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Errorcode C1025 / BAS ASR lamp stays on while motor is running

Posted on 29. September 2016 in Cars Mercedes Benz C-Klasse TC 220 CDI BJ1999 / W202

Hi all,
recently the BAS and ASR lamp of my motorcar stayed on while the motor was running. The cruise control is also not working.

Tools used:

 

Reading out the errorcode came to the result:

BAS reported the errorcode C1025
which could mean
* CAN communication with ABS (N47) not working
* CAN communication general fault
* signal from break light switch fault
* CAN signal wheel speed sensor or ABS fault

1.) check the signal integrity of the CAN C BUS

CAN C – Engine CAN or chassis CAN, fast speeds 125kbps or 500kbps
CANH active 3,5V, dormant 2,5V (Usupply /2 = 5 / 2 = 2,5V)
CANL active 1,5V, dormant 2,5V

001_can_motorraum

 

 

 

 

 

2.) check the signal integrity of the CAN B BUS

CAN B – Interior CAN or body CAN, low speed 83kbps
CANH active 4V, dormant 1,6V (Usupply /3 = 5 / 3 = 1,6V)
CANL active 1V, dormant 3,3V (Usupply * 2/3 = 5 *2/ 3 = 3,3V)
003_gesamter_bus

 

 

 

 

 

3.) Check the wheel speed sensors

Find the ABS control unit in the electrical box at the front right side of your motor room.
Unplug the whole connector and measure the DC resistance.
Lift up a wheel and spin it, the result should be a sine wave.

ABS / connector #2 / PIN 43 + 44 / Resistance 1,1kOhm
Front Left :
vl

 

 

 

 

 

ABS / connector #2 / PIN 17 + 18 / Resistance 1,1kOhm
Front Right:
vr

 

 

 

 

 

ABS / connector #1 / PIN 12 + 13 / Resistance 1,1kOhm
Left Rear:
hm

 

 

 

 

 

ABS / connector #1 / PIN 14 + 15 / Resistance 1,1kOhm
Right Rear:

<no picture available>

The sine wave of the Left Rear sensor does not look clean. Unscrew the sensor, clean the impulse ring, replug. Check the signal again, bad luck, no change. Buy a replacement part, Error is gone.