MACS Service Reports - 2015 - APR1

Total Vehicle Climate and Thermal ManagementTM

April 2015

By Dave Hobbs, MACS Technical Correspondent
HITTING THE CURVE BALL: TEMP SENSOR STRATEGIES AND DIAGNOSTICS

General Motors

When you think of spring, you might think of
getting ready for A/C season, spring cleaning and
of course spring training it you're a fan of major
league baseball. Most batters like a straight pitch
right across the plate. Technicians must be like
baseball players too, because we hate it when technology throws us a curve ball! The examples of the
curve for this MSR come from Korea and Detroit.
I'm speaking of various temperature sensors and
their related circuitry within the modules that monitor them. Kia's quirky ECT strategy does throw us
quite a curve and OAT (Outside Air Temperature)
sensors have always been a bit confusing, so I'll
throw out some easy pitches on traditional temperature sensor technology first, and then get into the
tough stuff after that. Ever since electronics began
creeping into motor vehicles several decades ago,

Figure 1: Typical ECT disassembled showing the threaded shell (left),
thermistor element (center), and connector housing (right). If the
coolant is corrosive or the ECT is of poor quality, coolant can leak
through the shell and connector body seal on to the terminals. If not
repaired, the coolant can 'wick' it's way up the wire into the PCM
ruining it and the wiring it traveled through to get there!

A list of all thermistors used on automobiles would be
quite extensive. Here are just a few of the major hitters:

Dave Hobbs

ECT (Engine Coolant Temperature)
OTS (Oil Temperature Sensor)
IAT (Intake Air Temperature)
OAT (Outside Air Temperature)
DTS (HVAC Duct Temperature Sensor)
ETS (Evaporator Temperature Sensor)
Engine Oil Temperature Sensor (Diesel)
Fuel Temperature Sensor (Diesel, Flex Fuel and GDI)
12-Volt Battery Temperature Sensor
Hybrid Battery Pack Temperature Sensor

Figure 2: Typical NTC resistance vs. voltage relationship.

ALSO INSIDE THIS ISSUE:
ON BOARD DIAGNOSTICS .............................................................................................................................................................. 3
VOLTAGE DROP TESTING ON SENSOR CIRCUITS? YES! ...................................................................................................... 5
CRAZY KIA CASE STUDY .............................................................................................................................................................. 6

MACS Service Reports is the official technical publication of the
Mobile Air Conditioning Society Worldwide, Inc., P.O. Box 88,
Lansdale, PA 19446. The material published in MACS Service
Reports expresses the views of the contributors and not necessarily that of MACS. Every attempt has been made to ensure

April 2015

the accuracy of the content of MACS Service Reports. MACS,
however, will not be responsible for the accuracy of the information published nor will MACS Worldwide be liable in any way for
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MACS Service Reports

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