This is a real world diagnosis and repair of a 2000 Chev Suburban with a 4WD that will not shift back into 2WD, with a “service 4WD” message on the dash. Diagnostic code C-0305 was seen on a scan tool.
Note that in retrospect the sensor waveforms were not seen because there was an open on the sensor side of the breakout leads. For an updated accurate waveform see the followup video, https://youtu.be/_DPj8GbnrRg. Also note how the observation of a 0.7 volt bias voltage seen here but not seen in the followup video says something about the internal design of the circuit.
This is an amateur demonstration, offered in good faith for free, but with no guarantee as to safety or reliability of the information. Auto repair comes with intrinsic risks, risks that are clearly related the the experience of the technician. Any misadventure you encounter if you decide to accept the risk of fixing your own vehicle is your responsibility.
Music clip at the end is
Roboskater by Audionautix, licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/by/4.0/)
Artist: http://audionautix.com/
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At 8:36, the waveform shown is flat because there is a bad connection on the sensor side of the breakout lead. The module side of the breakout tap is intact, which is why we see the bias voltage. For anybody who is interested, I posted an video update today regarding the true waveforms, here https://youtu.be/_DPj8GbnrRg. The fact that bias voltage was present when the circuit was open suggests that the module uses that voltage to screen for circuit problems like open, short to ground, high resistance, etc. These two-wire variable reluctance analog sensors are very similar to old style wheel speed sensors.
Thank you for sharing this excellent video! I particularly appreciate your complete and thorough description of what you are doing. Good stuff!!
Been under my GMC SIERRA 4 days and tore
Dash a part. Check out
4 wheel panel. Automatic
4 lite up and 4 low lite up
In neutral 2 high. Check out
All ground's sanded put back got 2 high lite back
on tried reverse sounds like it 's ripping a part.
Banging .
Did you ever fix The transmission fluid leak? Or does anyone know where that might be coming from? Its a pretty heavy leak on an 03 avalanche and it seems like I would have to drop the trans to even figure out where it's coming from.
What kind of scan tool?
What kind of scan tool are you using?
Im gonna try this (sensors) maybe tomorrow. I've been told it probably the 2 solenoids on the side. This is easier and cheaper.
Thank you for this post . My 2000 Tahoe is doing this. It would shift in to 2 hi once in a while but now it don't shift in at all today . When I turn the key on it go s in to 4hi and won't unlock . The only way I could get 2 hi was to go to Auto 4wd and go back and forth a few times then all the lights go out and it goes to 2hi . So I need to change the front shaft speed censor ? And I can't get it in 4 lo at all either. The service 4 wd light stays on all the time too .
Another great video! Thank you for your time.
What happened to a dodge ??
Nicely done troubleshooting process. Thank you for taking your time to share valuable knowledge. God bless.
Remember the old days of getting out of the vehicle locking and unlocking hubs, no lights to deal with. Haha
Thanks for the video, very well done! Very nice equipment to have fun with also.
Stay safe and take care,
Bill
Fantastic editing with the picture in picture option. That helped move things along nicely. Too bad the expected wave pattern didn't take place. But yes, it's fun to use the tools you have…especially when you have time.
Nice job as usual. Very satisfying to keep older equipment running.
I enjoy the diagnostic testing and logical thinking to verify the problem, followed by schematics and diagrams to further be able to follow along. Thank you for taking us along the journey. Your friends and patriots from Fort Lauderdale Florida USA
A really good diagnostic video. Just wondering if the ABS light while on the stands could have been a slightly dragging disc brake or a bearing thats seen better days? Just a thought… Whats the hardware/software your using for a PC/Mac oscilloscope. We had to sell ours before we left on the big journey and I have to say we could have used it to help out a few folks, but space is an issue aboard. We have a boat a few berths away that has inverter issues on a pure sine wave inverter. I think the sine wave is clipped or modified not pure as its giving the microwave convolutions and has destroyed two toothbrush chargers. Thats almost always a sign (no pun intended) that the AC waveform is not right. So I want to check it….. Sail Safe guys. Ant, Cid and the pooch crew.
I have scan tool envy.
Many thanks for sharing – Although the diagnosis was interesting, the wrap-up at the end was a great instrument for approaching these things. Please keep them coming wherever possible. Thank you once again, from the UK.
370km on the original engine? If I recall you replaced the TC a few years ago, didn't you?
Nice to see you keep the old gal going. More money for new tools!
Don't worry about knotting my panties…I'm not wearing any! 😉
FIRST TIME VIEWER LOVE THE COMPLEX TROUBLESHOOTING POWERUSER VIDEOS… SO PLEASE KEEP THEM COMING THANKS FOR YOUR TIME !
Well done 😀
When you said there were two sensors i did wonder if they were kind and made them the same type, swapping was in my mind too :-D.
You have the dead one to hack apart if you are nosey like me ha ha 😀
I watch quite a few pro repairers and the pico pops up quite often.
South main auto and pine hollow diagnostics come to mind.
2 million ohms lol, as good as open circuit nearly.