o2 sensor problem? Code P0154 and P0174
 

03 Montero Sport XLS 3.5L

So my Service engine Soon light came on the other day and I went to AAP and used the OBDII reader. It gave the following codes:
P0174 System too Lean (Bank 2)
P0154 o2 Sensor, CKT No Activity (Bank 2 Sensor 1)

I looked under the truck and I noticed there are 2 oxygen sensors on the passengers side where the 2 exhaust pipes coming from the engine combine into 1 pipe. There is also an o2 sensor on the drivers side.

Which sensor is bad? I am not sure what this code is referring to. Any ideas on how to fix it?

Thanks

RE: o2 sensor problem? Code P0154 and P0174
 

theres actually a software upgrade that may deal with that issue. It may still require O2 sensor replacement, but the bulletin that deals with it is 04-13-002rev.
try a mitsu dealer for that update before swapping any parts.

RE: o2 sensor problem? Code P0154 and P0174
 

Ok thanks, I'll check with the tomorrow...

I stopped by the dealership this morning to find out what Bank 1 and 2 are.
On the 3.5L the sensor positions are as follows:
Bank 1 - Passenger side
Bank 2 - Driver side
Sensor 1 - Upstream
Sensor 2 - Downstream (after converter)

I'll probably check for vaccuum leaks tonight and if I can't find a leak I'll try changing the o2 sensor...

RE: o2 sensor problem? Code P0154 and P0174
 

the problem with the code is that it INCORRECTLY identifies the O2 sensors. In other words, there may be a dead one, but it is NOT the one indicated.
thats part of the software update.

Just replaced both upstream 02 sensors, help!
 

I bought a 2001 Montero sport 3.0 L and got p0154, p0174, and p0421 and was advised to replace the two upstream sensors. It did good for a day and a half and then I got a SES light again. I have a feeling that the truck needs an upgrade by a dealership.

The upstream O2 sensors controls how much fuel is fed into the engine via fuel injectors. Since your Bank 2 Upstream O2 sensor has no activity, the PCM does not now how much fuel to measure out. The System Lean code is most likely related to the malfunction of the O2 sensor. First check the wiring to the sensor. If you are lucky, the O2 sensor got unplugged accidentally. Another possibility is that the wire to the sensor got severed by some road debris, or the sensor burned out.