MACS Service Reports - 2016 - FEB3

near zero (under 0.1 volt). If it is above 0.1, there's a short to voltage in the wire to #
41. Not a particularly likely occurrence, but it does occur. If the voltage reading drops
to near zero, turn off the ignition. Reattach the connector to the sensor.
3. Next (ignition off), connect a fused jumper wire from the PCM's 5-volt reference
terminal (# 54) to the refrigerant pressure sensor signal terminal, at the sensor
terminal # 3 if you're using a voltmeter, to the PCM # 41 if you're using a scan tool
plugged into the OBD-II connector. Turn on the ignition and the voltage reading
should be in the range of refrigerant pressure (under 4.9 volts, usually close to 1 v
per 100 psi). If it's 5.0 v and above, there's a short to ground in the 5.0 v reference
line. If the voltage reading on the pressure signal line is under 4.9 volts, turn off the
ignition, remove the jumper wire and proceed to the next step.
4. Turn on the ignition and check voltage from terminals 1 to 2 of the sensor and
it should be above 5.0 volts. If it's lower, turn off the ignition and check the low
reference terminal by connecting with an ohmmeter for a poor ground (over 5
ohms). If the resistance is high, unplug the connector at the PCM and check the low
reference line for high resistance, perhaps even an open.

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The diagnostic sequence that GM recommends really isn't a lot different, and in the
case of P0530, it's really not particularly tedious. Naturally it uses the scan tool to
check out the refrigerant pressure sensor, but you also can use a voltmeter if your
scan tool doesn't display the necessary PIDs (data items). Here's a summarized
version of basically what it is (refer to wiring diagram, Figure 3):
1. Make a voltage check at the PCM's refrigerant pressure signal terminal (# 41 on
the 4.2-liter six) and if you get an acceptable reading when you turn on the ignition,
the sensor and its circuit are okay. That reading should be in the range of 0.1 to 4.9
volts (actually it will be somewhat higher than the minimum if there is normal refrigerant pressure in the system). If you get a good reading, any problem is elsewhere in
the system or is an intermittent. GM has a comprehensive procedure for checking
for intermittents, in fact to induce them. But in this case a wiggle test done comprehensively is an alternative. We cover the GM procedure later in this report, but let's
continue with P0530 and the GM test sequence.
2. If you don't get the acceptable voltage reading at # 41, turn off the ignition, unplug
the connector at the sensor and turn on the ignition. The voltage reading on the connector wire terminal # 3 from refrigerant pressure signal terminal # 41 should be

Figure 3: Wiring schematic for 2004 Trailblazer manual A/C compressor control circuit. Note low pressure switch at right end of diagram, wired to HVAC control
module. But P0530 diagnostic is done at PCM and A/C refrigerant pressure sensor. Diagram lists PCM terminal numbers for both 4.2 inline six and 5.3 V8.

then as he's wiggling the harness up to the pressure sensor, the
A/C cuts out (Figure 2). This confirmed that there apparently is
a break in the harness. There are two ways to find the break: 1)
Peel back the harness covering from the sensor until the technician comes to an identifiable break in one of the wires. 2) Turn
on the ignition and measure the reference voltage (should be
almost 5 volts) at the # 2 terminal of the sensor (from the powertrain computer terminal # 54 with the 4.2-liter six). And then
see if there's continuity in the other two wires from the sensor to
the PCM.

February 2016

Another trouble code (actually three codes) that raise(s)
questions
Sometimes a failure will raise several trouble codes, even
though only one of them really applies. This happens because of the way the diagnostic software is written and the
trouble codes are displayed. Example: trouble codes are
logged for high voltage, short, open and low voltage. Surely
the system failure can't be caused by all of these, and the
truth is that it was not. The software just automatically took
any failure in

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