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Rough Idle for GMC

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KEYWORDS GMC Mitchell 1
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 Create an 8-inch ground wire using ring terminals and 14-gauge wire.

Owners of a 2020-2021 GMC Sierra 2500/3500 equipped with a 6.6L engine may experience a rough idle and reduced engine power. The SES light may be on, with DTC P0123 and P0222 active or in history. This condition may be more noticeable in very cold climates.  The condition may be caused by an internal circuit board fault within the throttle body.

Replace the throttle body. Using two 8mm ring terminals and one 8-inch 14-gauge wire, make a good ground wire. Remove the oil fill cap and beauty cover from the left bank rocker cover. Attach one end of the new ground wire to the lower right throttle body fasteners with the crimp side of the ring terminal facing towards the bolt head. Attach the other end of the ground wire to the rocker cover fastener with the crimp side of the ring terminal facing towards he bolt head. Road test to verify the repair.

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Attach the other end of the ground wire to the rocker cover fastener.


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