MACS Monthly Newsletter - 2020 - MAY8

Elmec

can both send commands (fan speed) and receive
messages (speed and status) over this single wire
bi-directional data bus going to and from the motors. LIN is not a bus that terminates at the DLC in
order for you to directly monitor with a scan tool or
scope. It does, however, communicate with another
module on the vehicle that serves as a gateway between LIN and a DLC bus such as CAN.
Diagnostics would include simply checking for
voltage drops / presence of power and grounds
and reviewing DTCs set in modules that interact
with LIN modules on the vehicle. When working
with LIN modules, keep in mind that any data you
might be reviewing about the module on your scan
tool is coming from another module on a data bus
that your scan tool can communicate with (such as
low-speed or high-speed CAN) via the DLC. Therefore, you're getting that information second handed
- it's what the other module is "telling you" about
another module on the LIN bus.

False Cooling Fan DTC:
2019 BMW X5, X7, 3 Series and Z4 Roadsters

Figure 11: Old-school techs can picture AWG - American
Wire Gauge sizes. Small sensor wires are around 20 gauge
while heavier wires for handling more current (such as cooling fan motors) are around 4 gauge. The metric cross-sectional area (mm2) for those same two AWG sizes would be
0.52 mm2 and 21.14 mm2 respectively.

BMW TSB SI B12 11 19 identifies an ECM software
problem which causes a false DTC 1A2014. Electric
fan function, switch-off due to under voltage. There
is no customer-facing symptom nor related check
control message displayed.
The TSB goes on to instruct techs to ignore the
DTC, clear it and program the ECM with updated
software to rectify the condition. As mentioned previously, the DTC in the ECM for the fan motor 's
incorrect voltage is the ECM's interpretation of
the LIN bus cooling fan module's supply voltage.
Thanks to a software glitch, that interpretation can
be false, thus the need for a TSB.
False interpretations can happen a lot when it
comes to things that are highly complicated. Hopefully this MACS Service Report has helped you to
more quickly and accurately interpret electrical
schematics. Until next time, stay healthy and thank
you for your essential services maintaining our nation's vehicles! n

can Wire Gauge) sizes as opposed to mm 2 (metric
cross-sectional area), a handy conversion chart can
go a long way (Figure 11) in helping to keep the
numbers more understandable. In the BMW schematic you'll notice a lot of circuits with 0.5 next
to the color designation and circuit number. The
equivalent AWG size would be around 20 gauge.
For the 800-watt fan, the power feed circuit is 16
mm 2 (5 gauge) while the 1,000-watt fan is 25 mm 2
(3 gauge).
One thing that keeps the BMW fan motor (and
grill louver motors) schematic (and system) simpler
(Figure 10) is the presence of LIN (Local Interconnect Network) data bus circuits. The DME (ECM)

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.

May 2020

MACS Service Reports

http://www.macsw.org

MACS Monthly Newsletter - 2020

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