Audi A8 2019 Service Training page 39

ATF temperature regulation
The ATF temperature is regulated by a switchable coolant
circuit which runs parallel to the large coolant circulation
system of the engine. The circuit is opened or closed by
Transmission Fluid Cooling Valve N509 via signals from
Transmission Control Module J217 based on input from
Engine Control Module J623.
Engine warm-up phase (N509 closed)
Valve N509 is energized, and therefore closed, during the
engine warm-up phase. The ATF heat exchanger is not
flooded with coolant. Since the coolant does not release
any heat to the ATF, the engine reaches its operating tem-
perature more quickly.
The thermal management system of the ECM decides when
valve N509 is to be opened while Transmission Control
Module J217 sends the signal to actuate the valve.
The criteria for opening valve N509 are the ambient tem-
perature, the engine temperature, the ATF temperature,
the engine speed and the requested heat demand of the
climate control system.
ATF return line ATF supply line
2
ATF heat exchanger
Coolant supply
Transmission Fluid
Cooling Valve
N509
ATF return line
Note
If the ATF cooler is leaking, coolant (glycol) could mix with the ATF. Even the smallest quantities of coolant in the ATF can
have a detrimental effect on clutch control. A glycol test will detect even the smallest amounts of glycol. It can be used to
confirm or rule out this as a cause of transmission shifting issues.
Heating and cooling of the ATF (N509 open)
If the engine has reached its operating temperature and
there is sufficient heat for every requirement, valve N509
opens. The ATF heat exchanger is flooded with warm
coolant from the large engine coolant circuit. This warms
the ATF and reduces its viscosity, which in turn increases
the efficiency of the transmission.
The ATF is heated as long as the temperature of the engine
coolant exceeds that of the ATF. When the temperature of
the ATF exceeds the temperature of the engine coolant, the
ATF dissipates its heat to the coolant and is cooled.
N509 can be tested using the VAS Scan Tool.
N509
1
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2
ATF supply line ATF heat exchanger
Coolant return
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