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Answered 2010-11-24 14:45:08

P1155: Air/Fuel Ratio Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

The sensor is on the Bank 1 throttle body with electrical connection. Its a delicate sensor. Unscrew it from the throttle body and check if its dirty, spray it with electronic cleaner with care. If its damaged, just replace it.

If its not rectified, the car computer may default the air temperature to 20 degC and the air flow will not be correct and may have the following effect:

1. You might have difficulty in winter startups 2. Loss fuel efficiency (air/fuel ratio is messed up)/NOx problems/failed emission test/prematured catalytic converter replacement etc.

CLARIFICATIONAn Air Fuel Ratio Sensor is also known as Wide Range Oxygen Sensor.

Bank 1 Sensor 1 is mounted in the exhaust header before the Catalytic Converter (CC). The ECU uses the signal from the AF sensor to adjust Air/Fuel ratio. On V6 and V8 engines there is a second AF Sensor in the other header. (Bank 2 Sensor 1).

After the CC there is a narrow range O2 sensor called Bank 1 Sensor 2. It monitors the CC. If there are two CCs there is a second O2 sensor (Bank 2 Sensor 2)

The AF Sensor draws about 3 amps so check connections. The heater is a resistor between the B+ and HT terminals of the plug. On V engines there is also a AF relay to check.

I found the above info else ware on the web. I have the code intermittently on my 2001 V6 Sienna. If I ever get a day off I am going to troubleshoot mine and will report the results.

PS I may have answered this twice. I think I lost the first one.

Here is a listing of Toyota Specific Diagnostic Trouble Codes




BARO Sensor Circuit.


Accelerator Pedal Position Sensor Circuit.


Accelerator Pedal Position Sensor Range/Performance Problem.


Throttle Control Motor Circuit.


Magnetic Clutch Circuit.


ETCS Actuator Power Source Circuit.


Throttle Control Motor Lock.


Electric Throttle Control System.


Air/Fuel Sensor Circuit Range/Performance. (Bank 1 Sensor 1)


Air/Fuel Sensor Circuit Response. (Bank 1 Sensor 1)


Air/Fuel Sensor Heater Circuit Response. (Bank 1 Sensor 1)


Air/Fuel Sensor Circuit Range/Performance. (Bank 1 Sensor 2)


Air/Fuel Sensor Circuit Response. (Bank 1 Sensor 2)


Air/Fuel Sensor Heater Circuit. (Bank 1 Sensor 2)


Fuel Pump Relay Circuit.


Igniter Circuit Malfunction - No. 1.


Igniter Circuit Malfunction - No. 2.


No Crankshaft Position Sensor Signal - Engine Running.


VVT System.


Sub-Throttle Position Sensor.


Sub-Throttle Position Sensor Range/Performance Problem.


Turbo Pressure Sensor Circuit.


Turbo Pressure Sensor Range/Performance Problem.


EGR Valve Position Sensor Circuit Malfunction.


EGR Valve Position Sensor Circuit Range/Performance.


Starter Signal Circuit.


Boost Pressure Control Circuit.


Boost Pressure Low.


Boost Pressure High.


Stop Lamp Switch Signal Malfunction.


Cruise Control Main Switch Circuit.


ECM BATT Malfunction


Knock Control CPU.


Traction Control System.




Idle Air Control Valve Control Circuit.


OCV Circuit.


Wastegate Valve Control Circuit.


EGR Circuit.


EGR by-pass Valve Control Circuit.


Park/Neutral Position Switch Malfunction (Only For A/T)

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