have a 2010 Toyota RAV4 that had the same tire pressure light
problem noted in your recent column. Took the car to the dealer as I
was mystified — all four tires were within 1 to 2 pounds of each
other in pressure. Final solution — the spare tire was low on air.
received a number of similar responses to the question regarding the
low tire warning light on the 2005 RAV4 — thank all of you for
taking the time to share your experiences.
In the case of
the 2005 RAV4, however, the spare tire cannot be the culprit for the
simple reason that the spare does not have a tire pressure sensor
installed. In fact, none of the tires have an internal pressure
As I described
in my original answer, this vehicle has an indirect tire pressure
sensing system that does not rely on individual tire pressure
sensors. Rather, it utilizes ABS wheel speed sensors to recognize
differences in rotational speed of the wheels while the vehicle is
in motion. Assuming all four tires are the same make, size and
circumference, significantly low tire pressure could cause a tire to
have an effectively shorter radius — distance between wheel
centerline to pavement surface — and thus rotate at a different
speed. At a certain threshold of differential speed and resonance,
the low tire warning light will be triggered.
Q: I have a
2000 Ford Explorer that for the past two years won’t start in cold
weather. I tap on the fuel tank and it starts. A shop checked all
sensors and does not think it is a fuel pump problem because it
happens so seldom. Besides, it’s a $600 repair. Any suggestions?
A: Have the
shop monitor the amperage "draw" of the fuel pump. The
fuel pump of the 4-liter engine delivers 55-65 psi fuel pressure
with the key on and the engine not running. As a general rule,
electric fuel pumps draw roughly one ampere of current per 10 psi of
fuel pressure, so the pump for this engine should draw roughly 7
amps. Significantly higher current draw is indicative of high
electrical resistance in the circuit or pump. As does that
"tap" on the bottom of the fuel pump to vibrate the pump
enough to get it started — another clear sign of a failing fuel
Q: I have a
2001 Dodge Dakota with V-8 engine, 4WD and automatic transmission.
When driving down the highway, occasionally the engine RPM will
shoot up, then drop back down. There is no slip in the transmission
or loss of speed. Would this be a sensor or module for the
transmission? Or is the transmission getting ready to quit?
A: If there
actually is no sudden slippage or change of gear in the
transmission, the issue is likely with the instrument cluster and/or
tachometer. But if you hear the engine actually rise in RPM, the
transmission must be downshifting, unlocking the torque converter or
the brake pedal slightly and/or manually downshifting from overdrive
back to drive — do either of these actions replicate what you’re
experiencing? If so, the powertrain control model, or PCM, may be
sensing a need for more power and commanding these actions. A scan
tool may be helpful in identifying any issues with the transmission
or its control module.
Q: I bought a
2005 GMC Canyon in 2006 with 31,000 miles on it. The Hankook tires
on it when I bought it still look new and I can’t see any
checking. I have driven only 6,000 more miles it since I bought it.
Do you think I can still put more miles on them without problems?
A: In my
opinion, yes. While tires do deteriorate over time, it sounds like
the tires on your vehicle are still entirely serviceable. To make
sure, have them inspected by a tire shop annually. Unless there’s
an identifiable problem, they should remain serviceable at least 10
years with your low annual mileage.