P0135 = upstream O2 sensor heater not working. Cold O2 sensors take too long to reach operating temp, causing running in open loop longer. Fix: 1) Check fuse for O2 sensor heater circuit. 2) Test sensor resistance at heater terminals — should be 5-20 ohms. 3) Check wiring for breaks. 4) Replace O2 sensor if heater element burned out internally. Upstream sensors (before cat) more critical than downstream. Denso and Bosch are quality choices.
P0135 O2 Sensor Heater Circuit Bank 1 Sensor 1
Check engine light. Fuel economy slightly worse. Sometimes rough idle on cold start. This fault code is stored when the engine control unit detects a specific fault condition. Common causes include sensor failures, wiring faults, and component wear. Always read additional fault codes before replacing parts — multiple codes together provide a clearer diagnosis. Clear the code after repair and test drive to confirm the fault does not return.
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No commonly reported misdiagnoses for this fault yet. If you have replaced a part that did not fix this problem, submit a wrong diagnosis report — it helps other drivers avoid the same costly mistake.
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