MACS Monthly Newsletter - 2021 - MAY5

Figure 8: Normal vs. VCI: 99% of the time when you program a GM vehicle's module you will select " Normal " (as opposed to
VCI) in one of the steps leading up to actually selecting and downloading the actual calibration. VCI (Vehicle Configuration
Index) is a special calibration that GM's Techline engineering group gives to GM dealer technicians for special situations
where there is a missing calibration, a special calibration for a specific problem or a change of various options that effect
the accuracy of a calibration (i.e., a tire size or axle ratio change). Whether independent repair shops who purchase programming subscriptions from GM (via ACDelco) can obtain / purchase a VCI number from GM remains a mystery to this
author at the moment. A VIN, TSB number and a phone call to the GM dealer which you have a good repour AND parts
purchasing history with, would be my recommendation if you ever need to attempt to obtain a VCI number.
for programming the compressor control module. I was looking at what
looked like an official GM TSB, and there was not a single mention of programming the module. The only repair mentioned was performing a battery power reset to the vehicle!

VCI numbers (last I heard) were privy only to GM dealerships, although
at one time you could call the hotline associated with your GM TIS subscription and request a VCI number in instances where the factory choice
was not applicable (i.e., tire and axle ratio changes). One would assume
that the TIS2Web hotline folks would gladly issue a VCI number in the case
of the Volt TSB? Word on the street is that GM is no longer granting VCI
numbers to the aftermarket repair shops, so a trusted and helpful dealership contact may be your only recourse.

Have I been working too hard? Am I losing my ability to comprehend
technical documents? Surely not? I then turned to ALLDATA and found the
TSB. All 8 steps (including step 7 for programming the compressor control
module) were in the ALLDATA version of this TSB (as I had recalled), so I
breathed a sigh of relief (I'm not losing it quite yet)! Now I'm curious as to
why NHTSA showed a 7 step TSB while ALLDATA showed 8 steps (which
included the reprogramming step). My next method to find out the truth
was to go to the manufacturer's official website - GM's SI2000. Even though
it cost $20 for a 3-day subscription, I had to verify the official procedure.
Sure enough, GM's factory service manual showed the same version of the
8-step process (including step 7 for reprogramming the A/C compressor
control module) just like I found in ALLDATA. The reason for the omission
of the programming step in this TSB on NHTSA's website (and the reason
for the TSB being totally absent on Mitchell), still remains a mystery. However, one thing was confirmed once again: you can never have TOO many
sources for service information! v

The Mystery of GM TSB #18-NA-096
You may have noticed that Step 7 of GM's TSB #18-NA-096 was underlined and in bold in this report. The emphasis is purely my doing. In my
research for this MSR, I discovered that Shop Key Pro (Mitchell) did NOT
have ANY trace of that particular TSB! Since I had the TSB's number, the
next thing I did was Google it on the web. NHTSA (National Highway Traffic
Safety Administration) was listed near the top of my Google search for TSB
#18-NA-096, so I opened it up to grab a few more details prior to writing this
report. That's when I discovered the absence of ANY mention of a programming procedure in the NHTSA's version of TSB #18-NA-096.
I initially jumped to the conclusion that I somehow imagined the step

Toyota Compressor B1479 Case Study
/ compressor speed sensor connector, there is a 2-wire connector to the
compressor's PWM controlled variable displacement solenoid. The 3rd
connector gets even more confusing. This connector is a 3-wire connector
to a Hall Effect sensor for refrigerant flow. Using traditional 5-volt reference,
reference low (sensor ground) and a 0 to 5-volt analog sensor output, the
sensor tells the A/C amplifier if there is refrigerant flow. No flow is closer to
5-volts. Good flow will read out a lower voltage.

Some Toyota / Lexus A/C compressors might be considered a bit more
complicated than many others on the market. Their wiring schematic circuit labeling further complicates the matter (Figure 9).
In addition to the traditional 12-volt power feed to a traditional magnetic
clutch, the same connector contains an RPM signal (and sensor ground)
that tells the A/C amplifier (control module) the speed of the compressor. The A/C amplifier may call out this RPM signal as " Lock " (Figure 10),
if there is too great of a difference between engine speed and the compressor speed signal (Figure 11). In this case, the A/C amplifier considers
the compressor locked up. The A/C amplifier then signals the ECM to have
the bussed electrical center (engine compartment) to switch off the power
feed (via a solid-state relay) to the clutch, in order to prevent the serpentine drive belt from being thrown off. In addition to the clutch coil power

May 2021

This leads me to a TSB which for some reason, only applies to 2012-2013
Toyota Camrys. Toyota TSB # T-SB-0084-13 advises that there may be a DTC
B1479 set in the A/C system either as a current or history DTC due to a
malfunctioning A/C compressor flow sensor. The TSB advises technicians
to check the voltage of the A/C compressor flow sensor for being under 3.7
volts with the engine running and the A/C off. It should be over that value if

MACS Service Reports

MACS Monthly Newsletter - 2021

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