So I finally got my 2003 Montero 3.0 2wd last week. Before I even got to the highway the CEL came on with p0174 p0154. I took it into the dealer to have the pcm flashed. After Flashing the pcm I replaced the oxygen sensor with a Denso direct fit and the CEL for p0154 came on within minutes. I plugged my scanner in and read he live data and it was showing no reading for the sensor bank 2 sensor 1. My only guess is that the dealer did not do the update properly. Any way I can diagnose this with my multimeter? I also was thinking it was due to the denso sensor so I replaced the bank 1 sensor 1 with a denso and it is working fine.

 

Swap known good B1S1 with troublesome B2S1. If you loose reading on Bank 1 at this point - you've got a bad sensor; if you got no change from previous situation - you have an issue with PCM reading sensor output or an issue with the wiring harness to the bank 2 sensor 1.

 

Thanks, I went ahead and swapped it, I had to break off a small part of the clip to get it to go in but it was needed. I also returned the sensor and got a new one and still nothing. I provided an additional ground source to the black wire are the harness connection of the oxygen sensor and still nothing. So I went ahead and purchased a pcm, immobilizer and key with the ignition switch off of ebay. I can only hope at this point but I will follow up with my results. Anyone know where the immobilizer is? Also will I need to have the vin programmed into this pcm or does this pcm not store vehicle vin info?

 

So I ordered a pcm, immobilizer and key from Ebay and installed it.. Still the same sad story no readings. I went ahead and got another oxygen sensor this time a bosch and actually got some nominal readings when heavily accelerating. Still no fix. How or what wires should I be looking to diagnose off the harness?

 

It sounds like you have a problem in the wiring harness. Look for the manual on the sticky post at the beginning of the Montero forum page.

 

I found the service manual online but dont see the wiring diagrams specific for the oxygen sensors or even the pcm for that matter. Anyone have this page or section?

p.s. just found it but its diagnosis stops at the oxygen sensor connector and doesnt continue to diagnose anything but the actual sensor.

 

Look up on YouTube Scannerdanner and O2 wiring diagnostics. That may give you some ideas of how to go about testing the wiring harness. In fact he does have one for O2 on the Montero

 

Just a thought. Is your bad O2 sensor is an aftermarket or OEM? I wonder if this can be one of those cases where PCM use voltage bias on the O2 sensor and it has to use the OEM only sensors?

 

I used an aftermarket Sensor and is working just fine. From RockAuto.com and about 30 bucks vers. 180 from the Steelership.

 

I've done OEM sensors on my '01 Monty and the aftermarket ones. Both kinds worked well so far.

npreza, measure voltage on the O2 sensor wire (between sensor wire and battery negative), then between sensor ground and battery negative.
This is on the sensor circuit, not the heater circuit. Do it first on the know good sensor, then repeat on the one you suspect bad. Post the results.