Case study: ABS fault
Figure 1: The battery bus bar connection to the main electrical feeds was heavily corroded
By Des Davies, Top Gear Motor Services Vehicle: VW Golf mk4 2.0 2000 Mileage: 98,710 A customer brought the Golf into the workshop as the ABS light was illuminated on the dash, as well as a ‘STOP’ and brake fault indicator lights. No previous work had been undertaken apart from a recent battery replacement and the vehicle had not been driven much due to Covid 19 restrictions. My first task was to confirm the faults with the ignition switch on, then conduct a quick visual check of the ABS system to check for anything missing, loose or damaged – it all looked good.
CASE STUDY
I then scanned the whole system looking for faults, to gather live data and have a direction to work on. The fault codes generated were:
10
ABS fault codes 01276, ABS Hydraulic Pump (V64): Signal Outside Specifications & 00668, Supply Voltage Terminal 30: Signal Outside Specifications I had seen code 00668 come up on a few occasions with some other systems, so I decided to check the battery voltage and condition. As you can see in Figure 1, the battery bus bar connection to the main electrical feeds was heavily corroded
and when the voltmeter was connected to the terminal and along the bus bar the voltage readings were fluctuating between millivolts and around 6-8V. Could this be my problem? A nice easy fix… no such luck! I removed the terminals and bus bar, cleaned, replaced and retested and had 12.4V on my multimeter. I cleared all the codes only for all the lights on the dash to reappear, followed by the codes. I checked all the fuses to the ABS and electrical circuits that were on top of the battery – there were three ABS fuses and five battery supply fuses. On testing these, I had 12.4V either side of the fuses, indicating good supply voltage. I needed a wiring diagram of the ABS circuit to check the power and grounds to the ABS ECU, see Figure 2. Due to
