Error Code P1135 is defined as Air/Fuel Ratio Sensor Heater Circuit Malfunction Bank 1 Sensor 1.

This error code is a manufacturer-specific trouble code, meaning it does not apply to all vehicles makes. Rather, it applies only to specific vehicle makes, such as Toyota, etc. Specification of the definition, troubleshooting, and repairs still vary from one make and model to another.


The A/F sensor or Air/Fuel ratio sensor has to reach a minimum operating temperature of around 1200˚ F to make an accurate voltage signal. The faster the air-fuel ratio sensor reaches this temperature, the faster it is for the sensor to start sending an accurate signal to the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes).

For the required temperature to be achieved, a heater element is included right inside the air-fuel ratio sensor. The PCM control this sensor heater element based on the signals sent by the engine coolant temperature and engine load.

The PCM controls the heater element circuit by allowing current flow to ground. The PCM monitors the voltage signal received through the heater element circuit. It determines the circuit’s situation by comparing the voltage detected with the factory specifications.

Error Code P1135 is set when the PCM detects a malfunction in the HO2S.

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system.

Possible Causes

  • Defective (A/F) Sensor Bank 1 Sensor 1
  • Open or shorted Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 harness
  • Poor electrical connection in Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 circuit
  • Defective PCM (rare)

How to Check

To check for this code, technicians look for the location of the Bank 1 Sensor 1 of Heated Oxygen Sensor circuit. Different Toyota models may have different positions for this code. An experienced technician can easily locate it.

The sensor must have a resistance specifications of:

68 F = 0.8-1.4 ohm

Above 68 F = 1.8-3.2 ohm

To check further, technicians will check for short or open in the harness of the Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1.

Next, they will check for poor electrical connections in Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1.

Exhaust leaks near the sensors must also be checked.

How to Fix

Common repairs for this code include:

  • Replacement of the Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1
  • Repair or replacement of open or short problem in the Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 harness
  • Repair or replacement of poor electrical connection in Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1
  • Fixing vacuum leaks

If the sensor is proven defective, then replacing it will fix the problem. However, it’s not always the sensor that goes bad. The sensor reads the mixture and efficiency of the vehicle’s combustion and triggers the error code if it determines rich/lean reading.

In some cases, Error Code P1135 is accompanied with Error Code P1155. If this is the case, then the fault must be caused by defective sensor fuse or relay. Start your diagnosis by checking the fuse. It must have 25amps.

After replacing the fuse and you still have the problem, then check for power at the sensor and the sensor relay (swap the relay to test).