O2 sensor [Re: Tools for diagnosing "Check Engine Soon" light?]

Before you buy that sensor, I'd buy a digital voltmeter (a cheap one) and test the O2 sensor to see if it and it's heater are functioning. On a 2003 V6 Mitsu engine, without VIC, the service manual shows 4 (four) oxygen sensors.

Right bank front, heater wires colour codes are red (+12)and blue-white tracer (grd) O2 sensor, blue (grd) and green (signal)

Right bank rear, heater wires colour code are, red (+12) and brown (grd) O2 sensor, pink (grd) and blue (signal)

Left bank front, heater wires colour codes are red (+12)and brown-white tracer (grd). O2 sensor, black (grd) and white (signal)

Left bank rear, heater wires colour code are, red (+12) and blue white-tracer (grd). O2 sensor, blue (grd) and yellow (signal)

BEWARE, this is for a 2003 V6 engine, should be the same as yours, but you never know. Check your local library, some times they have service manuals you can read through.

The heater is powered through the MFI relay, so your cars ignition will need to be in the "run" position to measure the voltage.

With the engine at operating temperature try this, you can test the O2 signal. The "signal" from the O2 sensor is a small voltage between .1 and .9 volts, and it should vary between these levels frequently. The manual states " While repeatedly revving the engine, measure the heated oxygen sensor output voltage"" it should be between 0.6 and 1.0 volts". If the sensor doesn't produce this voltage, it is most likely defective. You have three others to compare with.

The heater has a resistance (also measurable with the digital voltmeter) of between; Right bank, left bank rear,11 and 18 ohms at 20 degrees C, Right bank, left bank front,4.5 and 8 ohms at 20 degrees C.

Remember, this is for a 2003 V6.

The O2 sensor must be connected to the harness to measure the signal. Use small pins to pierce the insulation to attach your voltmeter.

Bosch sensors aren't junk. Bosch INVENTED the O2 sensor. everyone else just copied them.

Many of them are. Realize that the ones that Bosch sells to automakers are

*not* the same ones they box up and sell to consumer-level auto parts stores. The problem isn't universal across the Bosch aftermarket O2 sensor line, but it is a fairly widespread phenomenon that a Bosch aftermarket O2 sensor will fail early and require replacement again. I have seen it cause a great deal of headscratching and tailchasing ("It *can't* be the O2 Sensor, I just replaced it!").

Anyway, there's no reason to buy a dubious Bosch aftermarket sensor when consistently-better ones are available from so many other manufacturers.

True, but irrelevant.

DS

Thanks for the details. In the 2000 Galant 3.0 V6 (I believe it's a

6G72 engine) - I poked around yesterday to find only three O2 sensors. I took some pictures that will be available temporarily at this URL

Depending on your browser you might have to scroll horizontally or vertically to see three shots:

1. O2 Sensor Firewall Side (red rectangle around it)
2. O2 Sensor Radiator Side (yellow rectangle around it)
3. O2 Sensor Cat. Conv - this is vertically below the radiator side sensor.

I'm not sure if the third sensor is the pre-cat or post-cat? If there are three sensors, is #2 the pre-cat and #3 the post-cat?

I really think that there might be four O2 sensors, and that I haven't found the location of the fourth one yet.

Basically I need to identify "Bank 2, Sensor 1" according to the code P0155, which at the moment I'm guessing is the one I've shown as #2 - radiator side.

Thanks once again.

Himanshu

<snip>

First, thanks to: Richie Rich, hyundaitech, ray, lugnut, Daniel J. Stern, Nirodac, Eric F and Jim for replying to my posts.

Luckily "Bank 2, Sensor 1" translates to the easiest O2 sensor to acces - it's the one on the "other" cylinder bank (2,4,6), and sensor 1 is pre-cat. So it's the one in the front of the car when you open the hood. I've updated the pictures on the web page to show the locations of the sensors:

The wires on the O2 sensor didn't match the colors Nirodac posted - there was no RED at all. There's a white, light blue, a dark blue and perhaps a black or another dark blue. So I didn't know which ones to test voltages on.

I found a few more docs on how to test the O2 sensor and one of them said I should check continuity between two leads they showed on a harness. the diagram didn't was for a different model year, but I poked around on the problem sensor & found no continuity. Then I measured on those leads in two other sensors and I did find continuity on those leads. So it seems that this sensor may be dead.

Unfortunately none of the local stores have this sensor in-stock and I was thinking if I would have to order it anyway, then why not try and find one of the other sensor brands that were mentioned - NTK, NAPA, etc. But a search on the web shows practically only Bosch brand O2 sensors...only one site had "Walker" O2 sensors, which seemed like an off-brand. Any pointers to vendors that have non-Bosch O2 sensors?

Thanks.

Himanshu

<...snip...>

So today I was able to install the new O2 sensor in my Galant - eventually I got the best price at the local Mitsu dealer, believe it or not! It was a Denso O2 sensor Mitsubishi genuine part for $131. That is about $35 less than the local autoparts stores for a Bosch (which has received some negative feedback here).

Installation wasn't difficult except removal of the original O2 sensor

- man, was that a tough one to get out! I had the slotted socket wrench but still, it was tough to get it out. The Haynes manual said run the engine for a minute or two and that would make it easier to remove. So I did...and eventually got it out. Ofcourse, I put some anti-seize compound on the new one, even though there seemed to be some on the new one anyway.

The "Service Engine Soon" light didn't go away immediately, but I will check again tomorrow and if it's still on, I will get it reset and watch it. However, the car does seem to be running better - idling seems better, and the roughness in driving seems to be gone.

Finally - the old O2 sensor was completely blackened at the tip, somewhat like the one shown under "Oil Contamination" at Bosch's site:

Is there anything I should do about the oil contamination to prevent that from happening in the future? The tip wasn't wet, just dry black.

Thanks again.

I don't know if this is OBD-II or GM, but for my GM it takes 40 warmup cycles with no failures before the MIL goes off. IOW, clear the light and see if it comes back.

Ray

I've seen simple circuits on the Internet that will let you simulate an O2 sensor with a capacitor and a resistor. Personally, I wouldn't do it, except to save money on a new cat, but that's all it'll do for you. Do a goggle search for the info. I don't have it.

Mitsubishis,