First Montero: 2002 Gen 3 XLS

[epyonxero]

Been lurking and researching for a while and just picked up a 2002 Gen 3 with 160k miles on the clock about 2 weeks ago. Vehicle was clean and ran well with minor issues and no CEL codes but no service history so Im catching up on all the high priority maintenance.

Work Ive done so far:
Sunroof motor fix - the day I brought it home it was stuck open
Temp gauge re-solder
Oil change
New air filter - broke the plastic air box tabs in the process
Defogged the headlights

Planning to do the timing belt/water pump and a diff/transfer fluid change next.

 

[epyonxero]

Yesterday was my first chance to get out to the desert and try out the Montero offroad. It seemed to handle everything with no issues and was able to keep up with my friends.

However there is a new problem: on the drive out, which was my first extended time on the highway, the CEL came on and stayed on the rest of the day. I checked the codes when I got home and they were:

P0137: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2); Oxygen sensor(rear) low
P0171: System Too Lean (Bank 1); Fuel trim too lean

Searching the internet I see these could be caused by vacuum leaks, bad O2 sensors, and fuel pump issues. Can anyone advise how best to narrow down the source? Does the fact that the code occurred while under highway load indicate anything? Also, Ive seen a few places that the butterfly valve shaft o-ring may cause a vacuum leak but I cant find it on my engine; all the photos Ive seen are from the 3.8.

 

[steevo_102]

Congrats on the the Montero and welcome. You wasted no time hitting the trails lol I got my Montero 2 months ago and still haven't gone for fear of being unprepared. I think you might've encouraged me to go this weekend. And I see you went on street tires as well, so I really have no excuse.

on the drive out, which was my first extended time on the highway, the CEL came on and stayed on the rest of the day. I checked the codes when I got home and they were:

P0137: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2); Oxygen sensor(rear) low
P0171: System Too Lean (Bank 1); Fuel trim too lean

I've had both these codes as well when I first got my Montero. After diagnosing I replaced the o2 sensor and the code went away. Buy the original Denso o2 sensors that came with from factory...aftermarket ones get finicky with these cars.

 

[epyonxero]

Congrats on the the Montero and welcome. You wasted no time hitting the trails lol I got my Montero 2 months ago and still haven't gone for fear of being unprepared. I think you might've encouraged me to go this weekend. And I see you went on street tires as well, so I really have no excuse.


I've had both these codes as well when I first got my Montero. After diagnosing I replaced the o2 sensor and the code went away. Buy the original Denso o2 sensors that came with from factory...aftermarket ones get finicky with these cars.

Well originally my plan was just to get out into a bit of sand and test out the 4wd but when I got there, the guys had a full route mapped that they said wasnt too crazy. It had a little bit of everything but Im glad I did it because it showed me what a stock Montero is capable of.

I ordered a new Denso O2 sensor. On my OBD2 reader, all of the other sensors look fine so hopefully its just one bad one causing a false lean condition.

 

[MontySquareo]

i had the same code (p0171) i have a nice code reader so I was able to graph the o2 sensor voltages, and I discovered that when accelerating into the highway one of the 02 sensors would decide to just constantly read lean, but the other sensor on that bank would start to read rich as the computer tried to fix the supposed lean condition. replaced the 02 sensor that read lean and everything has been good since

 

[Justice R]

The SOHC 3.5 does not have butterfly valves so no need to worry about those on your model year. You can check for vacuum leaks with an unlit propane torch if you still suspect a vac leak. Open the valve and disperse the propane around the intake while the engine is idling if idle speeds up from the propane, you have intake leak.

concur with the O2 sensor comments. Replace with Denso.

 

[epyonxero]

The SOHC 3.5 does not have butterfly valves so no need to worry about those on your model year. You can check for vacuum leaks with an unlit propane torch if you still suspect a vac leak. Open the valve and disperse the propane around the intake while the engine is idling if idle speeds up from the propane, you have intake leak.

concur with the O2 sensor comments. Replace with Denso.

I hadnt heard about that method, thanks for the tip.

 

[Michael Brown]

You can also use a spray can of Carb Cleaner or starting fluid in place of propane.

 

[steevo_102]

Well originally my plan was just to get out into a bit of sand and test out the 4wd but when I got there, the guys had a full route mapped that they said wasnt too crazy. It had a little bit of everything but Im glad I did it because it showed me what a stock Montero is capable of.

I ordered a new Denso O2 sensor. On my OBD2 reader, all of the other sensors look fine so hopefully its just one bad one causing a false lean condition.

Gotcha. For me, I have nobody to roll with so when going solo, I wanna make sure I'm well prepared. Otherwise I would've tried it out stock.

The original o2 should resolve the issue.

You can also use a spray can of Carb Cleaner or starting fluid in place of propane.

Yup. This is what helped me identify the vacuum leak on the butterfly seal on mine.

 

[epyonxero]

Just got the Montero back from having the timing belt + other recommended front end maintenance done, had the mechanic replace both downstream O2 sensors while he was at it. The old parts look like theyre in good shape. The pulleys and water pump were OEM but the timing belt was Gates so there must have been a belt job done at some point. Going to keep an eye on the O2 sensor voltages but right now the CEL light is out.

 

[epyonxero]

I wasnt planning on upgrading the head unit so soon but not having Bluetooth sucks so I decided to bump that up the priority list. At first I was going to get the cheapest bluetooth head unit I could fins but after doing some research I decided to go with a full featured double din with wireless android auto and camera support.
ATOTO F7

There are a few posts about moving the climate controls to a lower slot and fitting a double din in the 3rd Gen Montero but they all seem to be Limited models which have digital temp and vent controls which are easy to move. The XLS has push-pull cables which are a PITA so I decided to take some photos and make a post for anyone who might want to do this on an XLS in the future.

When the climate controls are in the lower din, the path of the temp cable is blocked by the steel center console frame. At first I tried routing the cable around the frame and attaching it with zip ties. This was quick and worked well enough but I wasn't sure if I was still getting full range on the knob throw and I was worried about long term damage so I decided to drill a hole in the frame to give the cable a direct path.

Theres just enough space below the welded nut to use a ⅞” hole saw, the other side of that nut is where a grounding strap attaches so make sure you remove that before cutting. I added a rubber grommet and ran the cable through to the control arm. The temp control moved much freer than when the cable was routed around and it seems to have full range. I ended up reattaching the grounding strap on the front side of the frame.

 

[EpicPlanet]

A year later... How's the Montero?