Rear diff lock not engaging

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Oct 11, 2010
Calgary, Canada
Vehicle is a 98 LX470 with factory rear locker
Rear diff actuator is the same as any locked 80
Dash switch is the same with the exception of the FR position

Current issue is that I'm getting only 8.43V at the rear locker actuator and I'm guessing is not enough for it to operate.
- Rear actuator was bench tested cleaned and greased by reputable shop in Edmonton.
- Famous wiring harness from actuator & rear ABS sensors over the frame to main body harness was replaced with new OEM
- Connector from body harness to new rear diff lock harness also getting 8.43V
- Center diff lock operates perfect in HI & L
- OEM locker switch is also New
- When hitting the rear locker switch, ABS light goes on, rear diff lock blinks and the relay clicks on the passenger side area
- Diff lock fuse under the divers side kick panel fusebox is also good
- Like the 80, the 100 has to be in low range with the center locked in order to operate the rear locker

I'm not sure what to check next
Where is the next connector (back to front) that I can measure Voltage?
What voltage I should be getting at the actuator plug?
My next thought was to check voltage at the ECU but unsure how to due that is only one plug coming into it
Looking at this diagrams from the 80 Series it seems that 3 wires come into the ECU and 4 come out. If I understand this correctly, I should get from 9V-14V coming out of the ECU towards the lock actuator in order for it to work?




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I found some diagrams from the 80 Section.
Would this be similar for ours?
With the engine off and things as quiet as possible you should be able to hear the RDL motor move when you turn the RDL switch ON. Roll down the passenger side windows too. If no motor noise then thats an issue… All other indications are normal (light flashing, relay clicking).

If motor is moving and light is still flashing, then you just gotta drive around funny until it engages.

Here is the 100-Series wiring diagram:

Connectors BL1 & BF1 are the in-line harness connectors to the actuator, locations shown below. Splice point I16 is behind the glove box at the RDL relay.
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Thanks @Ayune
After replacing the wiring harness from BF1-BF2 to the locker actuator I couldn't hear the actuator make any noise. Thats why My fist thought was to check Voltage at the actuator connector and at BF1
Im getting 8.43V at BF1
If I understand correctly I should check also at BL1 and I16?
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Well if you’re not hearing the motor run AND the voltage is ~8.5V then the actuator motor is probably stalled, i.e. it’s being told to move by the ECU but it can’t because it’s at its travel limit. The motor is just a long winding of copper, or a big resistor that will drop voltage and get hot if it’s not moving, hence the ~8.5V you’re seeing.

The internal position switch (Motor pins 4, 5, & 6) report back to the ECU where the motor is, and if that switch isn’t talking correctly then the ECU will keep supplying 12V to the motor even if it can’t move anywhere, and you enter the 8.5V universe.

My suggestion is to measure how pins 4, 5, & 6 are connected when the RDL is disengaged (current state, right?): Unplug the actuator and check at the actuator that pins 4 & 6 are connected together, and pins 4 & 5 are not connected together. If those check out then we’ll move on to checking the harness or ECU. 🙂 ⚡
Does the actual diff lock ECU on the passenger side kick panel clicks?
I have always heard a click sitting on the drivers side towards the passenger side BUT yesterday with the ECU against my ear it did not click. The click is actually coming from the dashboard.
The ABS light comes on and the rear lock lights blinks as soon as the switch is activated thought.

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