My 2000 ML had BAS, ESP and ABS lights on the dash and the scanner reported a wheel speed sensor issue (LR), which I replaced but the light would not disappear. Another scan said that there was an issue with the ABS pump (error code C1401). I spent ages search the Internet and I bought a workshop manual.
The issue is who to test if the pump is working. I put 12V onto the relay connector (#87), pump not responding, I took the big plug of the ABS module and checked if pin 15 and 8 have 12V and yes they did. Now all the recommendations regarding testing the pump itself was to remove the ABS unit completely, which I did, but turns out you can simply remove the pump from the rear, which is held by two T bolts. Once removed you can put 12V directly to the motor. My starting spinning right away and I think it was stuck, so this might happen again since the brushes might not be in great shape anymore. Anyhow after I pump the pump back in and started the car, all is GOOD!
