1. Welcome to PlowSite. Notice a fresh look and new features? It’s now easier to share photos and videos, find popular topics fast, and enjoy expanded user profiles. If you have any questions, click HELP at the top or bottom of any page, or send an email to help@plowsite.com. We welcome your feedback.

    Dismiss Notice

(P)(!) BRAKE light and engine gauge

Discussion in 'Chevy Trucks' started by daniel_bergamini, Aug 26, 2003.

  1. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    Hahaha, so I have a 1991 Chevy Suburban with the 350 motor. Ok, so I played around with my truck a little and I have the following problems:

    1) Engine temperature gauge not working. It could just be stuck from lack of use - it's stuck below the lowest value 100. I bought a new sending unit because it was $7.99 and easy to replace but didn't bother cause I ohm metered the probe out and it's fine. I also put a volt meter on the connector and I'm getting a solid 5.00VDC on it. When I get the dash apart I'll finger the meter around and see if it was just stuck. Otherwise I'll buy a new gauge and replace the factory. What gauge (brand/manufacturer/model/size/etc) should I consider?

    2) (P)(!) BRAKE light is on. I don't believe it is the parking brake switch that is causing the light because the light actually gets a little brighter when I step on the parking brake petal. This implies to me that another circuit is closing and additionally illuminating the bulb making it brighter. This suggests that it is probably the differential sensor on the bottom of the brake master cylinder.

    How messy is this to swap out? Is there any way to test it? What is normal operating condition? Could it be an ABS fuse, boy wouldn't that be easy?

    3) I have an extra gauge pod in my dash, I was thinking of sticking a tranny temp gauge in there. Is there a more important gauge? How and where is the best/easiest place to put the sender for this?

    There will be more questions to come, this is just what I have right now. Thanks again.
    Last edited: Aug 26, 2003
  2. EZSnow

    EZSnow Senior Member
    Messages: 205

    what is your vehicle?
  3. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    What, can't you read? It's a 91 suburban. Just kidding, I just edited my original message to reflect the vehicle... Forgot I posted a new message instead of continuing my last thread which described the truck...

  4. wyldman

    wyldman Member
    Messages: 3,265

    If you have 5 volts on the gauge wire,the gauge may just be OK.You can gound the gauge to see if it goes full hot.If it does,it's either the sending unit,or the engine is running too cold (t-stat).

    If your going to go with an aftermarket gauge,I'd go with an Autometer.Good stuff,you can't go wrong there.I wouldn't try to put it in the cluster,as it's a real hack job,and not a lot of room.Mount any extra gauges under the dash,or use the little cubby hole above the radio( if you don't have air).

    It does sound like a problem with the differential switch for the brake light.Unplug it and see if the light goes out.The valve may not be centered,which will keep the light on.Some times rapping on it with a hammer,while pumping,or even bleeding the brakes will help.Some valves also have little rubber caps on each end,and you can manually center the valve.If that doesn't do it,then switch\valve replacement may be necessary.

    Tranny temp gauges are best installed in the trans cooler line to the rad.It is sometimes easier to just put them in the pan.The cooler line will read a more accurate,instantaneous temperature,where the fluid is hottest.The pan will read the fluid after is has been cooled,and will be more consistent.
  5. daniel_bergamini

    daniel_bergamini Member
    Messages: 41


    The truck is sitting out in a hot parking lot. Leaving everything hooked up the temp gauge seems to hover a little above 100 - maybe 120 or so. As soon as I turn the key to the on position it springs down to 100, key off around 120, key on... etc. I may be a little confused about the grounding of the gauge, should I just short the 2 pins together? I tried that and the gauge didn't pin to the top of over heat, but the check engine light did come on. Remove the paperclip that shorted the pins and everything was back to normal. The gauge also sat at 100 completely unplugged from the sender.

    I am pretty sure I'm working on the right sender here, I'm playing with the one right on the top of the engine next to the thermostat/radiator line. Is this in fact the sender that goes to that temperature gauge? I see something similar hanging off the exhaust header, but I assume that is an EGT or o2 sensor of some sort.

    On the brake issue whether I disconnect the harness from under the master cylinder or try and ground it out the light stays on. Not sure if it's related or just a symptom of an older truck but wiggling the ignition key makes the light change intensity.
  6. wyldman

    wyldman Member
    Messages: 3,265

    Your testing the wrong sensor.That's the ECT sensor for the injection system.No wonder the check engine light came on when you shorted it.

    The temp sender is in the drivers side head,between the first two cylinders.It should have a green wire going to it.Remove the wire,and the gauge should go all the way down,ground it,and it goes all the way up.The piece in the exhaust is the O2 sensor.

    If the brake lamp stays on when the switch is disconnected,then you may have an ABS problem.You will need to pull the codes to find out what it is.

    Connect a jumper wire between pins A and H in the ALDL connector under the dash with the key on.The brake lamp should start to flash codes.Count the flashes and report back the codes you got,i'll let you know where to go next.
  7. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    SUCCESS! sort of

    Well I work in IT, so you get what you pay for. This makes much more sense.

    So right you are. Part of the problem here is the guys at autozone gave me a ECT sensor - which is probably what I asked for... who knew the ECT sensor didn't control the temp gauge. The part I have has 2 leads and looks exactly like the ECT sensor right down to the color. Looks like I'll need the temp sensor now.

    Ok, if I ground the right sensor out, the light pegs overheat. I read the volts and I'm getting a solid 25.3 mVDC. Probing the temp sensor reads around 47 to 48 Ohms. Assuming I need to replace this sensor, will it be best to drain the coolant a little first or will it not spill?

    1 long 3 slow and this just repeats. Please tell me it's something quick and easy. Thanks so very much for the quick responses.
  8. wyldman

    wyldman Member
    Messages: 3,265

    One long,and three short flashes would be a code 4.Code 4 is a grounded anti-lock valve switch.

    Check the resistance between pin C and ground,and pins C and D,at the antilock brake valve.If either are greater than 50,000 ohms,replace the valve.If OK,turn ignition on,and measure voltage at pins C and D at the harness connector (to valve).If 4 volts or more,replace the valve.If not,the EBCM (anti-lock module) is bad.

    For the temp gauge,if it went full hot when gounded,and goes full cold when unplugged,then it's most likely the sending unit.Use a GM OEM part,no aftermarket stuff,as they are crap.It could also be a stuck thermostat,and the engine is running cold,but you would still see some small movements in the gauge.

    When you replace the sensor,let it cool off until there is no pressure in the hoses.Leave the rad cap on,it will help hold the coolant in.Put a bucket under the motor,and unscrew the sensor,having the new one in hand.Quickly swap sensors,with minimal coolant loss.Top it up,and your done.

    You don't really have to worry about airlocks,as those cooling systems use a radiator bypass,to bleed air out quickly.
  9. Mike 97 SS

    Mike 97 SS Banned
    from U.S.A.
    Messages: 1,106

    That happened to me once on my Chevy truck. That damn (P)(!) light would just appear after I started to drive and would just stay lit until I would shut the truck off and restart again. You know what it was? Bad brake light switch. Put a new brake light switch in and light never showed its face again. Mike
  10. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    Gentle - IT guy here. Where is the antilock brake valve? Is there any harm in clearing the code and hoping it doesn't return?

    Any guess what the one terminal part number is - one dealer argued with me that is it the 2-pin part that I have and it can be substituted and the other gave me 8993-146. Does that sound right?

    Thanks again.
  11. wyldman

    wyldman Member
    Messages: 3,265

    The anti-lock valve is directly below the master cylinder.It has a oblong four pin connector on it,as well as the brake lines going in and out of it.

    You could clear the codes,and see what happens.You need to pull the brake and\or stoplight\hazard fuse to clear the codes.

    The sensor should be a one wire,GM part number I got is 8993-146.It will have a button type terminal where the female spade kinda slides on at a 90 degree angle.

    There is also a part number 12503-332,which is a two terminal blade type,which they said can be converted to a one wire,but no details on how to do so.

    I would just get the proper button type,which is the 8993-146.It should work fine.
  12. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    1 pin 2 pin what's the difference

    I think it's the 2 lead type, and one lead is not used, just sits in a hole in the wiring harness. So the 2 lead is the one. Will replace soon and will diagnose the ABS soon too I hope.
  13. wyldman

    wyldman Member
    Messages: 3,265

    I'm not exactly sure what the difference is,but I'm assuming the 2 wire sensor has an additional remote ground.
  14. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    more nubie stuff...

    Should I put anything on the threads? any Torque recommendations? Thanks man.
  15. wyldman

    wyldman Member
    Messages: 3,265

    I usually use liquid teflon pipe sealant.The GM sensor's sometimes come with a red sealer already on them,but an extra dab of pipe sealant won't hurt.

    Don't have the torque specs handy,but usually just snug is enough.It's a tapered pipe thread,so it will get tighter as it goes in.It's brass,so you don't want it too tight.If your real anal on the torque spec,I'll dig it up for you.
  16. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    Ok hard evidence of something.

    Are we talking about the 4pin harness or the 6 pin harness handing off the bmc? Got a few values, but missed the C-ground one. Will go back out in a sec

    Swapped the sensors tighted it pretty good (no leaking) by hand and tightened it up as hard as the old one came out. Should be fine.

    What me worry? :cool:
  17. wyldman

    wyldman Member
    Messages: 3,265

    It the 4 pin harness you want.Pin C should be a dark blue wire,Pin D should be a black wire.
  18. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    1/2 way done.

    Ok both pin C & D and C & ground measure 5.38 Kohms. The harness is putting out 89mV with key on engine off.

    Temp guage works as expected, takes engine about 10 minutes to get to 120 then I shut her down. No leaks, little mess. Thanks so very much.

  19. wyldman

    wyldman Member
    Messages: 3,265

    You need to measure voltage at the EBCM side,not the harness side.You can either measure right at the EBCM,or diconnect the harness at the anti-lock valve,and measure there.

    LMAO I'm not that ugly. :D
  20. daniel_bergamini

    daniel_bergamini Member
    Messages: 41

    The EBCM being that black box mounted to the MBC? Will it have voltage with the harness disconnected?