Quick Tip Sunday (on a monday)

Chris Diagnostician New York Posted   Latest   Edited  
Tech Tip
Trained By Techs
2008 Lexus LX570 5.7L (3UR-FE) 6-spd (AB60F)
Center Diff Lock Light Blnking. Stuck In 4Wd Low

Last December I had a Lexus come in for window tint removal. We drove the truck to the tint removal place. They called us the next day, saying the truck was stuck in 4wd low and couldn't be driven. We had the vehicle towed back to us and I promptly put it in my bay. 

I started by verifying the concern. The center diff lock light was blinking and would not disengage 4wd low. I hooked up my scan tool and checked for codes, nothing. I hooked up Techstream, nothing. Come to find out, this module doesn't set codes. I then preformed a module reset ans wake-up, The center diff light went out! I tried to move the switch to 4wd high and I heard the motor work for a second and stop. The light Started blinking again.

I looked up the diagnostic procedure for the center diff lock. Like everything Toyota, it was lengthy and ridiculous. It involved digging out the 4wd control module, disconnecting it, and measuring the resistance of the pins for the position switches. This would've taken FOREVER. Plus, if it was an intermittent issue, an ohm meter wouldn't pick it up.

I needed a way to measure all the switch positions while manually activating the lock motor. The module shuts the whole system down when it detects a failure. I looked up a diagram. The motor drive and sensors are on one connector. I can cut the motor drive wires and manually hook them up while probing the sensor wires, and then repair when I'm done. 


I can use the AES Wave uTest Advanced Terminal Test Kit.

This kit is worth its weight in gold. From this kit I will be using the front probes, and this little guy right here

This nifty little do-dad allows me to create a custom break out box. I can connect the pins of of my choosing from the harness side of the connector to the component side of the connector and be able to monitor the signals. This allows me to "plug in" the sensors and leave out the motor drive. I used some spare front probes on the motor drive pins and hooked them up to a jump pack to move the motor back and forth.

When I actuated the motor. I heard a ratcheting noise, like gear teeth slipping. This vehicle uses plastic teeth to move the linkage back and forth (because Toyota). As the shift rod moves, the switches go high and tell the ecu what position they are in. You can see in the capture where the ratcheting happens. 

This vehicle needs a diff lock motor. I played with it a bunch of times and somehow found a happy spot that the vehicle and ecu liked. The light went out and the vehicle was able to be moved. We informed the customer of what is needed. They took it under advisement and took the vehicle. 

Could I have come to this diagnosis without this kit? Yes, but it would've taken longer and I would've had to cut and repair wires. The electrical part of this diagnosis took me about 20 min to set up. The OEM procedure would've taken over an hour, and still not have been definitive. This kit is probably the best 200.00 I've ever spent.

Here is the link to the pico capture if you want to play.

Thanks for reading.

Michael Diagnostician

Fantastic Chris and yes I agree resistance testing is not much use most times. I prefer to do what you have done here and measure while making it do its work so it is loaded in its normal habitat. I have seen so many fooled by resistance testing. Sometimes the best testing comes from creating your own and not following a flow chart

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Tim Curriculum Developer

Nice post! I agree that the uTest kit is a life saver. However, when using the kit to make other types of jumpers, the plastic around the banana connection is too thick to use with most test leads. I use this kit constantly, but I also have a handful of $3 adapters Like pt-TA016 from aeswave​.​com to make sure that every lead, jumper, device, adapter and gadget I own with a banana connection

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Chris Diagnostician
New York

I have a couple of those from a Matco kit. I love the AES kit. There is no part of it that doesn‘t get used.

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