CDL engages, no light for rear locker - front engages normally. Question on getting rear working. (1 Viewer)

[Novaphotog]

So testing my virgin lockers on some gravel. CDL / ABS lights come on and feel it engage in 4L (no CDL switch yet). Push and turn for rear locker (hear ECU relay click to my right) no blinking light on dash.

Can’t really hear actuator.

Turn switch for front - blinks and locks right up solid and wheel gets hard to turn.

Can the front lock without the rear working? And what would cause the light not to at least blink even if the actuator was the fault (burned out?)

 

[LandLocked93]

Can you confirm the rear is not locking through the abscence of that which normally happens when driving a locked axle vehicle on pavement?

It would take intentional fettling of the OEM circuitry for the front to lock with the ECU also knowing the rear has not.

And...when you say "virgin lockers"...please elaborate.

 

[ppc]

Front can lock independent of the rear. The only requirement is that the center is confirmed locked by the illumination of the CDL dash light.

The rear not flashing could be a burnt out bulb in the dash, malfunction of the diff lock ECU, a bad wiring harness or dead locker actuator. First thing I would try, removing the plug on the rear sensor switch, short the terminals together to see if the dash light illuminates. After that would listen for relays clicking as you rotate the locker switch.

 

[Novaphotog]

Can you confirm the rear is not locking through the abscence of that which normally happens when driving a locked axle vehicle on pavement?

It would take intentional fettling of the OEM circuitry for the front to lock with the ECU also knowing the rear has not.

And...when you say "virgin lockers"...please elaborate.

Will need to confirm (jack truck up and check).

And “virgin lockers” aka I just bought the truck from someone who I’m pretty confident never used them.

 

[Novaphotog]

First thing I would try, removing the plug on the rear sensor switch, short the terminals together to see if the dash light illuminates. After that would listen for relays clicking as you rotate the locker switch.

can you elaborate on this exact procedure and location of said terminal?

talking about the connection back under the truck at the locker?

Might also be good to clean out these connections haha

 

[ppc]

Yes, I'm referring to the connector to the sensor switch near the actuator on the rear axle. On the US vehicles it is on the passenger side of the rear axle under a protective bracket. There are a number of older threads you can search for pictures and explanations on how to debug. The FSM is also going to be very helpful for debugging the problem. An electronic version can be downloaded from this forum.

 

[Novaphotog]

Can you confirm the rear is not locking through the abscence of that which normally happens when driving a locked axle vehicle on pavement?

So yesterday when doing driveline fluids, I had the truck jacked up and was able to confirm (by spinning the wheels) that the rear locker is not working. Had a friend listening for the actuator and moving the wheels after engaging Low range and CDL.

Nothing. No blinking dash light, no sounds from passenger side area, no movement of the actuator.

Front locked up just fine. Light blinked, relay noise from passenger side, actuator engaged, light went solid.

It was towards the end of the day, so I didn't get a chance to pull/clean the connections in the rear, but would that cause the above symptoms? Particularly, the lack of blinking light in the dash...I'd think a dirty switch at the actuator would at least have the ECU "attempting" to lock.

 

[ppc]

No light on the dash would indicate a problem other than the a bad sensor on the rear axle. It could be a problem within the locker ECU, wiring to the rear actuator or within the actuator itself. There are small limit switches within the actuator that could have been damaged by water intrusion. There are a couple of threads related to rebuilding the actuator that would help to guide you.

 

[LandLocked93]

So yesterday when doing driveline fluids, I had the truck jacked up and was able to confirm (by spinning the wheels) that the rear locker is not working. Had a friend listening for the actuator and moving the wheels after engaging Low range and CDL.

Nothing. No blinking dash light, no sounds from passenger side area, no movement of the actuator.

Front locked up just fine. Light blinked, relay noise from passenger side, actuator engaged, light went solid.

It was towards the end of the day, so I didn't get a chance to pull/clean the connections in the rear, but would that cause the above symptoms? Particularly, the lack of blinking light in the dash...I'd think a dirty switch at the actuator would at least have the ECU "attempting" to lock.

Do both locker lights light up when you turn the key to ACC or Run? Does either one light up? If only one, and it's the front one, you might have a dead bulb in addition to other things (obviously). But a working bulb is helpful for t-shooting.

 

[Novaphotog]

Do both locker lights light up when you turn the key to ACC or Run? Does either one light up? If only one, and it's the front one, you might have a dead bulb in addition to other things (obviously). But a working bulb is helpful for t-shooting.

I only see one red diff lock light at ACC/Run (the front). Is the signal to flash both at ACC/Run coming from the same source (locker ECU)?

 

[Novaphotog]

Downloaded a copy of the FSM...this will help haha!

 

[LandLocked93]

Downloaded a copy of the FSM...this will help haha!

View attachment 2215813

Good deal.
So I suspect you would see a blinking rear locker light all the time (when attempting to lock the rear), were the bulb for the rear locker light confirmed good.

From there, I would start at the t-case sensors and work toward the rear actuator. If you hear nothing when attempting to lock the rear, could be the actuator isn't getting power or isn't getting the lock signal from the t-case sensors. (pardon my 'relative' terms). The FSM should have an entire t-shooting section for it.

 

[ppc]

With the front locker engaging properly that means the sensors on the transfer case are properly working as is the CDL.

 

[Johnny Boy]

I have the same issue (rear diff blinking but diff not locked - CDL + Front diff OK).
- tried with another Diff ECU --> no change
- tried to power directly the rear actuator --> OK, it works without issue

So now I guess I have an issue with wiring.

 

[Novaphotog]

I have the same issue (rear diff blinking but diff not locked - CDL + Front diff OK).
- tried with another Diff ECU --> no change
- tried to power directly the rear actuator --> OK, it works without issue

So now I guess I have an issue with wiring.

At least yours is blinking haha! Update here with what you try wiring wise, very curious, and glad I'm not alone in the world!

 

[Novaphotog]

The FSM should have an entire t-shooting section for it.

Yup!

 

[Johnny Boy]

At least yours is blinking haha! Update here with what you try wiring wise, very curious, and glad I'm not alone in the world!

Did you already powered on directly your actuator ?
Maybe check your wiring too. Mine (trailer wiring loom, located driver side as RDL wiring loom) was a bit burned when I purchase the vehicle.
So I guess other wires are damaged too...

 

[Novaphotog]

Did you already powered on directly your actuator ?

No, did you remove it and bench test it with a battery? Or how did you test?

 

[Johnny Boy]

As your front actuator is working fine (dashboard+actuator), remove the rear actuator (not a big job with fsm) and hook it up to the front wiring. If it works, you can refit the actuator and start to check the wiring. If it doesn't works, you can start to open/repair the actuator (btw actuator o-ring is dead very often and so the risk of water that can go in increase)

 

[Johnny Boy]

FYI, issue solved for me. Wiring failed at 2 different spots :

- Diff wiring :

- Rear quarter panel wiring (wire was still in the plug, but not enough plugged) :

Now rear diff works perfectly.

However still one bad news : combination meter bulb from front diff has just failed (front diff works, but no bulb on at contact or when front diff is on )