Diagnose and fix Toyota P0136 or P0138
Trouble codes P0136 or P013 are a fairly common problem on Toyota. Toyota has issued a service bulletin T-SB-0001-10 to address the P0138, P0158 or P0606 issue. The bulletin applies to the vehicles listed below.
NOTE: These vehicles use two different types of sensors; air/fuel ratio and O2 sensor. Everyone calls them both oxygen sensors but they ARE DIFFERENT. An air/fuel ration sensor is installed upstream from the catalytic converter and is used to control air/fuel mixtures. The O2 sensor is installed post catalytic converter and is used just to confirm that the catalytic converter is working properly.
What the Toyota P0136 or P0138 trouble codes mean
P0138 Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)
CAUSES: Open in HO2 sensor (sensor 2) circuit, bad HO2 sensor (sensor 2), bad HO2 sensor heater (sensor 2), problem with Integration relay (EFI MAIN relay), Gas leakage from exhaust system
P0136 Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
CAUSES: Open or short in HO2 sensor (sensor 2) circuit, bad HO2 sensor (sensor 2), bad HO2 sensor heater (sensor 2), bad Air-Fuel Ratio (A/F) sensor (sensor 1), problem with Integration relay (EFI MAIN relay), Gas leakage from exhaust system
Diagnose Toyota P0136 or P0138
In order for the post cat sensor to read high voltage there must be a rich mixture coming out of the cat or the sensor itself is faulty. Start by checking the response from the post cat sensor by purposely introducing a large vacuum leak. That should force the post cat sensor to read lean. Then force a rich condition. If the post cat sensor responds properly, then the air fuel ratio sensor isn’t properly controlling air/fuel mixtures, which would force a steady rich or lean condition in the post cat sensor. Test the air fuel ratio sensor by checking the voltage readings. The air fuel ratio sensor should read between 3.35 and 3.70 volts and the post cat sensor should read 0.70 to 0.90 volts. If the air fuel ratio sensor readings are off, replace the sensor.
If the post cat sensor doesn’t respond to the vacuum leak and rich condition, replace it.
In most cases, shops discover that the problem is a faulty air fuel ratio sensor, NOT a bad post cat O2 sensor. Automatically replacing the post cat O2 sensor simply because it is listed in the trouble code is a common DIY mistake. DON’T BE LIKE EVERYONE ELSE. Do the testing
Vehicles affected by Toyota service bulletin T-SB-0001-10
2005 – 2010 Avalon
2007 – 2009 Camry
2009 – 2010 Highlander
2007 – 2010 Sienna
2009 – 2010 Venza
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