Jim Grant's Tech Tips
96 Ford Aerostar, Check Engine Light On
a 96 Ford Aerostar with v6, 3.0L. The check engine
light is on and the code is P1443 which is related to the
evaporator pressure sensor. I replaced the sensor, checked
the valve and it is Ok, replaced the canister and a few
hoses. The check light still comes ON even after it was
cleared. Any suggestion on how to fix this problem?
your situation I would suggest not using the OBD II type
codes if they were obtained via generic OBD II data acquisition.
First you have to understand a little bit of how the computer
tests these parts . The code you’re reporting can be set
by a functional failure or by a circuit failure. Either
the component being tested did not work as designed or the
electrical part (wire or the wire in the component) has
a problem. When you start and drive your vehicle the computer
performs a function test of the canister purge solenoid.
During the function test the computer uses the voltage signal
from another sensor to see a change. When the computer commands
open and closed some other sensor reports that yeah I saw
a change. Thats the function. Then while you’re driving,
the computer keeps an eye on the circuit (the wires to and
from). This is called the circuit test and this test happens
all the time. Heres where those high end or factory computer
scan tools really shine. The scan tool can command the computer
to perform a function test right in the shop with key on
and the engine off. This allows the technician to check
the operation of the parts without the hazard of hanging
off the side of the vehicle with test equipment at 40 MPH.
(Which is a good thing.) You’re at the point where what
is needed is information, real diagnostic equipment and
a well trained technician. Anyone can be shown how to get
a code from a vehicle’s computer. To get it fixed right?
You know the answer.