MACS Service Reports - 2016 - MAY7

EVEN THE LOWER PRICED CARS
- nothing wrong with that, but it turns out the body computer
has to be programmed according to the transmission, in this
case a four-speed automatic. Although you might think that the
transmission programming has nothing to do with the HVAC,
there is a specific A/C programming command that has to be
selected. Another basic car, another A/C programming requirement.
There are more and more of these jobs coming into aftermarket shops, so you have to face reality. And it shouldn't be hard.
Starting with GM cars is an approach that many shops have
taken to programming computers, for these reasons: 1) all the
software is available on short-term availability at gmtechinfo.
com for two-day "rentals." 2) the single-make "Mongoose" tools
($495) are a low-cost price of entry into J2534 programming and
diagnostics for GM. You naturally will also need a Windows PC
and good internet connection.
MACS had a course on programming at the training event
in Orlando in February, 2015, and although other classes were
well-attended, this one could have handled a lot more people.
Those who did come saw how straightforward the process is.
With the online tutorials and hot line help from companies that
sell the J2534 tools, including Mongoose supplier Drew Technologies (www.drewtech.com), you can successfully start too.
Other suppliers of J2534 programming devices include: Bosch
Diagnostics, Snap-On, Blue Streak Electronics (bsecorp.com), and
Delphi (co-op with Blue Streak).
Hopefully this article is a convincer for a lot of MACS members who still think they can "wait it out." Yes, there's a learning
curve, but it isn't rocket science and it won't clean out your bank
account. ■

We've heard the line often enough: "I work mainly on the
mainstream cars. If something complex comes in on a high-end
model I send it to the dealer, pocket my discount, the customer
gets a fixed car and I don't invest in all the expensive equipment."
We've often talked about reprogramming, and this time when
we say it, we'll include a pretty mainstream example, in fact on
one of the lowest-priced cars on the market, a 2010 Chevy Cobalt with that 2.2-liter pushrod engine and basically a manual
HVAC. The A/C, the recirc and the rear defrost buttons do not
function (not even the heat). The technician connects his premium aftermarket scan tool (you do at least have one of those).
This car well precedes the General Motors models with the new
Global Diagnostic System.
The scan tool did not even see a response when A/C was requested. The shop first suspected the control panel, and with a
duplicate Cobalt model available, it tried the control panel from
that, and there was no difference. That threw the suspicion on
the body computer (BCM if you prefer), which (as you probably
thought from the start) is where it belonged. So the shop got a
new body computer and installed it. End of story? No, because
that BCM has to be programmed, and although the technician
in this case was able to do that and send the car on its way, you
would have to reprogram it too - or send it to the dealer.
Once more, and this car is even less expensive than the Cobalt:
a 2008 Nissan Versa, which has been the industry's low-price
leader for years. In this case the technician had already replaced
the body computer and the control head panel for an A/C problem. The A/C switch works and the compressor engages - but
as soon as the blower switch is turned on, the compressor shuts
down. If you don't do programming, you'll be checking the
compressor circuit for a short, then checking power and ground

SECOND TIME'S THE CHARM
We've all heard this line, "I've checked everything, and it's
all good." Maybe it's from one of your technicians, or a call
from a friend with a shop across town, or even you. The
problem often seems so simple you can't believe the technician is still struggling with it. When the answer comes up,
no one can believe it. "I'm sure we checked that" is an oftenheard comment.
Example from 2006 Jeep Liberty with the 3.7-liter V6: no
A/C because the compressor clutch isn't engaging - this
should be easy. The technician connects his scan tool and
can engage the clutch that way, which seems to say that the
clutch circuit is intact. So he tries once more to do it by pressing the A/C button, but all that happens is that the fan starts
spinning. Well at least he knows that the fan circuit isn't involved.
The wiring diagram for the clutch circuit (not shown)
doesn't show much - just the relay circuit, and he realizes
there has to be more involved in clutch control. But he
knows, and we hope you've also learned, that you usually
have to look at a number of diagrams, and not all of them
are labeled HVAC. So he wanders around the wiring dia-

May 2016

grams and finds one for the blower motor, and he notes that
includes the A/C-low pressure switch (Figure 11), which if
you know this vehicle, is plainly located on the accumulator
(Figure 12). It doesn't control the clutch directly, but is the
key input to the powertrain computer. He jumpers across
the switch and tries the A/C once more, but still no clutch
engagement. So now he does a point-to-point wiring to
relay check. Starting with the fuse for the Auto Shutdown
Relay and finds nothing amiss. Yes, if he grounds the relay
coil terminal with a jumper, the clutch will engage before he
starts to think about being cursed, he realizes the powertrain
computer isn't providing the relay ground.
At this point, some technicians would replace the powertrain computer, but this technician did the right thing:
he continued to wander through the wiring diagrams and
found one for the body computer, which showed a high-side
transducer, which is used on many Chrysler products. Of
course, routine underhood inspection would have shown
it too. Everyone knows that transducer is a pattern failure,
although it's wired to the body computer, which talks to the
powertrain control module. So without going further, the

MACS Service Reports

http://www.drewtech.com http://www.bsecorp.com

Table of Contents for the Digital Edition of MACS Service Reports - 2016