Thanks. What's the difference between a drain and a flush?
A flush is done by adding fluid at at the coolant return line and letting the fluid run out from the coolant send line. It is not recommended by GM anymore.
Bulletin No.: 04-06-01-029J
Date: March, 2020
INFORMATION
Subject: Unscheduled Supplemental Services (Including Flushing Services and Additives) and
Models: 2020 and Prior GM Passenger Cars and Trucks
This bulletin has been revised to add the 2019-2020 Model Years, update the Attention
statement, remove the Approved Transmission Flushing Tool (Transmission Cooler Only)
section and add Canadian information in the first bullet under Our Commitment to providing
Quality Service to Our Customers. Please discard Corporate Bulletins 04-06-01-029I and
12-06-01-008B.
Subsystem Flushing
Flushing of air conditioning (A/C) lines, radiators,
transmission coolers, and power steering systems are
recognized practices to be performed after catastrophic
failures or extreme corrosion when encountered in
radiators. For acceptable A/C flushing concerns, refer
to the Flushing procedure in Service Information (SI).
This practice is not required or recommended for
normal service operations.
The use of external transmission fluid exchange or
flush machines is not recommended for the automatic
or manual transmission. Use of external machines to
replace the fluid may affect the operation or durability of
the transmission. Transmission fluid should only be
replaced by draining and refilling following procedures
in Service Information (SI). Refer to Automatic/Manual
Transmission Fluid and Filter Replacement