OK, so, with the help of a friend who's a mechanic, I was able to get the 02 sensor replaced. We did run into an interesting issue with the wiring harness on the Bosch BS15599 replacment sensor. The harness did not fit smoothly into the existing harness and at first we thought I had the wrong part. (the sensor itself looked slighly different than the denso, e.g. the tip of the bosch was a little thinner.) Once we confirmed that we in fact had the right part, my friend bent the old harness plastic a bit and was able to plug the sensor in. Using his portable computer thing (that's a technical term) he said it looked like the sensor was working fine. So thanks! In the end this thread and your advice saved me about $300 and it only cost me a lunch and a few beers for some additional labor!

 

2 words.... F UCK BOSCH

 

I had no problems whatsoever with my Bosch replacement. Possibly your harness from the truck was slightly warped from heat? I know It was hard for me to get my old one off.

Glad you got it taken care of though, charging $500 for 45 minutes of work is terrible.

 

I had a heck of a time with this one (Upstream, Driver's side) even though I had the special Oxygen sensor tool. I think an open ended 22mm wrench would have worked better, but it has to be thin and either very long or very short. This is the hardest of the four O2 sensors to replace. My hands were barely small enough to fit in the space and I had a heck of a time getting leverage once I had my hand wedged in there.

Before you buy the part ($125 at autozone), you can remove the connector and use an ohm-meter to check for continuity between pins 2 and 4 (I believe these are the two right hand side pins in the connector). P1055 should result in an open circuit between these two pins. If you are getting a resistance value between them, the problem is not the sensor, it is either in the wiring harness or the PCM (Powertrain control module).

Note also that both AdvanceAutoParts and Autozone will either sell you the single "OEM" sensor for around $120, or sell you a $60 - $75 sensor, but it requires that you replace BOTH of the upstream or downstream sensors (so your total cost is $120 - $150), and you have to splice into the existing cable (the cheap ones don't come with the connector).

For reference,

Codes P0130 to P1035 are for Bank1, Sensor1, which is Upstream Passenger Side
Codes P0136 to P1041 are for Bank1, Sensor2, which is Downstream Passenger Side
Codes P0150 to P1055 are for Bank2, Sensor1, which is Upstream Driver Side
Codes P0156 to P0161 are for Bank2, Sensor2, which is Downstream Driver Side

Autozone will loan you the special wrench adapters to remove the sensors (they charge your CC, then refund it).

I found it interesting that my gas mileage actually improved while this sensor was on the fritz. Not by much, maybe 1 mpg.

From the manual :

DTC P0155: Heated Oxygen Sensor Heater Circuit (bank 2, sensor 1)

CIRCUIT OPERATION • Power is supplied from the MFI relay (terminal No. 1) to the left bank heated oxygen sensor (front) heater. • The PCM (terminal No. 10) controls continuity to the left bank heated oxygen sensor (front) heater by turning the power transistor in the PCM "ON" and "OFF". TECHNICAL DESCRIPTION • The PCM checks whether the heater current is within a specified range when the heater is energized. DTC SET CONDITIONS Check Conditions • 60 seconds have elapsed from the start of the previous monitoring. • Engine coolant temperature is higher than 20°C (68°F). • While the left bank heated oxygen sensor (front) heater is on. • Battery positive voltage is at between 11 and 16 volts. Judgment Criteria Heater current of the left bank heated oxygen sensor (front) heater has continued to be lower than 0.6 ampere or higher than 7.5 ampere for 4 seconds. TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: ) • Open or shorted left bank heated oxygen sensor (front) heater circuit. • Open circuit in left bank heated oxygen sensor (front) heater. • PCM failed.

2002 Montero Limited 58,000 miles

 

Ok so I just finished replacing my left-front O2 sensor, and what blew me away the most is how much the dealership wanted to perform what took me all of 45 mins!!? And might I add, the reason it took so long was that I was trying to get the plastic clip off the old O2 sensor to put onto the new one.

$450+tax for an O2 sensor and that doesn't even include labor!! My local parts supply store was no better coming in at $312+tax. Am I the only one who is simultaneously shocked, baffled and disgusted by this? When the parts manager at my local (deliberately unnamed) Canadian dealership told me how much it would cost, I almost blurted out "Are you f*#$ing mental?".

Don't they realize that the very same DENSO part retails for $83 at internet parts guys like rockauto etc. Even with shipping and import duty and currency conversion(to Canada), that was <$120!!

Now I know that the dealership has to charge a price $x because Mitsubishi forces them to buy at price $y from them, but 4.5 times as much as the next alternative!! Mitsubishi NA, you are screwing over your dealers!
Ok Rant over, back to the technical.

For whoever else wants to attempt this, yes a LONG HANDLED 22MM open wrench worked. Rather well actually, given my big fat hands. My standard O2 sensor socket did not work, because then there was insufficient room for my ratchet at the end of it. Something like would also work well, perhaps even better than the wrench.

One more point for those that have such a wrench, the Factory Service Manual says tighten to 44 ± 5 N⋅m (33 ± 3 ft-lb), assuming you can get your Torque wrench on it.

Remember kids, if something is worth doing, it will be on the internet somewhere.

 

I'm fixing to replace my O2 sensors because of the CEL. On the Autozone website it has for California emissions with left and right, upstream and downstream sensors. While Federal emissions only has upstream and downstream. Am I safe to assume since I bought this truck brand new in Louisiana it doesn't have Cali emissions? And is that true what is written in post #2, both of the downstream sensors should be replaced and not just the one throwing the code? I'd have to buy 3 sensors the two downstream and one upstream on the drivers side.

Thanks

 

Hello again! My '02 Monty XLS has a "pending" P0155 error. I used my iPhone with an GoPoint app because I wanted to see real time gas mileage.

This "Pending" code showed up for the first time and just the day before I had the transmission fluid changed at a Mistubishi dealer who also performed a PCM reflash. The battery was probably disconnected as well because we lost all radio stations and the clock was reset.

I did a clear check engine light (the actual CEL was not on) and today I plugged my iPhone back in and there is no "pending" code after 50 miles or so of everyday driving.

Could the P0155 have been triggered by the PCM update and battery disconnect?

 

As a follow up, since I cleared the "pending" code it has not returned. I have to assume it was triggered by the PCM reflash or battery being disconnected...