MACS Service Reports - 2015 - JUN2

not. The better scan tools often are able to go well beyond "basic," in which case you'd see the sensor reads significantly lower
than shop temperature.
The car manufacturers have recognized that this is a problem
and in some cases there is a manual reset to update the vehicle's
ambient temperature sensor. On most Ford products, just press
the A/C and Recirculation buttons simultaneously, then immediately press A/C again (Figure 2). If there is no manual reset,
there may be a software update that speeds up the temperature
update. The issue of outside air temperature sensors is one that
the car makers recognize as a problem area, and you can be sure
they're paying close attention to it. Some cars have a "virtual"
outside air sensor, that is, they use the engine inlet air temperature sensor in conjunction with the coolant temperature sensor.

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The inlet air usually is picked up from a cool air source, and that
can distort the reading if the algorithm isn't robust.
Of course, some systems just have a default setting instead of
a sensor. That is, there's just a number in the software, say 72°F,
and use the in-car sensor and the driver's setting of the A/C control as the primary inputs for A/C operation. So if you do get a
reading on your scan tool that seems far off, it may not be a defective sensor; rather, it could be an anomaly in the software or
excess tolerance in those sensors that produce the virtual reading. Look at the coolant and engine air intake sensors if that occurs. They may be well out of spec when compared with readings from good shop thermometers.
We'll put an emphasis on "good," because shop thermometers
are not necessarily as good as you'd like. An infra-red type can't
read air temperature. Other shop thermometers we've had are
often all over the place. So we keep recommending that you
handle them carefully (including putting them, not tossing
them, into a toolbox), and periodically checking them to see
if any one differs markedly from the others. It's either the one
that's right or the one that's very wrong. You've got to find out
which. At least once every couple of months, check in boiling
water (it's always 212°F). We don't guarantee that a boiling water reading of 212°F means the thermometer also is accurate at
an air temperature of 75°F, but the only positive way to get a
reading that starts low and goes through the range is one with
a thin wire probe you can slip between a coolant hose and neck
as close to the coolant temperature sensor as possible, and compare the readings on the electronic thermometer versus the scan
tool display of the coolant sensor. If they differ by more than a
few degrees, it may be the tipoff that you need to check further.
Yes, you also can use an infra-red thermometer on the coolant
temperature sensor, and if you use it carefully, you should get
readings that are reasonably close and rise at about the same rate
as the engine warms up. ■

Figure 2: Ford's outside air temperature reset for most late models consists of
pressing the recirculation button (3) and the A/C button (5) simultaneously,
then the A/C button immediately following. Other controls shown are (1) temperature, (2) mode, (4) rear defog and (6) blower speed.

WHEN A CONNECTOR IS MORE THAN A CONNECTOR
You see the plastic electrical connector and maybe it looks
bad; perhaps cracked, maybe it has a partly melted look, or
is singed. That's got to be the cause of the circuit problem,
right? Good chance, although that singed look likely was
caused by a wiring issue that you first have to identify.
But there's more to the picture, because in a lot of shops,
looking to get the job out the door that day, there's the temptation to make a jury-rig fix, by cutting off the wiring before
the connector and using terminals from a universal kit to
make individual connections.
As we said, that singed look likely has a cause, so even
if the connections are carefully made, we don't necessarily
have a fix.
Here's an example from a 2007 Toyota Avalon. Turning
on the system doesn't produce immediate results of any
kind until the defrost light, which starts blinking immediately, stops. At that point the HVAC display comes alive and
blower speed and temperature control both work, as does
the dashboard display. The problem is loss of mode control,

June 2015

with just a little airflow from the vents. There are two sunload sensor codes, but most technicians by now have learned
that the sunload sensor, although given an increasing role in
the control strategy in recent years, still primarily performs
a trim function. The technician did confirm that the sunload
sensors would respond to application of light, so he could
exclude them from further diagnosis.
The third code, B1443, was somewhat obvious; it's for the
mode control servo circuit. That's certainly the problem area,
but what to do now? He cleared the codes, but they came
back immediately.
The motors are wired in series and are in buss-type circuits, so the motors can be reversed. The technician naturally
checked for power and ground and found he had both going
into the actuator housing (listed as the A/C-blower assembly in the diagram). He removed the connector and applied
power and ground directly, finding he could control the
mode servo. So although an aftermarket diagnostic routine
he found said he should replace the A/C amplifier,

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Table of Contents for the Digital Edition of MACS Service Reports - 2015