Cruise Control Diagnosis 98 Suburban

Discussion in 'General Chevy & GM Tech Questions' started by nhebayer, Mar 25, 2014.

  1. nhebayer

    nhebayer New Member

    my first official post. Please forgive me if I am repeating another question. I searched and did not really find any specific answers. I am hoping someone can help my before I dismantle this truck. LOL

    Back ground... truck is a 98 Suburban 4wd with 5.7 engine 168,000 miles.. appears to be in excellent shape. No check engine or ABS lights on. it runs and drives perfect.
    I purchased this like I do most of my trucks. It did not run and I have no history on it. Replaced fuel pump and fuel regulator and it runs awesome. We want to use it for traveling and camping.

    The Cruise Control... When I try to set it... once in awhile it will engage for a few minutes and shut off. most times it wont work at all. Past experience says its the Switch... So I bought a new switch and replaced it with no change. in the interest of saving rime I pulled the Cruse module off my other truck to install for testing... a known good part... Same thing.
    I did a google search and found this ... its an awesome site with alot of great info.
    I did the circuit tests from the site and it all checks out except terminal D... it comes from the Brake pedal... suppose to have 12V and drop to zero when braking... Well its got 4.75 Volts and drops to 0 when braking. Obviously this is a problem.

    This circuit is also tied into a Body Control module I think... I have Diagrams from a 01... Same Cruise Mod and Multi switch.. so I am pretty sure its the same design.

    The Brake switch is buried up under the dash so deep I will need to pull the steering column to get at it.

    My Question is... Has someone ran into this problem... and am i looking at a switch on the brake pedal or a Body control module?

    Sorry for the long post. Thank you
    Reaney in NH
  2. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    Hello nhebayer.

    I would start with checking the wire between the BCM and the module. Make sure the contacts are not corroded and that the wire is not chafed and touching something that might be providing a partial path to ground. Work backwards from the problem you have found. the switch might be dirty and intermittently be sending an open circuit signal to the BCM. Make sure the switch is good and that all the contacts are clean.
  3. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    The switch is a know problem area, but I thought it was mounted on the brake pedal, or next to the brake pedal.
  4. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    I would also lean toward the brake switch. I have never had to pull a steering column to replace one. Just by a new brake switch retainer, so you can break the old one when you take it off.
  5. nhebayer

    nhebayer New Member

    Its Fixed... I thought I would update what I did to finish Diagnoising and the fix for others to learn from.

    As stated above I have 4.75V at the Purple wire on the plug at the cruise module. This wire comes from the Brake switch on the pedal.. it is supose to have 12V with key on... and drop to zero when you step on the brakes.
    The concern I had was that the BCM also draws off of this wire.. and I wondered if the cause was the BCM or bad switch. Easy enough to check... just check the voltage comming directly out of the switch... OH OH... We have a problem. I can barely see the switch and i
    I cant get my hand within 6 inches of it. WOW... That thing is buried on this truck.
    So... Remove lower dash panels... remove dash brace section... remove single bolt on steering shaft... unplug harness to column ...Remove 4 15mm nuts to drop column..I left shift cable hooked to column.. Droped column to the floor. Lots of work to acces a simple switch.
    I pulled the switch leaving it plugged in and restested voltage on the purple with and had the same 4.74 volts. Unplugged the switch to remove to work on it on the bench.
    I checked Ohms resistance on each of the 3 circuits for comparison... 2 are normaly closed... and one open. my circuit with the purple wire and high resistant reading os about 33ohms... others test with 1ohm or less when closed.
    I took the switch apart and inside were brass springs with small contact points. I used a small file and cleaned all the contacts and retested and then it tested good.
    I put the truck all back together... installing the steering column with the steering whell exactly 180 degrees off. LOL Just my luck.
    Test drove and it worked perfectly.

    I hope this is helpfull ro others that run into a Non working or intermittent cruise control. the link to Sparky's page was awesome... it told me what to check and what the readings should be. After that it was Follow the leads.
    Thank you for the input.

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