Case of the Month: An Electrical Fire

Jan 2, 2014 by

The insured’s Mercedes-Benz C350 was involved in an accident.  The right front bumper, fender and door areas were damaged. A couple of months later,

 0114one

 

the Signal Activation Module (SAM) came loose on the vehicle and caused a short-circuit, starting a fire.  The insured said the accident caused the loose module and that the claim should be covered under the accident impact claim.  GEI was asked to inspect and photograph the insured’s vehicle to identify the cause and origin of the fire.  Could the accident impact have caused the module to become loose and resulted in the fire?  We also were asked to research any applicable recalls from the manufacturer.

First of all, what is a SAM?  This device functions much as a network router does on a computer or communications network.  It monitors input from various switches, lights, controls, monitoring devices, and warning systems.  There are SAM units at each large fuse panel including two under the hood and one in the rear of the vehicle. Typically, the SAM interacts directly with the ESP, SPS, BAS-controllers.  The rear unit also deals with all rear lights, closing the trunk, and fasten seat belts indications; additionally it reads the tank level sensor, a tilt sensor, door contacts, and the rear brake sensors.

Our inspection verified that the vehicle sustained damages from a right front impact, which were repaired to industry standards prior to our inspection.  No indications of fire activity were found to the exterior components nor to any components in the engine compartment.  No short-circuits or other electrical failures were found in the engine compartment.  The lines, hoses, and supporting components of the fuel injection, automatic transmission, power steering, and air conditioning systems were in place and intact.  The engine compartment fluids were found at their proper levels.

The interior of the vehicle was examined.  The stock stereo radio unit was found in place and properly mounted in the mid-dash area.  No indications of soot, melt damage, smoke, or other fire activity were located anywhere in the interior.

0114two

 

The trunk lid was opened to examine the reported fire area and the electrical components mounted in the trunk.  The battery, which was mounted under the trunk mat, and its terminals and cables were found in good condition in the floor of the trunk.

 

0114threev2

 

The SAM was removed from its mounted position and the SAM power supply cable was found loose.  The retaining nut for the top of the SAM had been previously removed and was lying on the carpet in the center of the trunk.  No indications of the retaining nut coming loose, such as wear or vibration marks, were located on the mounting ear of the SAM.  No rub marks were located on the inside of the trunk panel cover of the SAM.

 

0114three

 

No indications of fire or flame were found in the trunk or the SAM compartment that would indicate combustion had occurred.  No short-circuits or other electrical failures were found in the trunk or at the SAM.

The underside of the vehicle was examined.  The lines and hoses routed through the vehicle’s underbody displayed no indications of fire.  Old grease and dirt were found on the vehicle’s underbody components, and these highly flammable substances would have melted and/or burned during an active fire.  Further, a search of NHTSA recall campaigns for this year, make and model vehicle yielded a single possibly applicable recall (NHTSA PE13-026) related to rear lamp failures.  This could not have contributed to the problem.

The point of origin of the problem was located on the right side trunk wall.  The SAM plug had not been properly engaged in the SAM module; the loose connection created a high-resistance connection between the SAM and the power supply cable.  The power supply cable for the SAM was then lightly damaged due to this overheating.  The heat was sufficient to bubble and partially melt the power cable insulation.

 

0114five

0114six

Side and bottom views of the melted/bubbled SAM power plug

 Because the SAM is mounted vertically in the vehicle’s trunk, its power plug requires a vertical motion for removal.  The horizontal front impact that occurred two or more months prior to the date of loss would not have created the necessary vertical impact pulse to pull the module’s plug loose and would not have affected the integrity of the power cable.

Therefore the melted SAM plug was unrelated to the accident.

Related Posts

Tags

Share This