How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Dan Your Own Question
Dan, Technician
Category: Toyota
Satisfied Customers: 24206
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
Type Your Toyota Question Here...
Dan is online now
A new question is answered every 9 seconds

Toyota: P0155..under warranty..the O2 sensor replacement..error codes

This answer was rated:

I have had error code P0155 on for a few weeks now. I have had this code is the past and had Toyota replace O2 sensors under warranty. Even after the O2 sensor replacement the error codes still came up. I started to suspect the K&N cold air intake I had added so I called K&N and they told me I had the wrong pipe. I shipped the old one back and the new one they sent was necked down before the MAF sensor. That fixed the problem and the code was cleared for a couple years or so. It came on again recently. I am using a bluetooth device to monitor the sensors and the O2 sensors seem fine. I will try cleaning the MAF sensor tomorrow. Any ideas?
It is a 2002 Toyota Tundra V8 .

Welcome to JustAnswer, my name is XXXXX XXXXX I'm here to help get your problem resolved. Ask follow up questions, thanks.


This code is related to heater circuit on oxygen sensor so mass airflow sensor cant be the cause.At the oxygen sensor, check for the correct heater circuit resistance. 11-16 ohms should be present. At the Red wire of the oxygen sensor, check for 12 volts when the key is in the On position. Check the solid Yellow wire of the oxygen sensor for an open or short to ground between the sensor and the engine control module.



P0155 Heated Oxygen Sensor (Bank 2 Sensor 1) Heater Circuit Malfunction

Possible CausesSetting Conditions
  • HO2S heater connector is damaged (check pins for damage, and for moisture)
  • HO2S heater control circuit is open, shorted to ground or shorted to voltage
  • HO2S heater power (12v) circuit is open (check power circuit from EFI relay)
  • HO2S heater has failed
  • ECM has failed
Engine running; and the ECM detected that the Bank 2 Heated Oxygen Sensor 1 (HO2S 2/1) heater current exceeded 2 amps, or it was less than 0.25 amps.

This code sets in 2 Trip(s).
This code will turn on the MIL (Malfunction Indicator Lamp)

Customer: replied 6 years ago.
Thanks for the info sir, I'll take your advise and make these checks.
No problem....dealership probably just replaced common parts without testing. let me know if you run into questions. Thanks.
Dan and 5 other Toyota Specialists are ready to help you
Customer: replied 6 years ago.
Hello Dan,
Thanks again for your assistance. I had a heck of a time disconnecting sensor 1 from bank 2 due to the location of the connector. I had to snap the clip that mounts the harness to the engine block and then pull the harness down to where I could get a good enough grip to disconnect the 2 connectors.
I found that the heater element was open within the O2 sensor. I also had sensor 2 in bank 2 with the same failure. Sensor 2 failed not long after I requested info from you.
I replaced both O2 sensors last weekend with non OEM replacements ( BOSCH O2 sensors from Auto Zone )
So far so good, the faults of P0155 & P0161 have not occurred again.
Any ideas to what can cause OEM O2 sensor's heater elements to open. Exhaust temperatures too high? Using the wrong fuel injector cleaner additives? Or just garbage OEM O2 sensors?
Rodney Martin

I think just happened to get some poor sensors, they dont usually continue to fail like this and nothing should cause them to fail early.