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Disconnecting the onstar antennas will only affect onstar operation. It is safe to operate the vehicle with the onstar antennas disconnected. The P2135 code and reduced engine power message is due to a problem in the throttle position sensor at the throttle body. This is a common problem on these trucks. GM has issued a technical service bulletin to clean the throttle body and then replace the throttle position sensor cover on the throttle body with new design cover part number 19259452. This will eliminate the P2135 code.

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