Electronic Throttle Bodies or throttle by wire systems have no accelerator cable and are responding to commands from the powertrain control module. Contained in the throttle body are two position sensors that relay the throttle position information back to the powertrain module so that it can "see" the response of the throttle to its commanded actions. Absolute Throttle Position is the data item for the primary sensor monitoring the butterfly valve angle. Absolute Throttle Position B is from a secondary sensor reporting the same information but on a different circuit to the powertrain module. This redundancy is for safety purposes and allows the powertrain module to cross-check and verify the information. Notice in the wiring diagram that the two sensors do share the same reference and return circuits.
If the computer notices a discrepancy in the two signals it will set a fault code and go into a failsafe or limp-in mode that doesn't allow but a minimum of throttle. P2135 would be a result of that discrepancy. You can monitor and compare the two sensor outputs by looking at Absolute Throttle Position and Absolute Throttle Position B. They should correlate closely as the throttle moves.
On this particular application the signals are a mirror image of each other.
Thanks for reading!
Kenny@GGAuto.Repair
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