Brake Failure

Case Description:

An ARCCA expert was asked to investigate a case where a driver claimed that his anti-lock brake system (ABS) failed, causing him to lose control of his vehicle during a heavy rain storm. The driver had taken his vehicle to the dealership for service numerous times due to an intermittent ABS light coming on indicating a possible ABS system failure. During these visits the light was ‘off’, and the technician claimed a failure could not be determined. A few days after the last visit, the driver had an accident during the previously mentioned heavy rain storm, causing damage to the vehicle and injury to the driver.

Steps Taken:

ARCCA’s expert reviewed the recalls and technical service bulletins (TSBs) for the vehicle and found a TSB for an issue with the wiring in the wheel speed sensors. During his inspection, he found a bare wire on the left front wheel speed sensor that could cause an intermittent short, just as described in the TSB. This intermittent short would cause a failure of the ABS system. While the driver could still brake, without the ABS function there would have been diminished stability control due to the wet road conditions.
The expert used a scan tool to look into the history section of the diagnostic trouble codes (DTCs) to see if this defect caused a DTC to be set in the past. It revealed that an ABS fault code for the left front wheel speed sensor had occurred numerous times.
The expert also imaged the ACM that did have a non-deployment event recorded. There was no indication of an ABS failure or brake failure in the crash data retrieval (CDR) report. However, there was an indication of hydroplaning in the report that would indicate a stability problem occurred, as claimed by the driver.

Final Findings:

ARCCA's accident reconstruction expert concluded that the bare wire on the front left wheel speed sensor, as described in the TSB, caused failure of the ABS system thus resulting in diminished stability control under wet road conditions. In this case, if the CDR report was the only information gathered from the inspection and a further review of the recalls, TSBs and brake system inspection were not performed, it is possible this failure would have been overlooked and the claim deemed to be unfounded or from human error. Researching the background and completing a full mechanical inspection helped ARCCA uncover the cause of the incident after a lack of data from the CDR report.