What is this......

[MojaveJoe]

What is this... and where does it go?



Found it hangin loose under the hood near the brake master cylinder.

Looked all over but couldn't find a place where it plugs in. It's a tiny printed circuit board with an apparent sensor on one edge (?)



Need help figuring out what it is, and where it should be plugged in?



All advice and experiences welcome.



Joe

 

[rbattelle]

I think you're going to have to post a photo.

Ryan

 

[MojaveJoe]

Yep... forgot it had to be trimmed down to 400x400 pixels.
So ..... ? What do you think?

 

[rbattelle]

Did you buy that truck used? It looks to me like some kind of fooler device.

Could it be the battery temp sensor?

I'm going outside to do a couple things on my truck. I'll take a look for something similar.

Ryan

 

[Gary - K7GLD]

Looks like an outside air temperature sensor - dunno about the 3rd generation stuff, but the 2nd gennies have it mounted up on and behind the grille...

 

[MojaveJoe]

Bought truck new in Sept 03 in OH.



The wires attached to it are very short... maybe 12". Come from wiring harness on firerwall. Won't stretch forward any more than in the pic, by the brake reservoir.

 

[Gary - K7GLD]

Wonder if it could be a temperature control sensor for the heater? Any heater box or ductwork in that area? The battery temp sensor on my '02 looks NOTHING like that... I doubt it's any sort of IAT sensor...

 

[rbattelle]

This one looks close. But mine has a dead-end plastic connector on it instead of the open circuit you've got.



Mine is clipped to another wiring harness and sits just in front of the clutch master cylinder. I have nothing where you found yours. They could still both be the same connector, but your truck is a later build than mine (so the connector shape and position may have changed).



That could mean you simply lost the little cover. (I didn't pull my cover off to see what was under there).



Then I was thinking maybe yours is the brake fluid level sensor? But if it were I'd expect all your brake fluid to have leaked out.



Ryan

 

[TCDiesel]

Ryan, Why have you NOT wire loom those wires , the one's next to the C130 are going to cause you Trouble some Day

 

[Mindbndr]

Battery temp sensor. I also had mine come out on my 06. There should be a hole under the battery box for it. If you take out the battery you will see a little spring loaded disc from the top. If you twist the disc the little assy comes out. I had to glue mine back in bacause the plastic that heald it in actually broke.

 

[MojaveJoe]

Good try Mindbndr... . but my battery sensor is still installed properly.

I removed the circuit board component from the wiring harness. On closer inspection I noticed a broken plastic edge going around the circuit board on the base connector. So apparently there was a skinny plastic cover over the circuit board. Maybe it was hanging loose in the engine compartment to sense outdoor temp? I checked my ambient temp gauge in the overhead console with it removed but it still reads 52F.

Here are a couple more closeup pics of the component and its harness connector. Remember, this component probably has a thin black plastic cover on it, normally, and is generally found between the brake fluid reservoir and the driver side fender.
One last note. . The Parking Brake light on the dash stays on all the time with it removed, but the truck runs and brakes fine. Reinstall component and light goes out.

 

[CJ Johansson]

You say the parking brake light comes on with it removed, and out with it plugged back in. With it in, does the parking brake light come on when you put on the parking brake?

Just looking at the board, the little glass thing on the edge looks a lot like a magnetic reed switch. They actuate when you put a magnet next to them. The circuit looks like there are only 2 pins, with the glass switch connected across them.

My guess is that this is the switch used for sensing when your parking brake is on. Of course, if your brake still turns on the light, I'm wrong.

-cj

 

[MojaveJoe]

Good thought CJ

I tested the Parking Brake Light function. Here are the results:

Component installed... engine running
Parking Brake off... . Light off
Parking Brake on... . Light flashing

Component not installed... engine running
Parking Brake off... Light on
Parking Brake on... . Light on (not blinking)

Is it possible this is the "Brake Lamp Switch"

 

[Semicrazy]

Brake FLI switch? (Brake Fluid Level Indicator Switch?)



Most brake resovoirs use something like a magnet on a float so as the fluid drops and the magnet get close to the FLI switch is causes your brake light to come on.



The FLI circuit board is generally encased in a plasitic housing that snaps into the resivoir, but it is sealed off from fluid so that you can replace it without fluid leaking out.



Most newer resoviors when you shake them you can here the magnet rattling back and forth.



Well that is my guess from what you have described, the location, and what happens when you unplug it.



Edit, on second look at your additional pictures it sure does look like the FLI switch and the plastic housing broke off at the base of the circuit board. Check to see if the oval/pencil shape housing is still snapped into the middle of the base of the resovoir. Or if there is a spot for it in the base of the resorvoir but it is missing the FLI switch. It just has two little finger on the passenger side of the base of the resivoir that you squeeze and the FLI switch will pull out on the drivers side. The electrical connector is on the drivers side.

 

[Semicrazy]

I could not find a good shot for 2500/3500 but here is a 1500, same thing though.

 

[rbattelle]

If it's an FLI switch that's magnetically triggered, then you should be able to test it by bringing a magnet close to it, right? Try that.

Ryan, Why have you NOT wire loom those wires , the one's next to the C130 are going to cause you Trouble some Day

I'm so embarassed. In my defense, 90% of the length of those wires is in a shielding (polyethylene sleeve). What you're seeing is the last foot or so as they branch out from the sleeve and go to their respective components (mostly fuel system).



Also, that's SXL cross-linked polyethylene insulation on those wires. Not your usual stuff. Operable from -49°F to 257°F and resistant to all fuels, oils, most acids, and most solvents. The sleeving I use is made of the same material.



Of course, the lack of a covering means they're prone to abrasive damage, but I've carefully routed them and wire-tied them to help prevent that.



Ryan

 

[Slingblade]

That goes to the master cylinder like semicrazy posted. It's the same as on my '04. I didn't unplug just looked at the connector. Same year of truck should be the same connector.

 

[MojaveJoe]

Semicrazy... isn't all that crazy it seems :-laf

I went to the dealer and after a half hour searching the computer and talking to the techs in the shop we determined the same thing. See pic below of location on drivers side of reservoir where the component broke and fell out. The dealer said I had to buy the reservoir too. But if I can get the black plastic cover out of the reservoir we'll see what he says then.

If he still insists I have to pay $79 for the reservoir with the switch... well I'll just stand there and Oo. until he changes his mind.

Or maybe I'll just super glue the cover back on and reinstall it in the reservoir. I will post my progress and findings.

(I vaguely recall working in that area and hearing something plastic go *crack* a couple years ago. Never could locate the broken part... but I bet this is it. )

Thanks for all your help guys.
Joe

 

[rbattelle]

If he still insists I have to pay $79 for the reservoir with the switch... well I'll just stand there and Oo. until he changes his mind.



Or maybe I'll just super glue the cover back on and reinstall it in the reservoir. I will post my progress and findings.

Is it really worth it? I mean, this thing is simply meant to light up the brake light if your fluid runs near empty. What are the chances?



You've lived fine with it for this long, why fix it? If it were me, I think I'd just glue it back in place and call it a day.



Ryan

 

[MojaveJoe]

I was just kidding Ryan... I will test the old one to make sure it still works, and glue it back together if it is working. If it doesn't work right, and it is removeable... it will probably be available by itself.
I'll try to remove the sleeve from the reservoir tomorrow.
Regards,
Joe