MACS Service Reports - 2015 - APR7

kiatechinfo.com

General Motors / Dave Hobbs

Figure 14: The Delphi PCM in this Kia Sedona looks like any other PCM
on the surface. If you only watched scan tool PIDs, and never monitored
sensor values with a meter or scope, you would never pick up on the very
unique ECT / OTS strategy used.

Figure 13: When the ECT voltage dips below 1 volt (122°F or 50°C), the
ECM / PCM turns on a transistor which changes the effective value of
the pull down resistor internally. This gives better resolution when the
engine begins to warm up for more accurate fuel control. GM and others
have been using the stepped ECT strategy for many years.

tool? Why wouldn't you simply just watch a scan
tool's PID for ECT while the engine warms up? Remember fail-soft? Scan tools can lie / be told to lie,
and since this Kia minivan has been into the shop
numerous times for the same problem with a great
deal of expense, it would make sense to use alternative test methods. If you are not a scope user, you
can watch a meter for several minutes (DC volts),
back probing the ECT while the engine warms up
/ cooling fan cycles. Place the meter in min/max
mode to catch any quick glitches. If you are using a
scope, you can set the scope's time base up to capture several minutes of warm up / thermostat cycle
time.

Conquering the Kia

April 2015

Delphi

In the case study on the Kia, when a lab scope was
back probed into the ECT circuits under the hood
to monitor voltage (temperature) at the sensor as
the engine ran, an unusual pattern was observed
when the engine began to get warm up. The voltage
seemed to go 'haywire,' rapidly fluctuating from
high to low. The scope was actually able to capture
a square wave at the ECT when the time base was
sped up to measure a faster event. The techs were
puzzled to say the least. Apparently the engineers
in Kia's training department were also puzzled by
this observation when the vehicle was first built,
so they asked their PCM supplier (Delphi) for an
explanation (Figure 14). It seems that Kia's requirements for a fast, accurate and powerful PCM were
not exactly conducive to also provide the same
PCM in the small and inexpensive package that Kia
required. The vehicle utilized multiple engine man-

Figure 15: The 5 volt reference for each sensor comes in at the top of each
transistor (gate) and travels through R1 and R2 (totaling about 4 kΩ)
when there is no base current applied to the side of the transistors by the
single common circuit called "Pull-Up Control". One circuit controlling
both transistors means both thermistors turn on / off at the same time.

agement thermistors, each needing a two step pull
up resistor (remember GM's strategy?) applied. The
ECT required a superior sensor resolution strategy,
as did the transmission's OTS (Oil Temperature
Sensor). There were not enough logic outputs on

7

MACS Service Reports



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

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