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Jim Grant's Tech Tips
'94
Mercury Villager, Crazy Brakes and Power Lines
Q:
When I'm driving my
“94 Mercury Villager van under high power lines, the brakes buck,
the pedal pushes upward and won't stop till I put the car in park and
remove my foot from the brake. The car bucks forward and it's dangerous.
It's getting more and more sensitive and is doing it for lesser power
lines. What the heck is that?
A:
You’re not alone
with this problem. We’ve had two other vehicles of your type in the
shop with the same complaint. It was hard at first determining the cause
for the problem until one customer said it happens at the same place every
time, which happened to be under a set of power lines. Her husband confirmed
our suspicion by driving the vehicle under the same power line and applying
the brakes. The anti-lock brake system would just flip out, with the ABS
computer was thinking it was in the panic stop of a lifetime. The ABS
computer would not calm down until the vehicle was brought to a stop after
the power lines. Once the cause for the ABS system flip-out was determined,
his wife did not want anything to do with that vehicle and traded it in.
At this time we only have a theory that the grounds for the wheel speed
sensor shields were/are bad. The wiring for the wheel speed sensors travels
the length of the vehicle; they could be acting as a receiver. Power lines
have a very strong magnetic field. When another wire comes under the influence
of a magnetic field it will produce electricity, this electrical theory
is call mutual induction. If our theory on the ABS problem is correct,
then the power lines could create a signal/voltage in the ABS wiring that
would cause the ABS computer to believe that there is an ABS event occurring
of a grand scale. Our theory was applied to the second vehicle and all
the grounds for the ABS shielding were cleaned and serviced. We have not
see or heard back from this customer, so we have no idea if this was an
effective repair.
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