CDL Will Not Engage....

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WarWagon

WarWagon

10 Year
Joined
Dec 8, 2013
Threads
282
Messages
1,476
Location
North GA
Very frustrated; my CDL light/center diff has never come on or engaged, hence neither front or rear locker will engage. Replaced the 1 o'clock position sensor switch today with a new one and still no go. To my knowledge this one controls the light? Could it be I need to replace the other 2 o'clock position switch as well? If do does anyone have the part # of the other switch? It's a different connection than the one on top of the tcase.

Thanks
 
CDL sensor/switch is:

cdlzoom.jpg


Simple test is to meter the switch while it is out, should go zero ohms when pushed in, infinite ohms when released.

With switch out, put a wire link across the connector (as if the switch was pressed in), you should get the CDL light to come on (as well as the ABS), if not, you have issues with the bulb, the harness, the connector etc...

What have you tried/tested so far, or did you just replace the switch in the hope it would fix things?

cheers,
george.
 
Also, have you listened to hear if the CDL actuator is actually engaging? With engine off, ignition switch to ON, you should hear the CDL actuator cycle when you engage/disengage the CDL.

Do you have the dash switch? Done the pin 7 Mod? Or just using the low range lever?

More info...

cheers,
george.
 
Are you using a button to engage the CDL or relying on the transfer case being in 4Lo?

If the ignition is on, even without the engine running, when you either hit the button or if you haven't done the pin-7 mod, you should hear a click coming from a control box near the lower driver's door hinge. This relay box is what actually powers the CDL actuator.

The way I'm reading your post, you say you get no light AND that it won't engage. How have you tested that it won't engage?

If the parking brake is not engaged, transmission is left in Neutral, the transfer case in either 4Hi or 4Lo, and the CDL UNLOCKED, if you jack up a single tire you should be able to spin it. There will be resistance due to the viscous coupler, but the combination of the differential in whichever axle you are using and the center diff, plus the transmission being in neutral, should let the tire keep spinning (again, with resistance).

Same test with CDL engaged, there will be some play but that tire will stop dead.
 
I simply replaced the switch, haven't done any tests yet. I have a '97 and haven't done the mod switch so I'm relying on the 4L to engage the CDL. No CDL light ever comes on. And of course when I engage my front and rear lockers the lights only blink.
 
Yep, well, you've done nothing other than spend money on a switch/sensor that may have been just fine.

Now do the other tests as per above, then report back.

cheers,
george.
 
I switched out the bulb when I did all the other dash lights. And the switch was only $18 so I figured it was worth a shot in the dark. But previously, even if the bulb was out shouldn't it still have engaged?
 
Just went outside and engaged 4L....I can here the clicking next to the DS floor panel so I assume the CDL is engaging. Yet when I flip the diffs they only blink.

When I put it in 4L I don't see CDL or ABS lights.
 
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Click is a relay. You should hear the actuator (motor) it will make a short buzz kind of sound as it cycles to engaged and again when it cycles to disengaged. Takes a second or two to cycle each way. You need to be in a quiet place to listen for it or have a helper cycle the 4L lever as you listen under the vehicle.

If you don't hear the motor sound, then the CDL is not engaging/disengaging.

cheers,
george.
 
A few things have to happen for everything to operate appropriately.

"CDL switch" in dash or 4Lo signals relay to engage
relay engages telling actuator to engage CDL motor (click is the relay)
motor runs to move the actuator (whirring/electric motor sound from transfer case)
once teeth line up you might hear a click or snap from the transfer case as the CDL actually engages
AFTER it is engaged (not necessarily when the motor runs, see note below) the fork should depress the "CDL INDICATOR switch" as shown in a picture earlier in this thread
That switch gives ground to complete the circuit to the dash light and FR/RR diff lock computer

Note that the actuator has a spring in it.. if the teeth of the CDL aren't lined up, or if already engaged and you are trying to disengage with tension between the front/rear drlivelines the motor still cycles but pushes against this spring, and once teeth do line up, or tension between front/rear drivelines is released it'll snap in or out. "out" can be a pretty loud bang if you are driving

What very often happens with these rigs is the CDL actually engages, but the indicator switch won't work properly, so you get no dash light, and no diff locks if appropriately equipped. It has been suggested that the cause is this indicator switch not getting enough current to help self-clean the contacts inside it, since it was originally designed to handle the amperage from reverse lighting on manual transmissions. Especially when you consider how infrequently the average FJ80 has the CDL engaged.

In my case I was able to fix my non-operating switch by giving it a very quick blip of current from the battery. Worked fine after that.. for a few months, now it is dead again.

In your case, your CDL may not be actuating in the first place.

There is plenty in this thread on how to diagnose most of your potential problems.
 
I did a CDL switch and 7pin in my '97 and it worked right out of the box (garage). Flash forward three years and after a few months of not responding to the switch (on or off) now I get no locking, and no lights. AND no lights or locking even in 4-Low! That always worked before!
 
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JCruse said:
I did a CDL switch and 7pin in my '97 and it worked right out of the box (garage). Flash forward three years and after a few months of not responding to the switch (on or off) now I get no locking, and no lights. AND no lights or locking even in 4-Low! That always worked before!
Click to expand...

Once you have done the mods (CDL switch and pin 7 mod) the switch is the ONLY thing that will engage the CDL, 4-Low lever will no longer automatically engage the CDL.

So, have you PROVEN that the CDL is not engaging (listened for the actuator) and jacked up the vehicle to verify engagement?

The CDL dash light (and abs light) are ONLY lit due to the CDL sensor/switch on the transfer case. So, even if the CDL actually engages, if the switch/sensor is faulty/dirty etc and doesn't go zero ohms when pressed in (by mechanical dodads in the CDL guts) then the lights on the dash won't light up... even though mechanically the CDL has actually locked.

cheers,
george.
 
WarWagon said:
Just went outside and engaged 4L....I can here the clicking next to the DS floor panel so I assume the CDL is engaging. Yet when I flip the diffs they only blink.

When I put it in 4L I don't see CDL or ABS lights.
Click to expand...

When working on stuff, it good to understand how it works and this system takes a bit to get your head around. This thread has good discussion, posted the explanation from the NCF starting here: CDL Actuator Fun
 
george_tlc said:
Once you have done the mods (CDL switch and pin 7 mod) the switch is the ONLY thing that will engage the CDL, 4-Low lever will no longer automatically engage the CDL.

So, have you PROVEN that the CDL is not engaging (listened for the actuator) and jacked up the vehicle to verify engagement?

The CDL dash light (and abs light) are ONLY lit due to the CDL sensor/switch on the transfer case. So, even if the CDL actually engages, if the switch/sensor is faulty/dirty etc and doesn't go zero ohms when pressed in (by mechanical dodads in the CDL guts) then the lights on the dash won't light up... even though mechanically the CDL has actually locked.

cheers,
george.
Click to expand...



I haven't jacked it up but there is no sound and no resistance in turns. In 4-Low, switching the diff button makes no difference. I'm thinking of undoing the 7-pin mod to at least give me back locking in Low.

Could the pin-7 mod somehow cause my problems? Like through corrosion or the like? The truck does spend a good 20-30 hours a week on the beach, not counting overnight stays..









.
 
JCruse said:
I haven't jacked it up but there is no sound and no resistance in turns. In 4-Low, switching the diff button makes no difference. I'm thinking of undoing the 7-pin mod to at least give me back locking in Low.

Could the pin-7 mod somehow cause my problems? Like through corrosion or the like? The truck does spend a good 20-30 hours a week on the beach, not counting overnight stays..
.
Click to expand...

CDL doesn't really affect turning too much (your axle diffs are unlocked...). There can be a bit of drive train windup on dry pavement, but on wet roads, sandy roads etc you'll barely notice it. Do you hear the CDL actuator cycle (engine off, key to ON) when you press/release the dash mounted CDL switch?

Pin 7 etc just changes where the signal comes from to engage the CDL actuator, so going back to it activating only via 4L won't make much difference electrically/wiring-wise.

The CDL system is pretty simple and debugging it isn't a big deal, IF you follow some basic steps. Tools-r-us's link above is a good start to how the system works.

cheers,
george.
 
When I engage 4L I hear the click of course and what appears the be a very slight motor engagement. Hard to really tell though. I swapped out the sensor switch a couple of days ago so I don't think it's the switch. What's the other switch next to the CDL sensor switch? I pulled it to clean and noticed outside of the plug in being different it's basically the same switch.

Minus the lights, if the CDL was engaged wouldn't that lock the lockers and make the diff lights solid?
 
The CDL sensor switch is not on the rear extension of the transfer case. It is located on the front extension. What you replaced was the L4 Position Switch which senses when you shift to low range and triggers the CDL to lock. If the pin 7 mod is done this switch has no effect on the CDL but only changes the shift points on the transmission. The other sensor switch on rear extension is the Neutral Postion Switch which lights the AT/P indicator on the dash when the transfer case is in the neutral position. Most all of your questions can be answered by downloading a copy of the FSM and reading through it. You will learn many useful things.
 
WarWagon said:
When I engage 4L I hear the click of course and what appears the be a very slight motor engagement. Hard to really tell though. I swapped out the sensor switch a couple of days ago so I don't think it's the switch. What's the other switch next to the CDL sensor switch? I pulled it to clean and noticed outside of the plug in being different it's basically the same switch.

Minus the lights, if the CDL was engaged wouldn't that lock the lockers and make the diff lights solid?
Click to expand...

Simple, if the light DOES NOT LIGHT (assuming bulb is not blown), then the F/R diff locks will NOT engage. The same wire that lights the dash CDL light goes to the diff lock ECU. Also, if the F/R diff locks haven't been used for a long time, they can stick and not engage. FIRST STEP, get the CDL stuff working and ignore the F/R diff locks and their flashing lights for now.

Again, 1st step is to determine if the CDL actuator is actually cycling. If it is not, then the CDL will not engage and the CDL switch/sensor will not detect anything.

I already wrote earlier to put put a wire link to bridge the CDL switch/sensor connector. That 'should' cause the dash CDL light (and ABS light) to come on. If it doesn't then you have a wiring/harness issue from that connector back to the dash/diff lock ecu. If the light does come on then the problem is in the CDL switch/sensor or the CDL actuator etc.

As Phil wrote above, are you actually removing/replacing the CDL switch/sensor or ??? I posted a picture at the top of this thread.

TIME TO START TESTING THINGS... READ THE FSM. READ Tool's linked thread above.

cheers & Merry Christmas,
george.
 
Thanks for the advice guys, and yeah I see now where I switched out the damn 4L switch, which was working fine :bang:

I see why troubleshooting and tracking down this issue is such a headache. I'm looking at the FSM now so hopefully I'll get this figured out sooner than later.

Merry Christmas!
 
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