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P1135 - Faulty AFR Sensor and How to Fix It

AFR sensor

One of the more common error codes (OBD II codes) to set off the repair/engine light on a Toyota vehicle is P1135. User matvey in our forums had this issue with his Camry. Code P1135 is "Air/Fuel Ratio Sensor Heater Circuit Malfunction Bank 1, Sensor 1."

This is the first "oxygen" sensor on the manifold. This is not, hwoever, a standard O2 sensor as found on many vehicles, but is instead an AFR or A/F sensor (air-fuel ratio sensor). These are a bit more complex than the standard O2 sensor is.

An A/F sensor reads the oxygen and returns those readings to the engine's computer (engine control module, or ECM). The A/F sensor is more precise than a standard O2 sensor and must be operating at a specific temperature (1200F) to accurately get a reading. When something goes wrong with the heating element that keeps the A/F sensor at that temperature, code P1135 results.

There are three main reasons this code could be tripped, outside of the ECM being faulty. Either the sensor itself is faulty, the wiring to it is faulty, or the circuit is broken. Because of this, simply changing out the (rather expensive) sensor is not always the immediate solution.

A circuit test of the Bank 1 sensor should be done first, looking for poor connections, shorts, or outright breaks in the circuit. This can be achieved by tracing the wires from one point to another, testing that section, then moving on to the next, the next, and so on. This will usually begin at the sensor, run back to the harness, then through to the various relays until reaching the ECM.

If no faults are found, replacement of the sensor is the next step.

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