My code reader tells me that the front wheel speed sensor is bad on my 05 chevy uplander. How hard is it to replace that can I do it myself or do i need to take it to the shop for that?

The code refers to the right front wheel speed sensor. The fact it is intermittent says that you have a bad connection or a fractured wire or a bad ground. Check out the videos

C0040 - OBD II Trouble Code: Right Front Wheel Speed ...

https://repairpal.com > obd-ii-code-c0040
C0040 18: Code C0040 18 indicates the ABS module has detected the right front wheel speed sensor signal amplitude is below minimum. More OBD-II Codes. C003E.

Video Help

if its circuit problem then will set off fault when turn key vehicle doesn't need to move

You will not notice any change in driveability due to ABS sensor. On braking the computer will not be able to control the anti lock system as it can not read the Left front wheel speed. Only time you will hear a woo woo sound if the Wheel bearing goes bad and has play. Otherwise if you plug in a OBD II code reader you will find
Code C0035 for Left front Wheel Sensor Malfunction.
Please read this article at Underhood service.com. link address is:
http://www.underhoodservice.com/wheel-speed-sensor-diagnostics-for-meters-and-scopes/

wheel speed sensor code. check the wires on both front wheel bearings. Most likely cause is a broken wire.

there is no c0400 there is a c0040 left front wheel speed check the wiring at the speed sensor about 3 to 6 inches from the conector on the body harness for a brake in the wirring

This is likely caused by a defective wheel speed sensor, there are 4 of them.

Assuming that you're talking about the front wheel speed sensors...
Your best bet is to replace both from wheel hub/bearing assemblies.

They'll cost about $100-$150 each.
When the wheel speed sensors are setting ABS codes it usually means that the bearings are bad.
When you replace the whole hub assembly, a new sensor is already installed in that hub. If it just the sensor (unlikely that just the front sensors alone are going bad) the sensor itself is usually 3/4 of the price of a new hub anyway.

I’m happy to help further over the phone at https://www.6ya.com/expert/jason_00b31cc8f593773a

Hello Abintz.
When your ABS light is on you have a problem in the system.
As long as the light is on your ABS system does not function at all.
If you have already checked the harness and connections the next thingt you can check yourself is resistance values at the wheel speed sensors.
One at each front wheel and one in the output shaft housing to the rear drive shaft.
They should read very close to 1000 ohms.
The front sensors are usually the area of most problems I see. They are replaceable.
Other than that you really would be hard pressed to find any other issues without getting it scanned by a repair shop.
If you have further questions please put them in "add comments and I will return to answer.
Best of the season to you.

KL

I do not beleive that there is a specific test for the speed sensors that measure the resistance of the sensor, if there is you should be able to measure the opposite wheels and figure out what it should be.

The best way to figure out what sensor is bad is to have it scanned, it may not be a sensor at all.

There are several TBS's and recalls on the wheel speed sensors, call a dealership and find out if yours qualifys.

Technical Service Bulletins
All Technical Service Bulletins:
Number Date Name
03-05-25-007C May 06 Brakes - Low Speed ABS Activation/No DTC's Set
04094 Jan 05 Recall - Front Wheel Speed Sensor Corrosion
05068C Mar 08 Recall - Possible Front Wheel Speed Sensor Corrosion
NHTSA05V379000 Aug 05 Recall 05V379000: Wheel Speed Sensor Cleaning