Ford speed control deactivation switch fires

Nov 1, 2008 by

As the family stumbled out of bed, no one doubted that there was a fire. A quick call to 911 brought the fire engines to the house. They evacuated the residents and knocked down the fire in about a half hour. The house was pretty much a total loss. Their two vehicles, which were safely locked in the garage, were also completely destroyed by the fire. A couple days later, the fire department investigators followed up, and determined the fire had started in the garage. GEI was brought in at that point to find out what really happened.

The two vehicles that were consumed by the fire were a very nice, late model expensive European sedan and a late model Ford pickup truck. Our expert followed the evidence trail and agreed with the fire department that the fire did, indeed, start in the garage. Furthermore, he pinpointed the cause down to a specific part under the hood of the pickup truck.

The specific part that was the culprit was the Speed Control Deactivation Switch (SCDS). This kind of switch was installed in over 16 million Ford/Lincoln/Mercury vehicles from 1992 through 2004. The National Highway Traffic Safety Administration and Ford Motor Company have since recalled 10.3 million of these vehicles to date. These include cars, trucks, and SUV’s that have this switch as part of their cruise control system. But, interestingly, 5.7 million other Ford vehicles, with this specific switch, have yet to be added to the recall lists.

When the driver activates the cruise control and later steps on the brake pedal, the cruise control is electrically turned off (deactivated) by the same electrical switch that turns on the brake lights at the tail of the car. This switch is mounted on the brake pedal lever or arm, under the dashboard of the car. But what would happen if that small switch failed? The driver would then have to manually deactivate the cruise control-not a good plan, especially in an emergency situation.

Ford, therefore, came up with a better idea. The SCDS is a redundant (back-up) system that also deactivates the cruise control when the brakes are applied. The SCDS is located on the end of the brake master cylinder, usually pointing to the front of the vehicle, and sometimes pointing down to the ground. When the driver applies pressure to the brake pedal, a small sensor in the hydraulic brake system translates that increase in hydraulic pressure into mechanical movement. That mechanical movement pushes two electrical contacts away from each other to break open a previously closed electrical circuit. This turns off the cruise control. In this way, if there is a failure in the brake light switch, the SCDS takes over for the primary electrical deactivation switch located under the dashboard.

The SCDS is a 4th generation, $20.57 pressure switch built by Texas Instruments to Ford’s specifications. Texas Instruments states the switch was designed to handle a small (1-2 amperes) intermittent DC load. But Ford installed the switch into a 15 ampere circuit.Instead of an intermittent application, the circuit is energized at all times, even when the vehicle is turned off and the key is out of the ignition. This is why these vehicles can catch on fire in the middle of the night, while parked in a garage, and having been unused and unattended for many hours. As originally installed, the power to this switch is never turned off.

The SCDS fails when brake fluid from the hydraulic side of the switch leaks through a barrier membrane, into the electrical side of the switch. Brake fluid is hygroscopic, meaning it readily absorbs water from the air, which then coats anything the brake fluid touches with water also. This results in corrosion and a conductive path-to-ground short-circuit. This short-circuit leads to overheating and melting of the wiring and copper contacts, setting fire to the plastic enclosure, and resulting in a fire that can consume the vehicle.Some SCDS fires are relatively small with only minor damage. Others become a runaway freight train that consumes the entire vehicle and anything within twenty feet. Each fire is different because conditions are different.

When the expert goes through the progression of steps to investigate and eliminate all possible points of origin and causes of the fire, he also locates the evidence needed to support his conclusions. With SCDS fires, the switch may still be attached to the brake master cylinder or it may have fallen onto the frame rail or the ground below the vehicle, depending on the severity of the fire. The recovery of the SCDS component is important in supporting the expert’s opinion of the origin and cause of the fire.

Other factors that may be reported by the owner, in addition to the burnt SCDS itself, may show that a failure was beginning to occur within the SCDS. If the vehicle’s cruise control was not operating properly (unwanted disengagement), if a mechanic mentioned to the owner that the vehicle had evidence of brake fluid leaking from the switch, if the vehicle had trouble shifting out of PARK, or if the fuse for the cruise control was melted, then the additional symptoms of a short-circuit and failure within the SCDS become additionalevidence for the expert to consider in his analysis.

To further demonstrate the short-circuit within the switch, an analysis by a laboratory can be performed to verify the failure. The copper contacts and electrical terminals of the switch are encased in plastic and sit atop a part of the switch called the Hexport. The Hexport is screwed into the end of the brake master cylinder. If the plastic pieces are still attached to the Hexport (however burned and melted the plastic may be) they can be non-destructively x-rayed to show the failure. If the switch failed, the x-ray will show the melted copper within the burnt plastic casing. If the internal parts are intact and not melted, then the switch did not fail. If the burnt plastic casing and contacts are not recovered, the Hexport itself can be examined by a Scanning Electron Microscope with Energy Dispersive X-Ray Spectroscopy (SEM/EDS), looking for evidence of melted copper on the Hexport. If fragments of copper are found melted onto the Hexport, this confirms that a short-circuit occurred within the switch. If there was no short-circuit, no copper is fused onto the Hexport and the SEM results will not report copper deposits.

A fire that started in another part of the vehicle (fuel system, electrical system, power steering, or air conditioning), or a fire started outside of the vehicle, does not burn hot enough to melt the copper. Only a short-circuit within the switch itself is able to generate the temperatures required to melt the copper parts, leaving their traces on the face of the Hexport. Thus, thorough laboratory testing can verify the failure of the SCDS. These SCDS fires have caused extensive property damage and even resulted in loss of life. Until the recalls are performed on all of the 10.3 million vehicles, these fires will continue to occur. And remember, 5.7 million vehicles with the same switch have yet to be added to the recall list. As the switches continue to age, more seals will fail.

If you have a Ford vehicle fire, or a structure fire that included a Ford, it would be wise to see if a failed SCDS may be the culprit.