CODE 33: EXHAUST GAS SENSOR CIRCUIT (LEFT): a. Disconnect the battery. Place the terminals so that it cannot come into contact with the battery posts. b. Locate the O2 sensor on the driver’s side. It can be difficult to see with the brake booster in place, but it’s there. c. Follow the wires coming off the O2 sensor up to the connector. Remove the connector and clean the pins on both sides. d. Reassemble. Clear and run codes. If the problem persists, replace the O2 sensor (can easily be done by removing the brake booster)