MACS Service Reports - 2016 - JAN7

THE HEAT ISN'T ON, EVEN THOUGH THE PROBLEM IS "FIXED"

10), but unplugging its connector, which should get
it to open, doesn't seem to help. Could it be just
stuck in position? A lot of technicians would say,
"It's easy to change; I'll change it." But a new heater
coolant valve would be no help either.
At this point many technicians would be looking
at the electronic Automatic Temperature Control
system, with its IHKA (integrated heating cooling)
module and the sensors that feed it information.
Perhaps the IHKA module is sending a bad signal?
But the system works just fine in air conditioning
mode, so do you want to install an expensive module that might not fix the problem? Wait: there's a
temperature sensor in the floor duct. Could it be
faulty? Yes, it could. In fact, there's also a temperature sensor for the upper registers, in addition to
the in-car sensor. Do you want to throw another
part in and hope? There are no total-failure trouble
codes, and you can't easily test the sensors.
As you can see, the high tech BMW poses lots of
possibilities for diagnosis. In fact, the new models
also have a Climate Control trim adjustment in the
iDrive system, and a loss of performance could be
caused by someone unknowingly setting that.
One thing that we've learned over the years is
that some of the most sophisticated cars also suffer
some of the most basic problems. In this case there
actually was a hint in the failure of the auxiliary
electric water pump: the impeller had come apart,
breaking into small pieces and the engine water
pump sent them cascading through the cooling system. Actually, the pieces didn't travel very far; just
into the heater core.
The technician got to the point where he checked
the inlet and outlet temperatures of the heater,
and found a large temperature drop, indicating
a plugged heater core. The root cause may not be
the usual debris that we encounter, but when the
technician found that large temperature drop (yes,
something that should have been at the top of his
check list), he proceeded to forward flush and backflush the core. Little chunks of plastic from the impeller came out.
He may not have gotten out every last particle,
but when he put everything back together and carefully bled the system, it would peak at a floor outlet
air temperature of over 150°F. So the logic of starting with the most common possibilities and taking
it from there, only if necessary, gets another validation. ■

www.bmwtechinfo.com

Lack of heat on a BMW 3 series (2008 328i coupe)
had a number of possible causes, of course, but the
symptoms tended to push a technician in a few
directions. Fortunately, the radiator had been replaced (with an OE part) not long before, as a result
of accidental damage, so at least this was never even
put on the list of maybes. However, this car has an
auxiliary electric water pump, which should come
on with the temperature set to maximum heat, but
it didn't. Hot-wiring it also didn't do any good, so
the logical conclusion is that a new pump will take
care of this issue. The shop ordered one from the local dealer, installed it, and sure enough it started to
pump. With the heat set to max, the air temperature
from the center vents was a comfy 120°F, and even
at the outer vents was 100°F. However, the primary
issue is acceptable warmth from the floor outlets,
and here it was just 100°F. Tolerable perhaps, but
the weather hadn't really become frigid yet, and
any further drop would likely not please the customer. Further, as the interior warmed up a bit, the
air from the floor outlets started to drop; another
bad sign.
Naturally the technician had checked as best he
could to see that the HVAC flap doors both for mode
and temperature were moving normally. He had the
scan tool connected to verify coolant temperature
and it was around 200°F, which seems about right.
What now? The car has a heater coolant valve and
if it's stuck partly closed, that could account for the
poor heat. Not a difficult job to replace it (Figure

Figure 10: Heater coolant control valve on 2008 BMW 328i is a straightforward replacement. Unplug the connector (1), release the hose clamps (2),
disconnect the mounting (3), and you can take out the valve.

January 2016

MACS Service Reports

http://www.bmwtechinfo.com

Table of Contents for the Digital Edition of MACS Service Reports - 2016