Service 4WD message and C0035 and C0040?

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fishmaycraft

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We have a 2005 Yukon with the auto or manual push button 4x4 system.
My wife just informed me last night that the service 4wd warning light has been coming on randomly for the past few weeks. I took it to have the codes read and came up with both C0035 for the left front wheel speed sensor and C0040 for the right front wheel speed sensor.

Could this be what is causing the problem with the 4WD?

She didn't mention a braking issue but I'll drive it later to see if it is doing anything weird.

I should also inform you that last year we had an issue with the auto 4WD where it would engage in 4x4 when needed but not automatically disengage. To put it back in 2WD, you had to shift to neutral and push the 2WD button. A mechanic suggested it would be an expensive fix and since manual buttons still worked, we just went with that (only used 4x4 once or twice a year). There was no service message appearing then.

Thank you for your help!
 

tsuintx

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Since there are speed sensor codes, I would check at least the wiring and if that seems okay, then would change the sensors.

I would also consider changing the switch panel itself as that is known to cause the Service 4WD light to come on and some erratic behavior of the functions.
 

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