CITROEN C5 MK2 ABS LIGHT ON

[crosser69]

Recently changed the o/s rear trailing arm on my C5 mk2 estate,i had to put a 2nd hand one on as the arm had worn oval,the 2nd hand one came with the caliper and disc fitted so i fitted the whole lot.had to drill the old abs sensor out of the 2nd hand arm,put car back together and now the abs and esp light comes on,how do you check a abs sensor? Or does the arm i bought(off a 2003 car) have a different abs set up on it?
Any help would be appreciated,i dont mind driving around in it as i know all the brakes are spot on,ive tried disconnecting the battery but the same happens once i start the car.

[Lighty]

Start by checking the ohms resistance of the Abs sensor and compare it with the other side.If you disconnect the battery and the light comes straight on, then a sensor must be faulty.
If the sensor was ok, but not picking up the signal, the light would stay off until you moved the car.

[crosser69]

i disconnected the battery,then started the car,abs light came on after 5 seconds,i then drove it down the road and it went off and then came back on 5 seconds later along with the anti skid light..how do you check the ohms?