2002 Mitsubishi Montero XLS 3.5L Engine Codes

[thedeatons]

Hey guys... Every once in a while we get an SES light on in the dash. It goes away after a fee hours. The computer has a couple stored codes in it. Just wondering what would cause these codes and the SES light to come and go like this?

Codes:
P0171
P0134

See attached pics of the printed code.

James

 

[RyanY]

I would say it's likely a bad O2 sensor, but I would download the factory service manual and follow the diagnostic instructions for those codes before I threw any parts at it.

 

[Michael Brown]

You can get the FSM in my link below. It is probably the sensor as I just replaced mine as well. You can buy sensors from Rock Auto, eBay or OEM. I bought a set from eBay to replace the bank 1 sensor 1 issue. Working now with no issues for a few weeks. Make sure to clear the code with a cheap OBD reader once you install the new sensor.

FYI, the O2/diesel injector socket set from Harbor Freight worked great to remove this without tearing the engine bay out. You have to disconnect the wire and remove it from the tie-down spots along the way, but the sensor can be easily reached from underneath the passenger side.


In the meantime, the engine will just run rich to compensate for not knowing the O2 values leaving the engine.

 

[plh]

Denso is OEM brand

 

[coffeegoat]

I had similar codes a while back and being the lazy bum I am I just replaced all of them. I seem to recall it was only ~$150 or so for the OEM parts on amazon, and I think only an hour or so to replace them all. I didn't even need to put the truck up on ramps or jacks (though YMMV). I saw a mild (1-2) MPG improvement post install and the engine does seem to be more responsive, but that's probably all in my head.

When I was researching it what I found was that the O2 sensors just wear out over time, their expected life is only 8-10 years and these trucks are pushing 15-20 in most cases. They don't usually fail flat out, they just start slowing down their response and giving less accurate readings. This is common with all electrochemical devices, but it's very common on high temperature oxygen conductors like O2 sensors. My day job is actually working on these sorts of devices for fuel cell and electrolysis systems and we spec %/khr degradation rates for all of our systems and it's actually pretty difficult to get these things to run for >5 years.

The other thing to watch for if you replace the sensors and you still get the "too lean" code is cracked manifolds, they commonly fail on the 3.5 engines. If they start drawing in air it tricks the O2 sensor into thinking the engine is running lean and it'll feed more fuel to compensate. Replacing them is a bit of a hassle, repairs have only kind of worked...

 

[Salonika]

If you have no history on the age of your o2 sensors it is worth it to replace them. Diagnosing other related problems is easier if you can trust what they are telling you. If you do replace them make sure not to contaminate the sensor tip during installation.

 

[davidgreams]

Either the 4 runners or Montero would be a great choice, both infinitely more reliable than a disco. I think there are many solid explanations and budget expectations of 4 runners throughout Reddit. Regarding the Montero, let me direct you to a previous post of mine weighing the pros and cons of a gen 2 and 3 Montero.

If he is really considering the Montero make sure he:

1. Buys a limited, not xls.
2. Runs the centre diff through 2wd through to 4lolo on gravel or dirt.
3. Outside of that, tell him to check out the links included in my gen 2/3 post.

 

[thedeatons]

Either the 4 runners or Montero would be a great choice, both infinitely more reliable than a disco. I think there are many solid explanations and budget expectations of 4 runners throughout Reddit. Regarding the Montero, let me direct you to a previous post of mine weighing the pros and cons of a gen 2 and 3 Montero.

If he is really considering the Montero make sure he:

1. Buys a limited, not xls.
2. Runs the centre diff through 2wd through to 4lolo on gravel or dirt.
3. Outside of that, tell him to check out the links included in my gen 2/3 post.

I think you may be in the wrong thread??

James

 

[Michael Brown]

I think he has been copy and pasting Reddit posts here