On the 2004 Toyota Camry, the P2121 and P2128 are both pointing to a fault in the Accelerator Pedal Position (APP) Sensor. Carefully inspect the electrical connector and wire harness for any signs of loose, broken or damaged wire or any signs of water intrusion into the electrical connector. If the visual inspection checks ok, this is a fairly straight forward code and replacing the APP Sensor should solve the problem.
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