# (P)(!) BRAKE light and engine gauge



## daniel_bergamini (Aug 25, 2003)

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.


----------



## EZSnow (Aug 13, 2003)

what is your vehicle?


----------



## daniel_bergamini (Aug 25, 2003)

> _Originally posted by EZSnow _
> *what is your vehicle? *


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...

http://www.plowsite.com/showthread.php?s=&threadid=10916


----------



## wyldman (Jan 18, 2001)

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.


----------



## daniel_bergamini (Aug 25, 2003)

*Update.*

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.


----------



## wyldman (Jan 18, 2001)

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.


----------



## daniel_bergamini (Aug 25, 2003)

*SUCCESS! sort of*



> _Originally posted by wyldman _
> 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.


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



> 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.


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?



> 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.


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.


----------



## wyldman (Jan 18, 2001)

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.


----------



## Mike 97 SS (Aug 11, 2002)

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


----------



## daniel_bergamini (Aug 25, 2003)

> _Originally posted by wyldman _
> 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.


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



> 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.


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.


----------



## wyldman (Jan 18, 2001)

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.


----------



## daniel_bergamini (Aug 25, 2003)

*1 pin 2 pin what's the difference*



> _Originally posted by wyldman _
> *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 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.


----------



## wyldman (Jan 18, 2001)

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


----------



## daniel_bergamini (Aug 25, 2003)

*more nubie stuff...*



> _Originally posted by wyldman _
> *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.
> *


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


----------



## wyldman (Jan 18, 2001)

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.


----------



## daniel_bergamini (Aug 25, 2003)

*Ok hard evidence of something.*



> _Originally posted by wyldman _
> *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.
> ...snip...
> Quickly swap sensors,with minimal coolant loss.Top it up,and your done.
> ...


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?


----------



## wyldman (Jan 18, 2001)

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


----------



## daniel_bergamini (Aug 25, 2003)

*1/2 way done.*



> _Originally posted by wyldman _
> *It the 4 pin harness you want.Pin C should be a dark blue wire,Pin D should be a black wire. *


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.



> If women don't find you handsome, they should at least find you handy. - Red Green


----------



## wyldman (Jan 18, 2001)

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.



> If women don't find you handsome, they should at least find you handy. - Red Green


LMAO I'm not that ugly.


----------



## daniel_bergamini (Aug 25, 2003)

> _Originally posted by wyldman _
> *You need to measure voltage at the EBCM side,not the harness side.*


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


----------



## wyldman (Jan 18, 2001)

The EBCM or electronic brake control module is the black box mounted below the master cylinder.It has two plugs,a 6 pin,and a 4 pin.The 6 pin is all the power,grounds,and inputs,the 4 pin is to control the anti-lock valve.If you disconnect tht 4 pin connector at the EBCM,you must measure on the EBCM side,right at the pins.

If your going to measure right at the EBCM,then disconnect the 4 pin connector,and leave the 6 pin connector in place,so the module has power.It probably easier to just pull the 4 pin connector off the anti-lock valve,and measure between the blue and black wires there,with the key on.


----------



## daniel_bergamini (Aug 25, 2003)

*ok got it*



> _Originally posted by wyldman _
> *If your going to measure right at the EBCM,then disconnect the 4 pin connector,and leave the 6 pin connector in place,so the module has power.*


Ok took off the 4 pin connector and measured between pin 3 & 4 inside the EBCM. Got 0, zip, nada volts. Anything else I can try?


----------



## daniel_bergamini (Aug 25, 2003)

*temperature.*

So beyond the success in getting the temperature gauge to move this morning, the temp still likes to hover around a hundred but at least the gauge likes to bound around 100 now. What temperature should I be seeing?

It's a nice 75 degrees here today, pretty dry with a little breeze. I am getting the feeling I should have replaced the thermostat when I swapped the new radiator and hoses in... la-z-boy.


----------



## wyldman (Jan 18, 2001)

That truck should be 180-200 degrees on a warm day.Sounds like the thermostat may need to be replaced.


----------



## daniel_bergamini (Aug 25, 2003)

*Sorry about all the newbie stuff.*



> _Originally posted by wyldman _
> *That truck should be 180-200 degrees on a warm day.Sounds like the thermostat may need to be replaced. *


What temperature thermostat would you run? For now the truck will see a decent amount of highway travel, but then it will sit for a while and only be driven locally.

Are we at the point where I give up on the brakes and bring it to someone who knows that they're doing? Clearly I do not. Was 0V an indication that the ECBM is blown and you don't have the heart to tell me?

Thanks again.


----------



## wyldman (Jan 18, 2001)

Always run a hot t-stat,especially in a fuel injected vehicle.A 195 or 198 degree is what you want.Anything less and you will pay for it in economy.

If you have 0 volts coming out of the EBCM on pins C and D,then the EBCM is bad.To make sure you measured it right,plug both the 6 and 4 pin connectors into the EBCM,and unplug the one 4 pin at the anti-lock brake valve.Check on the black and blue wires,with the key on.Again,less than 4 volts,and the EBCM is bad.If you have more than 4 volts,it's the anti-lock valve.You could save some $$$ and get a used one if need be.

If you want you could go back through our earlier discussions and double check everything we did so far.If you need and more diagnostic info,let me know.


----------



## daniel_bergamini (Aug 25, 2003)

> _Originally posted by wyldman _
> *Again,less than 4 volts,and the EBCM is bad.*


So I had it at the shop and for grins I asked them to troubleshoot the issue and they came up with the same thing EBCM is bad. Anyone know the part number and a place to buy it from (used preferably or otherwise)?


----------



## wyldman (Jan 18, 2001)

Part number should be on a sticker on the outside of the black box.If not,the dealer should be able to look it up for you.

Any good wrecker should have one,and hopefully they won't want too much for it.


----------



## Mike 97 SS (Aug 11, 2002)

I wouldnt put a used one, not a part like that, just my oppinion. Around here, if you buy an electrical part used and it goes bad, they dont wanna know nothing at the junkyard where you bought it, which I guess is kind of understandable. The thing is this, they may want $50 for the used one, maybe the new one costs $100, just an example. To me the extra $50 spent is worth it to go new. The new one will have some kind of warranty also, the used one will not. Just something to consider. Mike


----------



## wyldman (Jan 18, 2001)

I woudn't hesitate to go used,as new can be very expensive.They very rarely fail,so the odss of getting a good used one are pretty good.As long as you buy from a reputable place,you should be fine.


----------



## daniel_bergamini (Aug 25, 2003)

I'm leaning toward rebuilt, where would you guys go online in that case? Getting around to junk yards gets harder and harder every year.

I found a few places that sell the A-1 Cardone brand; buyautoparts.com sells it for about $65 (not including $20 core)and autozone.com (leaning toward because they're local and it makes the core easier) for $73 ($24 core).

Anyone have other options. I figure for the money, it's not going to get too much better. Thanks.


----------



## wyldman (Jan 18, 2001)

I wouldn't go rebuilt.While I haven't ever used a rebuilt brake EBCM,I have used a few engine ECM's,and they all gave me problems.


----------



## wyldman (Jan 18, 2001)

Do you have any numbers off your old one ? I have one here that you can have,only cost is shipping.Shouldn't be more than $20.00-30.00 dollars to ship if you want it.


----------



## daniel_bergamini (Aug 25, 2003)

> _Originally posted by wyldman _
> *Do you have any numbers off your old one ? I have one here that you can have,only cost is shipping.Shouldn't be more than $20.00-30.00 dollars to ship if you want it. *


Wow, that's awefully generous, thanks. I'll check when I get home - the truck is in the shop (again) having some ball joints replaced and yet another alignment. Is it a common problem with older trucks (1991) with a little oversized tires (31x10.5x15lt) to have the wheel be off center after an alignment? This has happened 2x now, and I'm not really happy about constantly having to bring it back.


----------



## wyldman (Jan 18, 2001)

If your sure the toe is correct,you can center the steering wheel yourself quite easily.Just loosen off the clamps and turn the adjusting sleeve between the pitman arm and the steering block,behind the drivers side tire.Try a little at a time until you get it where you want it.It won't affect the actual wheel alignment at all.


----------



## daniel_bergamini (Aug 25, 2003)

> _Originally posted by wyldman _
> *It won't affect the actual wheel alignment at all. *


Well that's good to know. Now all I have to do is figure out what an adjusting sleeve, pitman arm and steering block are and I'll be all done running defenseless grandmothers off the sidewalk.

I'm sure it will be pretty straight forward when I look at how the front end is all connected. Thanks again.


----------



## wyldman (Jan 18, 2001)

Here is a pic looking into the drivers side wheel well.The adjusting sleeve is what is outlined in red.


----------



## daniel_bergamini (Aug 25, 2003)

> _Originally posted by wyldman _
> *Do you have any numbers off your old one ? I have one here that you can have,only cost is shipping.Shouldn't be more than $20.00-30.00 dollars to ship if you want it. *


It's the kind that mounts to the BMC. It has 6 wires on top and 4 on the bottom. It had what I believe to have been a huge barcode at one time - which hasn't weathered well and a label with SZ0941 on it. Hope this helps - you have the right one and let me know how you would like payment. Thanks much.


----------



## wyldman (Jan 18, 2001)

That's the number.This one is different,but still may work.Let me check with GM,and see if they can cross it over or not.

As far as payment,I don't want anything for the ABS controller,it yours for free.Just pay the shipping.It may be easier if I give you my info,and you go to UPS\Purolator,etc and tell them you want a package picked up and shipped to you.Probably cheaper,and no exchange rates to worry about.

I'll get back to you ASAP if this one will work.


----------



## daniel_bergamini (Aug 25, 2003)

> _Originally posted by wyldman _
> *I'll get back to you ASAP if this one will work. *


The suspense is killing me...:crying:


----------



## wyldman (Jan 18, 2001)

Sorry it took so long,it's been a busy afternoon here.

According to GM,it will not cross over by part number.That's no guarantee it will not work,just they don't recommend it.

I'm going to see if I can find a 91 truck with the same box as your,and swap it out and see.If it works,it's all yours.Just don't want to ship it all the way there,and find out it won't work.


----------

