Hey everyone. I was trying to help someone on here the other day with these codes so I thought I would just do some explaining so I could just link them to the topic which actually worked out pretty well since a vehicle came in and I was able to make a quick video on one of the issues that can cause this.
C0035 - Left front wheel speed sensor circuit.
C0040 - Right front wheel speed sensor circuit.
With these 2 codes you're more than likely going to find an open wire to the hub assembly speed sensor.
First before we get into testing at all just do a good visual inspection of the hub and harness. Some times the connector from the hub harness becomes disconnected from the retainer and the harness will rub on the axle causing wiring damage where the hub assembly has to be replaced. I have seen this several times.
But mostly what I find is the harness to the hub wheel speed harness is open requiring you to replace the harness.
The way you test this is by testing the resistance across the 2 terminals of the harness (the harness to car side, not the harness to hub side)
You will find the resistance is between 850 and 1350. While you have your meter connected, manipulate/wiggle the wiring harness and see if you can get it to show infinite resistance or OL. If it does replace the harness. You can use but splices, but I recommend soldering.
If the harness side doesn't show OL, Go to the hub harness connector and using the meter test across both terminals. Spin the wheel and with the meter on the mV AC voltage setting you should see at least 100 mV AC. If it is not greater than that replace the Hub.
Hope this helps someone and makes it a little easier to understand and diagnose. If you have any other questions you can leave them here or message me. I will be happy to try to help you.
Here is the video I made of replacing the harness.