GMC 2010 Sierra - Manual (Page 451)

3. After the electrical connection is made to a trailer
equipped with electric brakes:
. A TRAILER CONNECTED message will be
briefly displayed on the DIC display.
. The Trailer Brake Display Page will appear on
the DIC showing TRAILER GAIN and TRAILER
OUTPUT.
. In the Trailer Output display on the
DIC, “- - - - - -“ will disappear if there is no error
present. Connecting a trailer without electric
brakes will not clear the six dashed lines.
4. Adjust the Trailer Gain by using the gain
adjustment (+ / -) buttons on the Trailer Brake
Control Panel.
5. Drive the vehicle with the trailer attached on a
level road surface representative of the towing
condition and free of traffic at about 20 to 25 mph
(32 to 40 km/h) and fully apply the Manual Trailer
Brake Apply lever.
Adjusting trailer gain at speeds lower than 20 to
25 mph (32 to 40 km/h) may result in an incorrect
gain setting.
6. Adjust the Trailer Gain to just below the point of
trailer wheel lock-up, indicated by trailer wheel
squeal or tire smoke when a trailer wheel locks.
Trailer wheel lock-up may not occur if towing a
heavily loaded trailer. In this case, adjust the
Trailer Gain to the highest allowable setting for the
towing condition.
7. Re-adjust Trailer Gain any time vehicle loading,
trailer loading or road surface conditions change or
if trailer wheel lock-up is noticed at any time while
towing.
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