ACTION NAPA AUTO CARE - 7

Engine cooling systems: Electric cooling fan operating strategies

When things go wrong...

Troubleshooting electric fans
Traditional fan diagnosis usually begins with the basics, including
a visual inspection of the fan itself, wiring and harness connectors,
fuses and relays. If you ﬁnd a problem that's a common ﬁx, such as
a replacing a blown fuse or relay due to burned contacts, be sure to
double check the repair. We all know that sometimes they just blow,
but taking the extra step to verify current draw with an amp clamp
only takes a few minutes, and may prevent a comeback if the system
fails again.
If all that checks out, scan tool diagnosis is a logical next step.
With today's fan systems being controlled by the PCM, using a scan
tool to command fan operation really makes for a quick way to narrow down the list of fault possibilities. Even though there may not be
a diagnostic trouble code to coincide with an inoperable fan, a quick

MACS

Richard McCuistian

Electric cooling fans are generally reliable, but sometimes may
fail to activate due to an inoperative or defective thermostatic switch,
sensor or relay. This may cause the engine to overheat. Diagnosing
a failure of this type can sometimes be time consuming, and also require special electronic diagnostic tools.
Since the majority of fan systems and radiators are relatively exposed within the engine compartment, they are particularly prone to
failure or faults caused by dirt or debris from the road. Frontal impact can also result in damage to the radiator and fan. Furthermore,
as components age they become increasingly susceptible to cracks
and corrosion in vulnerable areas such as mounting points and welds.
When a failure occurs, it can have a direct impact on the operation of
the engine and air-conditioning system, with serious consequences
in terms of both safety and comfort. Damage to the radiator can have
a knock-on effect on other components in the cooling and air-conditioning systems. The cumulative damage can be extremely expensive,
particularly in the event of complete engine failure.
Dirt and debris play a bigger role than you may think. A local shop
told us about a temporary repair they made to a slow-turning radiator
fan. Parts were not available at the time, and the customer was "in a
pinch." So the shop removed the fan assembly from the vehicle and

current ﬂow, oxidation, resistance, heat, and the melting of things that
comes with that syndrome. And sometimes, those failures can spill
over to cause problems in other systems.

This fuse melted on a 2004 Chrysler Sebring (it
didn't blow, it just melted), taking the engine cooling fan ofﬂine. Fortunately, we were able to clean
the connector in the junction box well enough that
all we needed to do was replace the fuse. We coated
the terminals with dielectric grease to prevent future
oxidation.

separated the fan from the motor. The technician blew the motor off
with shop air, during which time clouds of dirt came billowing out of
the vents. Turning the motor shaft by hand, the technician noticed the
bearings felt dry and there was a bit too much end play. Nevertheless,
they cleaned and lubricated the parts, reassembled, and were able to
get the customer rolling until replacement parts arrived a few days
later.
Cooling fans operate in a most hostile environment, and the circuits that make them work are also subject to the "snowball effect" of

Check to see if you can command on either one or both
fans with a scan tool. In many cases, these bi-directional
tests can be found in your tool's menu.

check of some key data points may help you out. When checking
out the data stream PIDs, pay particular attention to those related to
engine cooling that may initiate fan operation. You'll want to check
PIDs such as ECT Sensor, A/C Pressure, Engine Load, Ambient
Temp, and those for the Cooling Fan Relay(s), which will usually
display as ON or OFF.
If you're working on an older system where the PCM does
not control the fan, it's a process of elimination, but be sure
to follow the correct wiring diagram. Some techs like to start
at the power side, and work their way through the system to
ground. Others start at ground and work towards power. Either way, you're doing the same thing: trying to locate a broken wire, bad connection or some other fault preventing the
fans from running. ❆

Spring 2015 * ACTION/NAPA

ACTION NAPA AUTO CARE

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