MACS Monthly Newsletter - 2020 - APR1

Total Vehicle Climate and Thermal ManagementTM

April 2020

By Dave Hobbs, MACS Technical Correspondent

Equinox Cooling System Case Study
looked fine, Mike wasn't taking chances, so he replaced the ECT pigtail harness with a new one. The
P0128 continued to set so Mike posted a request for
help. He starts out with the vehicle service history
and then added an observation, that following a
cold start and 10 minutes at idle, the scan tool reads
150°F on the ECT sensor PID.
Twenty minutes of driving moved the temp PID
to 195°F, and another twenty minutes or so to get
to the 220°F mark where the cooling fan kicked in.

Replaced thermostat for P0128 - MIL Still Coming On

Gates

Recently I ran across a case study / request for
help posted online by one of my friends (let's call
him Mike), a very conscientious and experienced
master technician. He uses OEM parts whenever
possible, does extra research when diagnosing and
always gets the car fixed right the first time. Mike
had been working on a 2012 Chevy Equinox with
a 2.4 Ecotec engine. The vehicle had over 250,000
miles on it when Mike replaced the radiator and
heater core before they failed from the extreme
miles. He had also replaced the water pump just
prior to the heater core and radiator due to a slow
leak at the pump's vent hole. Mike also replaced the
thermostat, heater hoses and radiator cap, something any tech should do on a high mileage vehicle when performing other cooling system repairs.
After the repairs were complete, the SUV ran great
with no coolant leaks, no overheating and a properly performing heater.
Two weeks later the MIL came on.
A P0128 will set if the cooling system temperature rises too slowly or there is a fault detected in
the cooling system. Considering the description of
the DTC, Mike's experience told him that he could
have received a faulty thermostat from the dealer,
so he returned it for another OEM stat. The same
DTC returned. From there Mike wondered if the
ECT (engine coolant temperature) sensor could be
skewed enough to cause the DTC so he replaced it.
The P0128 persisted.
We've all seen ECTs leak and cause electrical issues at the actual connector as well as a few inches
beyond that as the coolant wicks its way up the
wires. Even though the connector on the Equinox

Figure 1: This thermostat (#33568) incorporates a jiggle
valve (brass pin on top of flange) to allow for air in the system to bleed off by passing it into the radiator. If the stat
doesn't have one there is most likely an air bleed notch on
the flange to accomplish the same goal. This same stat is a
bypass design. Note the bottom spring on the stat.

ALSO INSIDE THIS ISSUE:
The Quest for Quality Auto Parts ..................................................................................................................................... 8

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 2020

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 injury, labor, parts or other expenses resulting
from the use of information appearing in MACS Service Reports.

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