Front diff lock isn’t engaging

[ppc]

I pulled my dash earlier this week trying to replace bulbs and the center diff light build just won't light up but you can tell its locking because its going into low and the whole truck rises and gets ready

Shifting into low range is purely a mechanical function, nothing electrical to do that. That explains "the whole truck rises". When the CDL locks you will not really feel anything, only possibly hear relays click. That said, in stock configuration the CDL is activated by a sensor switch detecting when the High/Low shifter is moved to Low. Most here will also add a CDL dash switch that performs the same function allowing the CDL to be activated independently in high range.

As I stated previously the CDL dash indicator light is controlled by a second sensor when the CDL actually locks. Key point being the difference between "activated" versus "actually locked".

 

[Mario12345]

If you read the post i provided a linked to, it states that after i got my center locker working my only other problem was with the front locker. And that problem turned out to be a damaged front locker wiring harness. Once i replaced that harness with a used one, my locker started working again.

I will recheck my harness tomorrow I don't think it is the problem because its also happening to the rear but I really hop it is the problem (hand praying emoji) hahahah thank you

 

[LINUS]

IIRC, another way around the whole CDL issue is to do the “pin 7” mod - lets you lock the diffs in HI range.

But again, been forever since I did mine, I ony know how my 80 w/ a CDL switch & “pin 7” mod done behaves.

 

[ppc]

The pin 7 mod allows you to remain unlocked in Low Range. Has nothing to do with locking in High Range.

 

[LINUS]

The pin 7 mod allows you to remain unlocked in Low Range. Has nothing to do with locking in High Range.

My 80 disagrees with you

I lock the rear in HI on alot of boat ramps retrieving.

Or did before buying the Tundra.

 

[ppc]

You lock in high because you have installed the CDL dash switch, not because you did the Pin 7 Mod. When days were old and nights were bold, before CruiserDan documented the Pin 7 Mod the solution to allow an unlocked center diff was to unplug the connector on the 4-Low Position sensor. The negative of doing that is that the shift points of the transmission don't change. In a stock configuration when shifting to Low the transmission shift points increase to a higher RPM. The Pin 7 Mod retains the signal to the transmission control unit but severs the connection to the CDL control unit.

 

[LINUS]

I’ll believe you - the Tundra inheirited the boat duty once bought.
And lately I’m more in the Tundra mods than the 80.
Sadly, the last ~4 times I started the 80, it was ran in place to idle it every week.
-I’d say I don’t **need** it, but damn if I care to sell.

That & between my black 80 w/mods & the 40th having had e-lockers & a CDL switch when I bought it (never did pin 7 on it) -It’s been awhile since I did anything I had to lock an axle.

 

[Mr Cimarron]

You could pull the CDL indicator switch pigtail from the transfer case and jumper the two pins which should make the CDL dash light come on. Then you will be able to test your lockers a bit better.

 

[Mario12345]

You could pull the CDL indicator switch pigtail from the transfer case and jumper the two pins which should make the CDL dash light come on. Then you will be able to test your lockers a bit better.

How do i do that .??? And i think the spot behind the dash board is just broken ... like the spot where the light goes in because it’s burnt up a little back there when i took my dash apart

 

[Mr Cimarron]

How do i do that .??? And i think the spot behind the dash board is just broken ... like the spot where the light goes in because it’s burnt up a little back there when i took my dash apart

Pull pigtail from sensor/switch and connect the two pins on the pigtail connector. Light on dash should then turn on regardless of whether or not the TC is actually in 4WD.

 

[Mario12345]

Check the plug on the firewall. See if you have power at that connector.

Keep working back if not, at least now you know the core prob.

so I checked the actuator with the 9 volt battery test and it worked I guess from the nosies it made.... but now I also removed the harness and checked it and found nothing wrong with it ........... so now I guess the next step is to tear out the radio and start tracing wires **** my life

 

[LINUS]

^^^^^^^^ Find a scrap of wire some ~10’ long & just make a long jumper wire to check the continuity with a real ohmmeter inline.

You can be more surgical about what you take apart than I think you know.

Have you isolated out this is the CDL as has been talked (since I clearly don’t recall what factory settings w/o P7 mod or a CDL switch in place is) - or simply a front locker issue?

**IF** we’re talking just the FR locker (are you getting CDL function / LO range trans case & seeing the RR locker function?) - then really the only thing in the system is power to the rotary switch, then signal to the relay box, then on to each axle.

The relay box is in the PS front kickpanel, you pull the triangle shape that is also the PS FR door threshold & it exposes the relay box for the axle actuators.

But again, -are we still back doing CDL permissives or are we up to it being an axle locker system issue?

 

[Mario12345]

^^^^^^^^ Find a scrap of wire some ~10’ long & just make a long jumper wire to check the continuity with a real ohmmeter inline.

You can be more surgical about what you take apart than I think you know.

Have you isolated out this is the CDL as has been talked (since I clearly don’t recall what factory settings w/o P7 mod or a CDL switch in place is) - or simply a front locker issue?

**IF** we’re talking just the FR locker (are you getting CDL function / LO range trans case & seeing the RR locker function?) - then really the only thing in the system is power to the rotary switch, then signal to the relay box, then on to each axle.

The relay box is in the PS front kickpanel, you pull the triangle shape that is also the PS FR door threshold & it exposes the relay box for the axle actuators.

But again, -are we still back doing CDL permissives or are we up to it being an axle locker system issue?

Hey so from what i know my cdl works .... i put it into low with the shifter then put it into drive i feel the whole truck shift up and it starts driving in low ... but the cdl light doesn’t come on ... i believe it just doesn’t work tho ! And no it’s front and rear lockers both don’t work

 

[Mario12345]

^^^^^^^^ Find a scrap of wire some ~10’ long & just make a long jumper wire to check the continuity with a real ohmmeter inline.

You can be more surgical about what you take apart than I think you know.

Have you isolated out this is the CDL as has been talked (since I clearly don’t recall what factory settings w/o P7 mod or a CDL switch in place is) - or simply a front locker issue?

**IF** we’re talking just the FR locker (are you getting CDL function / LO range trans case & seeing the RR locker function?) - then really the only thing in the system is power to the rotary switch, then signal to the relay box, then on to each axle.

The relay box is in the PS front kickpanel, you pull the triangle shape that is also the PS FR door threshold & it exposes the relay box for the axle actuators.

But again, -are we still back doing CDL permissives or are we up to it being an axle locker system issue?

And no i didn’t do the 7 pin mod

 

[Mr Cimarron]

Did you try jumpering the two pins yet?

 

[Mario12345]

Did you try jumpering the two pins yet?

Which pins on the front locker ... yes abs it sounds like it worked so for some reason it’s not with the switch

 

[ppc]

Of you don't get the CDL dash light illuminated the the front and rear lockers will not lock period!!! The only exception if the dash light is burnt out. As I stated previously you won't feel the CDL lock. Turn the motor off, switch the ignition to on but do not start. Shift from high to low range and listen for the clicks of relays. Report back results.

 

[Mr Cimarron]

Which pins on the front locker ... yes abs it sounds like it worked so for some reason it’s not with the switch

No you want to jumper the pins from the transfer case switch in the photo. The indicator switch is ground activated. The pigtail will have two pins. Connect them to fool the dash light into thinking the CDL is locked.
You can also search “locker anytime mod” to bypass CDL all together but that’s for another day. Keep it easy as possible for now.

 

[LINUS]

Of you don't get the CDL dash light illuminated the the front and rear lockers will not lock period!!! The only exception if the dash light is burnt out. As I stated previously you won't feel the CDL lock. Turn the motor off, switch the ignition to on but do not start. Shift from high to low range and listen for the clicks of relays. Report back results.

I’m coming around to going with the CDL permissive (It’s been awhile since I really have ran my lockers, TBH, that & that concussion I took) - but the big picture is that the CDL/ trans case locker is really accessible unless you’re armored to the hilt under there.

The sensor plug you need to jumper looks just like the 2 pole one on either axle locker, all 3 confirmation switches are the same & interchange.

I will add that IIRC you get both the ABS light to flash as well as the CDL light in the cluster when yu get it working/jumper the plug - both bulbs being burnt out is slim / none. (That is right, yeah @ppc ?? - correct me if I “whiffed” another one.)

 

[GSTMike]

No you want to jumper the pins from the transfer case switch in the photo. The indicator switch is ground activated. The pigtail will have two pins. Connect them to fool the dash light into thinking the CDL is locked.
You can also search “locker anytime mod” to bypass CDL all together but that’s for another day. Keep it easy as possible for now.

Yup when I got my sorry excuse of a maintained 94 from the PO this was the first thing I did in trouble shooting the lockers, paperclip diagnostics! I ended up needing two of the switches which also turn out to be pretty much standard Toyota reverse indicator switches and only $20 at NAPA.