CDL Sensor/switch

george_tlc

 
 
Joined
Sep 17, 2003
Messages
3,741
Location
Sunnyvale, CA
So, I'm sitting in the car waiting for my wife who is yapping to a friend. I have the engine running and figure I might as well "play" with the switches to relieve the boredom...

First one - the CDL dash switch. Click in, no ABS light, no CDL light. Oh great, something to really have to play with... It's late in the evening, so a job for tomorrow.

Today, key in ignition switch on, engine off. Push in the CDL dash switch, relay clicks, CDL actuator whirrs. Check all the fuses, all functional. So, pull the harness of the front xfer box CDL switch/sensor and jumper it across. Turn ignition to on and the ABS light and CDL light are both on.

Ok, must be dead CDL switch/sensor. Remove it with a big spanner and meter it, push in the ball end - open circuit. Tap it on a big vise a few times, meter it, still open circuit. WTF, being an EE I brought my years of expertise into action and put the switch on the vise - with one flat of the hex and HIT the opposing hex side a few times like I meant it with the handle end of the spanner.

Meter it while pushing in the ball end - 0 ohms, release the ball end, open circuit. Reinstall, ABS and CDL lights come on just as they are meant to when the CDL switch is pressed and the actuator locks the CDL.

Here's a couple of pics of the CDL sensor/switch for reference. I'm guessing that since it's a sealed switch and hardly likely to see any contact wear due to high currents that contacts had just oxidized or something like that. Will be interesting to see how long it stays good and if it does fail at some point I'll get a new one and dissect the old one to see what kind of crap contacts are in there.

I've labeled the hex surface that I hit.





george.
 

george_tlc

 
 
Joined
Sep 17, 2003
Messages
3,741
Location
Sunnyvale, CA
Yes - that's the one. The pics in my post are what that switch/sensor (circled in your pic) looks like when removed...

Oh - you call it the 4L switch - it isn't, it's the CDL switch/sensor.

george.
 
Joined
May 21, 2004
Messages
3,589
Location
San Diego
Ok, just double checking, there are 2 of those on the tcase that look identical and some usually test the wrong one.

Just making sure ya got the right one!
 

george_tlc

 
 
Joined
Sep 17, 2003
Messages
3,741
Location
Sunnyvale, CA
Thanks - but I've fixed my CDL problem. I only posted the thread to show what the switch looks like and what I did to 'refurbish' mine...

george.
 

george_tlc

 
 
Joined
Sep 17, 2003
Messages
3,741
Location
Sunnyvale, CA
After testing the 'refurbished' switch several times I noticed it was occasionally flakey. So, figuring it's oxidised contacts and not some other failure mode, I removed the switch/sensor one more time. Meter shows 0 ohms when the switch is fully pressed in, but if pressed in a little, but not all the way in the resistance fluctuates around the 100's of ohms.

So, out with my bench power supply, set to 12V and 200mA current limit and figured that the contacts could do with a slight bit of cleaning. After a few cycles of this, disconnected the power supply and reconnected the meter. Now it goes reliably to zero ohms as soon as the ball end is pressed in beyond a few mm.

I do know that some switches are rated with some reasonable number of mA flowing, this provides a 'cleaning' action to the contacts.

I'll monitor the switch/sensor over the next week (cycling it agressively in the vehicle) and will report back one way or the other.

george.
 

george_tlc

 
 
Joined
Sep 17, 2003
Messages
3,741
Location
Sunnyvale, CA
Just a mid week update. Wednesday (3rd day after 'cleaning' the contacts with some current). The CDL sensor/switch has been rock solid, works every time, whether first time in the morning or during the day. Looks like it's fixed. I'll update again at the end of the week.

george.
 

clownmidget

 
 
Joined
Jul 2, 2003
Messages
2,430
Location
Trumansburg, New York
Well George, glad your "cleaning" worked but I was looking forward to the results of your surgery ;).

Still, I'll have to log this trick in the back of my mind for future reference.
Thanks
Mike R
 

george_tlc

 
 
Joined
Sep 17, 2003
Messages
3,741
Location
Sunnyvale, CA
Well, 1 week later, still works perfectly every time. so I will officially called it FIXED!

Sorry, no surgery necessary. BUT, if someone has a broken CDL sensor/switch that they kept after replacing with a new one I'd be happy for them to send it to me and I can see if the same scheme will 'refurbish' it for them - I'll send it back.

george.
 
Joined
Feb 6, 2015
Messages
259
Location
Out there
Ok, must be dead CDL switch/sensor. Remove it with a big spanner
I'm having the same CDL sensor/switch issue. Or thus I presume since shorting the harness with a paper clip lights up the ABS and diff lock in the dash whereas previously I could not get these lights to glow. (My rig does not have the CDL switch, just high low stick.) Trouble is, I cannot get my spanner/wrench in there to take out the sensor/switch. I went and bought a 27mm spanner, is this not the right choice? The handle is too damn long to get any leverage, if I can even grip my target with the wrench. Any suggestions for accessing and removing the CDL sensor/switch?
 
Top Bottom