Mitsubishi Montero & Montero Sport This sport utility vehicle offers more size than the other Mitsubishi SUVs, but manages to keep a sporty look and comfortable feel, unlike many larger SUVs.

Multiple codes on Montero Limited 2002

Old 01-08-2019, 02:40 PM
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Join Date: Jan 2019
Posts: 2
Default Multiple codes on Montero Limited 2002

Hi guys, first post here.
I recently purchased a 2002 3.5l Montero limited. When I got it, the ABS light was on. Replaced the reluctor rings and sensors and it's been fine ever since. Put quite a few miles on it in the short time we've owned it and also replaced the front wheel bearings.

Last week the Service Engine Soon light came on. Today I picked up an OBD II reader and it's throwing up the following errors:

p0431 - Warm Up Catalyst Efficiency Below Threshold (Bank 2)
P0155 - O2 Sensor Heater Circuit Bank 2, Sensor 1
P0170 - Fuel Trim Bank 1
P0125 - Insufficient Coolant Temperature for Closed Loop Fuel Control

P0455 - Evaporative Emission System Leak Detected
p0441 - Evaporative Emission System Incorrect Purge Flow

Being an idiot, I cleared the codes, desperate to see if my reader worked ok with the Mitsu. So no freeze frames. However, the check engine came back on and the first code stored after idling for 5 mins was the P0155.

Where would you guys start? I'm thinking replacing the upstream O2 sensor for Bank 2 and checking for vacuum leaks around the inlet gasket, maf, etc. Seems sensible to me, but what do you guys think? My previous cars have all been simple 80's things with no computers or lambda sensors etc, so although I was good with them, a lot of the stuff in this car is super future and I haven't seen that before.

Old 01-08-2019, 04:00 PM
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Join Date: Oct 2015
Location: Northern VA
Posts: 281

I can't recall which is Bank 1 or Bank 2 (drivers vs passenger). I had a cracked exhaust manifold on the passenger side which I believe contributed to some of the emissions codes the engine had prior to loosing 2 rod bearings. The cracked manifold could not be seen behind the heat shield.

My rebuild thread is linked below. Somewhere in there I have pictures of the cracked exhaust manifold and the china replacement manifold. I also replaced all of the O2 sensors and have pictures of those and the ones I used.

Wish you good luck! Hunter will likely soon chime in and offer sage advice.
Old 01-09-2019, 01:56 AM
Senior Member
Join Date: Oct 2004
Location: Washington State
Posts: 1,311

With that many codes, some of them might be secondary. So your best bet is dealing with them one at a time and then tackling the ones that come back.

Bank 1 is the left side of the engine when viewed from under the hood (passenger side). If you get a specific code for O2 sensor (Bank 2 Sensor 1), that's where I'd start diagnostics. It is possible you have a bad sensor or a bad wiring to it. First thing to do is to check if you have a break or damage in the O2 sensor wiring harness or a bad plug connection. You could swap left to right side sensors to see if the error "moves" to another side or stays in the same bank. This will indicate a bad sensor or a bad wiring to sensor.

Good call on checking for vacuum leaks. The Bank 1 fuel trims can be coming from that. Most likely your Bank 2 fuel trims are close to being out of whack, but Bank 1 got there first and set the code.

I have not had to deal with the Evap codes on a Montero, but on another vehicle bad (cracked) hoses to the canister were causing leaks in Evap system and triggering those codes. Look around and check those things. You may have a problem with rubber hoses at or near the fuel tank (vapor venting). There is also a relay on Evap system that may have gone bad and causing a bad reading in it.

Try to find a factor service manual for your Montero. That will give you step by step diagnostics which will help to narrow down the suspected bad parts. There is a discussion in the forum "Why don't you have a Manual". Read through it. It has (had) many links to places where manuals were available for download in the past.
Old 01-09-2019, 10:02 AM
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Join Date: Jan 2019
Posts: 2

Thanks for the replies. Over the weekend I'm going to start with the Bank 2, Sensor 1 and go from there. Since wiping the codes, I've driven it a little bit and the two codes that have reappeared have been first, the O2 sensor, then after that the Cat efficiency code. I'm hoping this points to the sensor being the main issue and not the pre cats. I did some reading last night and found a few threads saying that the Cat Efficiency Code is almost always a sign of a dead Cat... hopefully not, and it's just secondary.

Other than this and a slight oil leak, the engine is running really nicely.
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