb for a couple months that the flashing brake light is giving me a code: 9 quick and 1 solid. After searching, I am coming up with this:

    Code 9: open or grounded speed signal circuit

    Got that code off this thread:
    http://coloradok5.com/forums/showthread.php?t=74676&highlight=Brake+light+codes

    Anyone know how to fix this, or where to even start?

    Also, within the last couple weeks I have noticed a pretty spongey feel in the braking system. The pedal will fade at stop lights from time to time, but its becoming more frequent, so I am guessing that either 1) they are related or 2) that the master cylinder needs replacing.

    Just curious if anyone has had a similar issue. I never had an issue with the braking up until last week, which is why I don't think they are related, but would still like to fix both. Any ideas?
     
    Last edited by a moderator: May 11, 2005
  1. Okay, this is very good reading for anyone having brake issues:
    http://www.babcox.com/editorial/tr/tr89850.htm

    So, after reading that I realized I had a false code, so after pulling the Stop/haz fuse for a few seconds, my blinking brake light is now out. No change in the pedal feel though, so it looks as if I will be replacing the MC tomorrow.

    Any tips on bench bleeding the new unit?
     
  2. mechted

    mechted 1 ton status Premium Member

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    just follow the instructions on how to bench bleed and it make sure you dont max it out, you could hurt the seals before you even get it on the truck
    should be a relatively pain free process... until you have to bleed the brakes by yourself.... that can be tricky
     
  3. Pookster

    Pookster 1/2 ton status

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    that sounds like a MC issue, more than an electronic issue. I've had that before; it was the MC- if you are at a stop light, try clicking the AC on and off. If the pedal feel changes, its the vac booster and the MC thats the issue.

    At least that is my guesstimate.
     
  4. Okay, new MC is bled and installed and the brakes feel good. I reset the brake light and now the light comes on at 35mph and stays on. No blinking, just a solid light.

    So, I assume that it has to be an ABS issue. Anyone else have this issue?
     
  5. suthrnchvyguy89

    suthrnchvyguy89 Registered Member

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    my brake lights been on for the past couple days and i still dont know why, im taking it into the shop tomorrow though...
     
  6. Pookster

    Pookster 1/2 ton status

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    Let me know when you figure it out... I've been working on that problem on my truck after a rear hard line developed a leak and I replaced it. All I know is that the rear is inadequately proportioned to the front.. the rear will lock up real fast.

    Do you have the same problem?


     
  7. No, with the 35s, I haven't locked anything up. I think it may have to do with needing to reprogram the DRAC. But, you need a kit from a GM dealer to do it.

    This is from the link I posted earlier:

    "If non-stock tires are installed on a GM vehicle with a DRAC module, therefore, the DRAC module must either be replaced or recalibrated. On 1991 and earlier "C" and "K" pickups, the DRAC modules can be recalibrated for different tire sizes and axle ratios by changing the configuration of an 8 pin connector that plugs into the instrument panel circuit board connector. A DRAC recalibration kit from GM is necessary for this procedure. By referring to a speedometer calibration chart in the factory service manual, the correct pin positions can be determined for any tire size and gear ratio combination. The specified pins are then broken off the connector. This alters the DRAC circuits when it is replaced in the instrument cluster to recalibrate the vehicle speed signal.

    The "S" and "T" Blazers and vans as well as '92 "C" and "K" pickup truck applications have a DRAC that is a sealed plug-in module referred to as a "Vehicle Speed Sensor Buffer." It is matched to the original gear ratio and tire size of the vehicle, and cannot be recalibrated. Any changes in tire size or axle gearing requires replacing the DRAC or buffer with one that's correctly calibrated for the tire size application."

    My burb appears to have the same system as the trucks listed. I know that it has rear ABS or RWAL(rear wheel anti-lock) based on the ABS module next to the master cylinder. For now, I am going to leave it alone since the braking seems fine, and I don't think that the ABS is going to work correctly with the 35s anyway. But, I am going to take it to the dealer to have the codes run.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Do a search for DRAC on this board. I did a post on it that has links to do all the recalibration yourself. It's not hard, I find it funny that it's mentioned you need a kit. :)
     
  9. Cool, thanks man! Just what I needed. And to make it easier for some people, here is your post:

     
  10. Hey Dorian,

    Do you happen to know if a 1990 V2500 Suburban(4wd) has the 40 pulse VSS? Also, I'm having a hard time seeing the damn thing under the dash. Is it locted there or behind the glove box? (fat ass can't manuever enough to see it) :D :mad: ;)
     
  11. Okay, I reprogrammed the DRAC. Speedo is improved, but the damn light still comes on at 35mph. :mad: Its not giving me any kid of code, just a solid light. Any other ideas?
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Sorry, didn't have internet this weekend.

    I know only a little about the RWAL system, but from my knowledge of the non-RWAL setup injection systems, that brake light should have nothing to do with the injection, hence the brake light which should make correction/diagnosis fairly easy. The 35MPH issue is interesting, that MUST be some kind of threshold to trigger something, (or something screwing up the system that may not be able to trigger a "real" code) but I'm not sure what would be so critical to RWAL over 35MPH.

    I'm assuming if you pull the RWAL fuse the light doesn't trigger?

    IIRC the RWAL system utilizes it's own control module, so there should certainly be some specific data for it in the service manual, unfortunately I don't have any of the manuals that are that new.
     

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