91 3fe erratic CDL light (1 Viewer)

[Arjuni]

Hey yall, first a quick thank you for all the knowledge being shared on this site.
I just recently bought my cruiser and I do not think I would have pulled the trigger if it wasnt for the confidence that this amazing resource that is IH8MUD instills in me.

I have a 91 fj80, bought it with 160xxx miles and loving it.

Now then, onto the matter at hand...

I bought the truck with the CDL lamp always illuminated, even when the CDL is not engaged. I know it is not engaged permanently because I can press my CDL dash button, here a click, and when I turn the tires on pavement it sounds REAL crunchy. Then I press the dash button again and smooth turns. The light stays on the whole time.

So, not a big deal, it was something I was planning on fixing down the line. But recently I got a new set of cats installed and after the fact I noticed two things: one, my check engine light is now on and two, the CDL light turned off.

A minor victory and a minor setback, I thought to myself. Turns out not so much. A day later the CDL light turns back on. And then the next day it is off. And then on again...

Heres the bad part: now every so often when I start the truck the CDL light is on (im used to that by now) but THE CDL is actually engaged! By itself. Also, it gets stuck and I have to roll in neutral to disengage it. (that took me a minute to discover)

So, long story so far, but basically I have no clue why my CDL is engaging by itself on startup every so often. I bought this thing as a DD for the wife and I really don't want this happening to her at a random time during the day.


I have done LOTS of research on the forum, and am getting myself acquainted with the CDL system, but there does not seem to be much info on my problem. Everybody is testing things out on the CDL system because they cannot get it to engage. Mine engages just fine, granted now it is getting stuck... But the issue of the light coming on and off while not actually engaging the CDL is strange.. And then it randomly engaging on startup, I cannot find any similiar issues.

So, any help people? I know there are some real committed cruiser heads here, and I would love some input if anyone is inclined.

THANKS!

Oh yeah, the check engine light was code 28, and Ive got some denso O2s in the mail. Makes sense considering the mechanic took the old ones off and on again to put in the new cats. What that has to do with my CDL light I have nooooo idea.

My thinking after lots and lots of research is that maybe I have a bad ground and the switch is triggering because of that? I dunno..... Current plan to keep the wife on the rode with no hiccups is to wait until the light goes off, which seems to happen randomly on some startups, and pull the plug on the transmission relay, and take out that 30 amp fuse. Maybe then at least the CDL cant engage? Maybe pull the plug on the switch/sensor on the transfer case also? Please correct that logic if I am wrong on that, but it is my best quick fix idea right now.

 

[ppc]

A 91 model is should have a dash switch to engage/disengage the CDL and also the CDL will be enabled when shifting into low range. Disconnecting the 4LOW sensor on the transfer case would be a starting point but you need to also look at other possibilities as well. It appears to be an electrical issue so you need to determine what modifications or repairs you or the previous owner that would impact the wiring. Things like installing a new radio, new lights/bulb etc. The CDL dash light seems to be a separate problem as that is a completely different circuit from the CDL actuator. There is a good chance that is caused by the wiring harness to the CDL sensor shorting to ground. The exhaust/cat work could have moved that harness temporarily eliminating the short.

 

[Mixelplix]

I would also change the transfer case fluid. While it likely won't solve your issue, it made the CDL operation on my 91 much more quick and predictable.

 

[Arjuni]

Thanks for the replies guys.

Yes I have the cdl button on the dash. It works, too.

Looks like a transfer case fluid refresh is on my list now.

So do you think I am right in thinking that if I just disconnect the transmission relay the cdl will no longer be able to engage ? Or would the switch/sensor be what turns it on and off, I am a little unclear on this.

Also, what is powering that pesky cdl lamp? I tried taking out the 30amp fuse, the 10 amp above it, the tranny relay, and even disconnected the switch/sensor on the transfer case itself, but the dang light stayed on.

But I did replace the o2 sensors with success today. No more cel lamp! It was a little funny down by the o2s, one of them was spliced in. Really badly. Maybe this kind of work from the PO has something to do with the cdl kicking on randomly? I’m a little concerned that the electrics are all like this... by the transfer case next to the cdl censor/switch there was an odd disconnected dangling wire with a connector that looked similar but not identical to the cdl censor/switch...

 

[ppc]

In a properly working system either the dash switch or the 4Low sensor switch will activate the locker. Did you try disconnecting the wire harness to the 4Low sensor? It is the connector on the rear extension of the transfer case at the 1 o'clock position looking to the front of the vehicle. You could disconnect the transmission relay but why not do some diagnostic trouble shooting before you do that. Living in KC it might be helpful in slippery road conditions to be able to lock the CDL.

The CDL dash light is powered by a 10A "Gauge" fuse not the 30A. What connector did you disconnect? The correct connector is on the front passenger side of the transfer case. Power is connected to one side of the dash lamp and the other side of the dash lamp is connected to the sensor switch and then to ground. If the wire from that dash lamp to the switch has a path to ground the light illuminates. It should be easy to diagnose the problem, Download a copy of the FSM and follow the wiring diagrams in the back to determine wire colors, paths and connectors.