P0155 code brings up MIL and VSC and TRAC OFF

[Capt_Spiff]

2003 Avalon: Last week the Check Engine, VSC and TRAC OFF lamps light following almost 2 years of trouble free motoring (84000 miles, but only the last 18K is mine).
The ODB scanner shows a P0155 code (O2 sensor, heater circuit, Bank 2 Sensor 1). A search in this forum shows it as the upstream one at the front, right near the oil filter.

RockAuto has it for $109 + $8 shipping and it arrives the next day. The Denso sensor is a perfect match and it comes with a tube of "never sieze" grease. The electrical fitting slips right thru the 22mm closed end socket, so it really was a 15 minute job.

Reset the MIL code, and the VSC lamp disappears as well.

I checked the old 4wire sensor (2 wires for the air/fuel element, and 2 wires for the small heater filiment) and sure enough the heater showed open on the ohmmeter. It's amazing how specific the new ODB systems are.

Now for the mystery: Does anyone know why Toyota would make the VSC traction control system shut down for an O2 sensor failure ???

Happy Motoring.

[eurobob1978]

Anytime a CEL comes on, the traction control shuts off. It has to do with toyota running a limp mode program that will typically get you where you need to go, at the expense of tweaked engine performance. Since the traction control lets the computer decided when to use gas and brake, it is disabled if there is a problem. I don't like the computer thinking for me on traction anyway.

[CraZySteve]

Originally Posted by Capt_Spiff

2003 Avalon: Last week the Check Engine, VSC and TRAC OFF lamps light following almost 2 years of trouble free motoring (84000 miles, but only the last 18K is mine).
The ODB scanner shows a P0155 code (O2 sensor, heater circuit, Bank 2 Sensor 1). A search in this forum shows it as the upstream one at the front, right near the oil filter.

RockAuto has it for $109 + $8 shipping and it arrives the next day. The Denso sensor is a perfect match and it comes with a tube of "never sieze" grease. The electrical fitting slips right thru the 22mm closed end socket, so it really was a 15 minute job.

Reset the MIL code, and the VSC lamp disappears as well.

I checked the old 4wire sensor (2 wires for the air/fuel element, and 2 wires for the small heater filiment) and sure enough the heater showed open on the ohmmeter. It's amazing how specific the new ODB systems are.

Now for the mystery: Does anyone know why Toyota would make the VSC traction control system shut down for an O2 sensor failure ???

Happy Motoring.

So did you try the Denso Sensor or the Bosch Sensor? - I just pulled the exact same code and am debating on saving a few $$ and getting the denso

[ChiTDI]

Denso all the way on that choice.
Search the forums and there's more success with the Denso than the Bosch.

[TedL]

Originally Posted by CraZySteve

So did you try the Denso Sensor or the Bosch Sensor? - I just pulled the exact same code and am debating on saving a few $$ and getting the denso

The one that came in the car from the factory is Denso.

[Capt_Spiff]

Yup, I bought the Denso from Rock Auto and it was identical to the one I removed (thinking that was oem). My reference to the electrical connector in my post above should have read: Fit thru the end of the 22mm closed end WENCH perfectly. I don't know about the BOSCH, but I stick with oem whenever able. Good luck, you'll feel empowered when the trouble light goes out!

[CraZySteve]

Originally Posted by Capt_Spiff

Yup, I bought the Denso from Rock Auto and it was identical to the one I removed (thinking that was oem). My reference to the electrical connector in my post above should have read: Fit thru the end of the 22mm closed end WRENCH perfectly. I don't know about the BOSCH, but I stick with oem whenever able. Good luck, you'll feel empowered when the trouble light goes out!

Sweet! I bought the Denso 234-9021 Oxygen Sensor from Amazon for $88.25 and because I am a prime member - 2 days later - Sensor! Still much cheaper than the Local Parts store ($126) and even RockAuto ($97 plus S&H) - So in the future check Amazon for Autoparts

Installed the sensor - it was a breeze - Antiseze on the threads, 7/8" combo wrench and some dielectric grease for the connector - Done!

2-3 days later the CEL and VSC lights cleared