MACS Monthly Newsletter - 2017 - AUG8

WIRING ISN'T ALWAYS WELL-PROTECTED

acdelcotds.com

The P0530 trouble code is one of the most common on
General Motors vehicles when there's an A/C failure. It's the
A/C pressure sensor, or is it? The description actually calls it
"Air Conditioning Refrigerant Pressure Sensor Circuit," but
many technicians who log the code will just start by installing a new sensor. And in almost all cases, the problem will
remain. The more diligent technicians will observe that the
description includes the word "circuit," and they'll check the
sensor connector, and if that's good, they'll often stop there
and look at the wiring diagram. In this case it's a 2006 Chevy
Silverado 4.8-liter V8 (Figure 14).
Well the harness soon disappears from the sensor area,
and it's a matter of "where do we go from here?" There's
a lengthy test sequence for the P0530, but too many technicians look at the many steps and decide that the last couple
of steps are to replace the Powertrain Control Module and
reprogram it. If they decide to do that, they'll also usually be
disappointed.
Okay, what's the alternative? It comes down to "biting

the bullet," by following the diagnostic steps, and here we'll
warn you, they may not end well, as you'll see. If you look
at the wiring diagram, the refrigerant pressure sensor is
less than a couple of inches from the PCM. But in the real
world, the sensor is in the high-pressure line at the back of
the compressor. The PCM is at the left front of the engine
compartment, just to the left of the fan assembly. The route
the harness takes is another matter, running underneath the
front underbody, where it isn't surprising that wiring damage could occur. And we know from the symptoms that we
have an intermittent wiring issue. But let's start with the factory diagnosis anyway.
The first step is to connect a scan tool, and with the engine
off, turn on the ignition, note that it has an A/C pressure sensor parameter on the data list, with the reading anywhere
from 0.1 to 4.9 volts. If the reading is within that range,
you're referred to diagnostic aids, which consists of testing
for intermittent wiring connections.
In this case the harness takes a circuitous route close to and
following the transmission oil
cooler lines, and where they
take a 90° bend, the technician
peeled back the conduit at the
bend and found damaged
wiring, which he repaired to
fix the problem. What tipped
him off? It was that he would
get occasional, instant readings on his scan tool, which
indicated an intermittent
somewhere in that harness.
Wiggling the harness in the
right place will usually get
you to the location, but most
harnesses do not follow an
open path for an easy wiggle
test, and some intermittents
respond only to heat or cold.
So yes, when an intermittent
is indicated, you'll often have
to go through removal of panels, covers and components
that restrict access. Hey, no
one ever said this was an easy
Figure 14: The P0530 trouble code diagnosis starts at the refrigerant pressure sensor connector (bottom of diagram business. ■
of a 2006 Chevy Silverado with 4.8-liter V8). But there's actually a long harness between the pressure sensor and
the Powertrain Control Module and a wiring problem in that harness was not easy to trace.
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 Forcey
Manager of Service Training:
Steve Schaeber
Mobile Air Conditioning Society Worldwide
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017
Email: membership@macsw.org * Website: www.macsw.org

Unless otherwise noted, all photos/art by author.

August 2017

MACS Service Reports

http://www.acdelcotds.com http://www.macsw.org

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