P1133, but which o2 sensor would it be?

[jmgtp]

2001
LegGT
2.5 / 5mt
50k miles

I fired the car up yesterday afternoon and had an instant CEL. Had it scanned at AutoZone and it came up as P1133:

insufficient switching sensor 1 or bank 1, sensor 1

An o2 sensor, no biggie. I've only been under this car a handfull of times and paid no attention to how many o2 sensors we may have. I imagine there are 3. 1 on each bank and one post cat? As indicated by the P1133 description the faulty sensor is on bank 1 and/or sensor 1. Which bank is bank 1 or which sensor is sensor 1? passenger side or drivers side?

Also, what seemed odd to me is that the scanner revealed that 2 codes existed however they were both P1133. If I am correct in assuming we have an o2 sensor on each bank could this mean both are bad? Perhaps they are both on the same circuit and the wiring is bad? Then again could just be same code in there twice for no particular reason.

Thanks!

[jmgtp]

Well after hopping around on the internet for a while I determined it is a 2 sensor system, 1 before cat 1 after cat. And P1133 referes to the one before the cat.

I replaced the pre cat o2 sensor. Pulled the negative battery cable for 5 mins. Fired it back up and the light came back on :(

Any ideas? The wire harness doesn't look at all degraded/heat damaged. And I measured (with key on) 12v at one of the terminals. At a loss here.

Going to try to drive it around for a few minutes in hopes that this light will disappear but that seems unlikely.

Edit: more info

This what I measured at each of the 4 terminals of the front o2 sensor harness with key on and engine off.

http://img155.imageshack.us/img155/8530/harnessum6.png

The 12v at the one heater terminal is the only one that makes sense to me. How would the signal and ground wire read 3.8v and the other heater wire 3v? Does anyone know what these values should be?

[Huffer]

5 mins may not be enough time for the ECU to reset. My car varies between 5 mins and 15mins.

Try clearing the code using a scanner, then see if it comes back.

[jmgtp]

Thanks for the reply.

I actually let the car sit overnight with the battery disconnected but the light came back upon start. I'm still going to have it cleared with a scanner...

[Huffer]

Did you solder your wire connections, and did you solder the right ones?

Check your rear O2 also - when I replaced my front O2 I kept getting the code because my rear O2 was messed up as well - the sensors verify their signals against one another, so without a reference point...

[jmgtp]

I did not solder them. The bosch unit came with a weather tight junction box and what they call 'posiconnectors' or something like that. They seem to get the job done. With an ohm meter I had continuity across the heater element terminals so I know that they are at least wired correctly.

So the rear o2 sensor can throw a P1133 as well? I thought the code was specifically for the front. I was just under the car and with an ohm meter checked for continuity across the rear o2 heater and that checked out ok - not to say that is any indication of the condition of the o2 sensor. I will probably pick up a rear o2 and slap it in, keeping my fingers crossed that it does the trick, although I hate throwing parts at it blindly.

Again thanks for the response and keep it coming! I've been having a tough time finding info/help on this issue anywhere on the net.

[jmgtp]

I replaced the rear o2 sensor today, pulled the battery for 10 mins... fired up... and CEL remains.

At a loss as to what could cause a P1133 (o2 sensor malfunction) other than a bad o2 sensor or sensors? Wire harnesses do not appear at all damaged.

The replacement sensor are the universal type that need to be spliced with part of the harness from the original o2 sensor.

After some prodding with an ohmeter I wired the universal up under the assumption that on the original:

Blue Wire = signal
White Wire = ground
Black Wires = heater element (polarity should not matter)

ideas? anyone?

BTW had the codes read again at Autozone and it still has P1133 in there two times. I asked to have them cleared and the employee refused stating that it was illegal for them to clear them, never heard that one before!

[Huffer]

Yeah, Autozone cannot clear codes - it can be considered tampering if there are pending codes, which are cleared, and then the car is sold or echecked.

As for your issue - are you sure you have the wires matched up right?

I'm at a loss for this one also. On the earlier gen (BD) there are 3 wires, 2 black, 1 white, and they match the universal Bosch O2 sensors. So I never had any problems with the heater circuits or readings.

I think you may have to plonk down some change and see a dealership... outside shot, maybe the ECU map is fried?

[jmgtp]

As far as I know they are wired correctly...

I removed the original o2 sensor and used a propane torch to heat it. While heating I used an ohm meter against the sensor body (ground) and the other lead against the blue wire and observed DC voltage increase when I applied heat and decrease when I removed heat. Hence, this is how I determined the Blue wire must be the signal wire. Using the same process I grounded using the white wire and read the same voltage range, hence the white wire is ground.

I had continuity across the two black wires on the original sensor and determined these must be for the heater. The Bosch universal unit came with directions stating the heater element is not polarized, so it does not matter how you wire them so long as you use the two wires intended for the heater.

With the above information I wired the original o2 harness to the universal sensor/harness - of course nothing has 100% certainty, but given the above tests/process of elimination I am 99% certain that they are wired correctly.

Both sensors used the same color scheme wires and I tested both with the same process as described above.

I believe I must either have a bad aftermarket o2 sensor, an incompatible aftermarket o2 sensor, bad ecm or bad wiring in the engine harness.

I've read at least 1 post on NASIOC mentioning a fried ecm after the o2 sensor went bad - some kind of ecm defect. I'd hate to throw an ecm in it without good reason though.

The problem I have with taking it to the dealer is that they will charge a diagnostic fee of at least $75 just to take 30 seconds and pull the code with a scantool. When they see P1133 they'll insist on replacing the o2 sensors to the tune of a few hundred dollars. When that doesn't pan out they'll replace the ecm and so on. I fear they'll throw parts at it till it is fixed but the problem is they'll still tell you everything they replaced was bad and stick the bill to you even though in all likelyhood the only bad part was the last one they replaced.

I feel pretty stuck right now. Can't seem to find any info on the net pertaining to this particular problem.

Sorry that got so long... just frustrated.

Any info, please share.

Thanks!

[jmgtp]

With the universal Bosch o2 sensor still triggering a P1133 CEL I decided to do a little more hands on research.

I checked the resistance across the original front o2 sensor and the circuit was open, indicating a for sure bad heater element and almost definetly the cause of the initial CEL.

I then measured resistance across the Bosch heater element and found 9.6 Ohms which seems reasonable.

As a control I measured resistance across the original rear o2 sensor element and found 5.7 ohms.

Since the Bosch unit didnt wipe out my CEL I decided to wire in the orignal rear o2 to the front. When I started the car up the CEL did not light! At least for 10 seconds. However, I considered this progress since the Bosch sensor made the check engine light instantanesouly upon start. I disconnected the battery and tried again using the rear o2 in the front and again it took about 10 seconds before the light came on.

At this point I determined that the car was rejecting the Bosch unit as incompatible right from the start and rejecting the original rear o2 within 10 seconds when it found the reading to be out of spec since the design is different (see pic below).

So I dropped another $100 at sparkplugs.com for an OEM w/connector Denso o2 sensor and I think it will do the trick. Just waiting for UPS to drop it at my door. If the light goes out then I will have to take up a fight with Pep Boys to return the Bosch sensor since it is very apparent that it is not compatible with my vehicle... I have a feeling I'll need a lawyer to get my $ back though!

Moral of the story: Don't go cheap on parts! OEM is the way to go from get-go.

Click for larger pic.
http://img506.imageshack.us/img506/3466/allo2sidebi5.th.jpg (http://img506.imageshack.us/my.php?image=allo2sidebi5.jpg)

[BAC5.2]

Here's what you should do, plug the sensor in, start the car. Check voltage when the sensor is plugged in and the car is warmed up. It'd be best to check voltage at the top connector. Use a needle probe and slide it into the connector. Be sure to check the O2 sensor side of the connector AND the car side. If the wiring is fine up to that connector, then great. Replace the extension harness and be done. If it's STILL bad, then you need to trace it back further.

If that checks out OK, then work back towards the ECU.

What can often happen is that a connector will corrode and short across the connector.

It looks like that's what has happened somewhere based on the ground voltage in your picture. Ground at the connector should have been zero volts, so it looks something is jacked. That's why it threw PO1133. Signal matches ground, so the ECU sees no variance in voltage. I wonder, though, why it didn't throw a PO1131 for a circuit malfunction (short circuit).

I was running a Bosch Universal sensor in my Legacy, and it worked just fine. I'd look into the wiring before you fry the new OEM sensor.

[BAC5.2]

Oh, and the universal sensor you have is wrong.

There is a universal sensor that is designed like the OEM piece. I had the same sensor as my first sensor in the Legacy. Upon startup, it was junk. Car didn't run properly AT ALL. I went back to autozone and looked at all of the "universal" sensors, and picked the one that looked closest to stock. I think it was for a 99 Nissan Maxima or something. The posilock box is also junk. Hardwire it.

Not all "Universal" oxygen sensors are the same.

[jmgtp]

Regarding the voltages I measured... I spoke with my father who is an electrical engineer, and he believes that the reading on the ground side is likely some residual voltage and not the problem.

I too noticed that the universal I recieved didn't look like the factory sensor. Oddly enough, I had the o2 sensors out of a 96 Maxima just yesterday and they looked identical to the Subaru OEM sensor.

Regardless, UPS indicates my Denso OEM replacement will be here tommorow. Then it will be a fight to get PepBoys to take back the bad sensors.

[BAC5.2]

Ground should be ground. A ground that sees voltage is not so much of a ground now, is it?

I guess I'll go pop the hood and test and report my findings with a working front oxygen sensor.

I'll post up in a few minutes.

[BAC5.2]

Just tested out my Forester.

The Forester has 2 types of Oxygen Sensors. The rear is a 4 wire, the front a 3 wire.

I tested both, key on car off, and key on car on but with the sensor unplugged because I'm lazy.

Here's what I found.

Heater = 12.1 volts
Ground = zero volts
Signal = zero volts (car is off, key is on, there should only be a signal if the O2 sensor is reading something).

to further verify my claims, a 4 wire oxygen sensor has the following terminals. Signal wire, Ground, Heater hot, and Heater ground. At the connector, with the connector unplugged, the heater should read 12 volts, and everything else should read zero. There is no signal so that = zero, and both other wires are ground wires.

It appears that you have a bad ground. I would be quite sure that if you re-grounded the ground wires (with the correct sensor, of course) your problems would cease to exist. But first, I would check all extensions and recheck the wiring. Start at the ECU and check resistance and continuity on the wires.

If you have a corroded wire or connector, then you will see continuity on more than one wire for a given matching wire (i.e. ground and signal will share continuity with ground at the connector).

I don't think residual voltage is the cause for this, and espically can't count for 3.8 volts! It didn't show any residual voltage in my car. I think ground read .1v, which is well within the specs allowed for residual voltage.

That's my .02.

[jmgtp]

Thanks for doing some research on this.

I'm still banking on a bad o2 sensor and not wiring.

Heres why:
The P1133 indicates a faulty heater element. The OEM sensor that I removed does not have continuity across the heater element, hence it is definetly bad.

The replacement univesal sensor trips the SES instantly, swapping the rear OEM sensor to the front trips the SES after 10 seconds or so.

Wiring all looks perfect from what I can.

None of this rules out a bad ground, but my father (the electrical engineer) seems to think the small voltage is negligible - for reason of course that I cannot explain so you can throw this theory out if you like.

We will know tommorow when the replacement Denso is installed, so long as UPS delivers on time.

Thanks,
John

[BAC5.2]

But you said yourself (and I confirmed) P1133 isn't necessarily a faulty heater element in the oxygen sensor.

P1133 is a high input for the heater circuit.

That could be lots of things.

I DO know that you should have zero voltage at ground and on the other two wires. The only hot wire should be the heater feed wire. The fact that you have a voltage on the other wires shows that something is wrong. 3.7 volts is a lot of volts in a 12 volt system. Unless you are measuring it wrong, it sounds like there is a short somewhere in the system. The signal wire and both ground wires aren't connected to anything but the chassis and the ECU. Neither place produces an output signal.

What scares me, is that when you plug in a good oxygen sensor, you will have an altered signal from the sensor because of the faulty wiring. It may not show as a code, because it is consistent and there really aren't any other factors the ECU can reference other than MAF signal. If the sensor reads hot (lean) the upset wiring will bump the output voltage a few volts, making the ECU think it's running richer than it should be. Luckily, AFR in a stock NA car don't vary TOO wildly, so the car running a little lean isn't necessarily a bad thing. But if a working sensor puts things perfectly in spec, the ECU might cut fuel to drop the O2 sensor voltage, causing a lean condition. The ECU would recieve a normal signal from the 02 sensor but the actual condition of the engine would be lean. Lean = det. Det = blowedness of the motor.

Has the car been getting unusually good or poor gas mileage?

It set the code twice because that's the ECU standard for setting a code. This particular event must take place at least two consecutive times in order to trip a DTC.

The universal sensor should have not allowed the car to run, rather than just throwing a heater element code. The car would have run and idled rich as shit with the incorrect universal sensor.

While the heater element might be bad, I think you might have a few more problems than just that.

Remember, I JUST tested it on my car, and the only hot wire was the heater 12v. The others were zero, and my car hasn't set a check engine light. I think you should be less concerned with a heater element that is bad, and more concerned with WHY it went bad. 50,000 miles is well within the useable life of an oxygen sensor (espically on an NA). Both sensors in my car have three times that mileage with no issues.

Just my two cents. I would hate for you to lose the $100 you spent on a new sensor when the car eats it alive because of faulty wiring.

[jmgtp]

Well, I had to ask my father again since I really didn't understand how/why there was voltage on the other wires when there should not have been.

The reason he gave is simple. I used his digital multimeter to take the readings. It has a button in the center to 'zero' the meter. If zero'd the voltages would have been negligible. I recall the very same issue on my Grand Prix when the fan relay failed. The meter measured 12v between the ground wire on the relay and the engine block! Sure enough, zero out the meter and the voltage was measured was under .2 VDC. Popped a new relay in and haven't had a problem since.

Given that, and the open circuit on the original o2 sensor heater element I think it is fairly safe to say the issue lies with the sensor itself. I fail to see where the wiring could have gone bad other than the ECM itself. When the new sensor goes in tommorow (hopefully!) if the light is still on then it'll be time to dig deeper.

[BAC5.2]

Ahh, information that would have been useful to know. I was assuming you were using the multimeter correctly. User error would definately cause discrepency. So yes, the sensor is absolutely to blame for your problems.

If you DID have a 3.7 volt residual voltage in a ground or signal wire, I'd be very scared.

Usually you zero a multimeter on a known hot source. It's force of habit for me to check my multimeter performance by first testing my battery voltage. If the car is off, I can expect just above 12vdc. Car on, just around 14vdc. If it's different, I start diagnosing wtf is wrong with my multimeter.

[jmgtp]

Denso sensor installed, CEL light gone!

Now to convince PepBoys to take back the bum bosch universal they sold me!

[caplem]

what was the part number of the o2 sensor that you used I am having the same problem only my car has a 2 wire sensor

[jmgtp]

what was the part number of the o2 sensor that you used I am having the same problem only my car has a 2 wire sensor

Thread from the dead! Nearly 4 years old. I sold my Legacy over a year ago. But... I have an answer for you!

The sensor I picked up was a Denso #234-9018. It was a plug and play (correct connector).
I purchased it from sparkplugs.com and at the time it was $107.95 shipped.
Looks like my keeping track of all the maintenance and receipts in a spreadsheet came in handy!

hope this helps ya out.

Good to see the forum still kicking! Sure does look different than I remember though.
And in case you were wondering, yes, I do miss my AWD LegGT. Just thinking of it makes me a bit sad its gone. I do have problems letting go of cars though... I have 3 cars right now and I really only want to have 2 but I just can't part with them, I get too attached.

-John