MACS Service Reports - 2015 - APR8

MACS Service Reports is published monthly by the Mobile Air
Conditioning Society Worldwide. It is distributed to members
of MACS Worldwide and is intended for the educational use of
members of the automotive air conditioning service and repair
industry. Suggestions for articles will be considered for publication,
however, MACS Worldwide reserves the right to choose and edit
all submissions.

Editors:
Elvis Hoffpauir, Steve Schaeber
Production Designer:
Laina Casey
Manager of Service Training: Steve Schaeber

Unless otherwise noted, all photos/art by author.

Email: membership@macsw.org * Website: www.macsw.org

April 2015

Mobile Air Conditioning Society Worldwide
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017

MACS Service Reports

Delphi

the microprocessor to handle the increased tranIf you haven't asked "what fixed the van" yet,
sistor control. The engine experts at Delphi worked you are a very patient reader! It seems that this rare
and conspired with their software gurus to come up but normal condition of a pulsing ECT was happenwith an innovative strategy to turn two transistors ing way too much, so there had to be something
on with one logic output (Figure 15). That, in and more wrong with the vehicle other than an OEM
of itself doesn't seem like such a great feat, until anomaly. After all, the customer was still complainyou consider that both of those transistors won't ing about the MIL. A voltage drop test on the ECT
necessarily need to turn on at the same time. Think revealed a problem. A couple of new terminals on
about it: The engine coolant and transmission flu- the ECT connector, DTCs cleared and an extended
id are often pretty close to each other temperature road test took care of the customer problem. Almost
wise. There are times, however, when the transmission as important, after a lot of head scratching, a little
fluid gets warmer than the coolant and vice versa. Un- education courtesy of Kia's OEM service training
like the GM two step resistor strategy that only has to website took care of the technician's problem. After
worry about the ECT, this PCM has to tailor its internal all, some of us in this business need to know the
pull up resistor(s) to not one moving target but two. En- details of 'why' almost as much as we need to know
gineers came up with the idea that whenever the differ- the practicality of 'how'. ■
ence in temperatures between the ECT and OTS were
greater than 30°C (54°F), the logic control
circuit wired in parallel to both of the PCM's
two step pull up resistor transistors would be
turned on. A reading would be taking by the
PCM on the thermistor that needed the extra resistor pulled out. The transistor would
then be turned off to allow the PCM to take
a reading off of the other thermistor that still
needed both of the pull up resistors internal
to the PCM (Figure 16). The switching of both
transistors on and both transistors off occurs
at such a fast rate you would swear the PCM
is going crazy, hence the two PCM replacements that didn't fix anything. The service
Figure 16: There is a "TR" (transistor) for each of the two paired thermistors (coolant
engineers at KIA immediately put this inforand transmission oil) but only one logic circuit to control them. Under conditions when
mation in their training materials, which, by
both fluids are close to the same temperatures, the single control circuit is off and both
the way is available with your service inforthermistors use the full internal pull down resistance with the PCM. When one of the
mation subscription to the Kia OEM service
thermistors moves more than 30°C (54°F) from the other's value, both transistors are
triggered ON by the PCM.
manual on-line.

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