02 sensor issue

[Mollydog]

Getting my MR2 back on the road last week from an 18 month off road, I had to use an OBDII reader to wipe the error code off from the MIL light on the dash to get it through the MOT

The OBDII reader shows that there is an O2 sensor issue, error code P0030 (I gather this is an error code for the heater of the 02 sensor),

looking at the screenshot of the OBDII reader it looks like two of the three sensors are playing up

Seeing how much each 02 sensor costs, I thought I'd post on here for any help before I fork out for them, here are the readouts, if any issues are spotted I'd be grateful for any help


The two part for the 02 sensor





These are the rest of the readouts



























I have replaced the over 2 year old air filter and plan on cleaning the 02 sensors and use a multimeter on them to see if it shows any resistance from heater wires, I bought a can of carb cleaner and a small bottle of injector cleaner to use on them.  I took out the MAP sensor and gave it a good squirt of carb cleaner but that didn't do anything

Many thanks

[Gaz mr-s]

A maf can be faulty but doesn't produce codes.  Both displays say Bank 1 sensor 1, which is one on the right side as you look at it. Don't waste your time cleaning it. You can disconnect Bank2/1 & measure it (should be ok), but don't remove the sensor. It often damages them internally doing so.
There is a bodge of wiring a resistor across the heater cct wires so that the ecu sees a circuit. Google it.

[Dev]

 Using a multimeter to test the heater circuit is a good move. If the heater is burnt out it just needs a new 02 sensor and you are done. You should never clean 02 sensors as it can damage them.

[paulj]

Its one sensor you need. The current code shows a fault and the pending code shows a fault which hasn't yet triggered the engine light. As mentioned there is a bodge for the heater circuit but I would suggest a new sensor. Once replaced it is one less thing to think of!

[Mollydog]

just placed an order for an 02 sensor, should be here by Thursday, I'll still check for resistance with a multimeter just to find out

[Mollydog]

I put the multimeter to the two top 02 sensors,. the one on the right (driver side) there was neither continuity or any resistance

Continuity


Resistance


the one on the left (passenger side) there was both continuity and resistance

Continuity


Resistance


I didn't get under the car to test the third one

As mentioned I ordered one 02 sensor that should arrive by this Thursday hopefully it will solve the issue or I'll be need to get in there and checking fuses and wiring (I hope not)

On a side note, we've had (it's my wife's car) the MR2 since November/December 2006, when we bought the car it was around 17/18 months old so we weren't the original owners, in all this time I've only this morning noticed that the wires going to the MAP sensor look as if they have been tied up and not anchored to a point on the car with the connector attached to the wiring







Or is it a case of these sensors are made to be used on other Toyota cars as well and as such the fixing point is not needed on the MR2?

[Joesson]

@Mollydog
That fixing "point" should connect into a "socket" on the vertical face of the air filter housing adjacent to where it's now "hovering".
I would guess it meant that at some time it was disconnected to open the filter housing and, hopefully, replace the filter.

[Mollydog]

@Joesson

thank you, I'll go and take a look now

Edited to add:

I found it and fixed the issue, not that I have OCD but like to know it's fixed safely





I saw that protruding on the air filter box when I changed the air filter the other day, I didn't know what it was for though,

I bet at one time or another a mechanic, when doing the service on the car thought it wasn't the right place for the fixing, I have to agree I don't think its the right location for the fixing point as every time the filter gets changed you have to faff about the fixing


Now I do my own service on the MR2, next time I change the air filter I might do what the mechanic did and tie it up off the air filter box

[Dev]

 The two black wires on the 02 sensor wiring is for the heater circuit. If it is open then the heater is blown. This is a good sign that no other diagnosis is necessary and it just needs a new 02 sensor.

[Mollydog]

Thank you Dev, yes looks like the driver side one had blown, hopefully the bottom one is OK, if not another one will have to be fitted there too

[Gaz mr-s]

Thank you Dev, yes looks like the driver side one had blown, hopefully the bottom one is OK, if not another one will have to be fitted there too

Each sensor has a different code to identify them.

[Ardent]

I didn't get under the car to test the third one

You don't need to. The lead runs up to and behind the left rear light.

Might of need to remove the light.

[Mollydog]

Thank you Ardent, not having a workshop manual I was guessing I had to get to it from underneath, in this case I'll attempt to get to the lead of the third 02 sensor tomorrow

@Gaz mr-s

thank you for this information, in this case I'm hoping all is well with the bottom 02 sensor

[Dev]

As Gaz pointed out you don't have to go though the trouble of testing the third 02 sensor for the Cat.
 If the heater circuit blows you will get a code. If there is no code you its fine and that 02 sensor is not part of the fueling loop. It just tells you that the cat is ok.

[Mollydog]

I was surprised to say the least to see that my O2 sensor had arrived this morning as I only ordered it Sunday night and wasn't supposed to be here before this Thursday



I didn't waste  a minute getting the 22mm 02 sensor socket out to the car





This is/was the condition of the old (maybe original) 02 sensor





This is the new one (not Toyota original)



I torqued the 02 sensor to 44Nm





All tools put away and start the car, low and be hold



I got out the OBDII reader and showed PO135, bank one sensor one was still an issue,



but this time also showing that there is an issue with bank one sensor two PO141



I checked if there was any power to bank 1 sensor 1 and tested the two power wires for voltage and the meter showed 3.5v



I cleared the error code and took the MR2 for a drive on the A1 (M1) near me that's around 20 miles long



Around a mile or so before the road turns back in to an A road the MIL light comes on,  once on the A road I pull over and get out the OBDII reader to check what error codes it was going to throw up

This time all that showed up was the error code PO141, no PO135 code showing



I cleared the code and drove back home sure enough around a mile from home the MIL on the dash comes on, I get out the OBDII reader and it shows only error PO141 no PO135 code



I put my multimeter on the heater wires on the bank 1 sensor 1 02 sensor and the meter shows a resistance of 14.6 with engine at running temperature



thought I'd see what the continuity was, it was 14.4




It's getting dark outside now so in the morning I'll be putting the multimeter to the post CAT 02 sensor and see what shows up

This is a bit of a mystery really

[ManInDandism]

Fun and games eh   Not the first MR2 owner and won't be the last to be having this sort of issue.  I spent a year trying to get to the bottom of a P0136 - new O2 sensors, studying the pages in the diagnostics section of the repair manual (lots of stuff there), MAF clean, checking voltages across the wires with a multimeter, viewing nerdy O2-specific videos on YouTube, analysing the output from an ODBII data logger etc. It only finally went away when I replaced the cat which was a Malian rather than OE and was blowing ever so slightly.

Hopefully this won't be the case for you, but seems you are taking all the logical steps.  Not sure what make of sensor you have purchased, but it is documented to not cut corners here and to use something that is Denso quality (I believe Toyota ones do break the bank).  The other thing I picked up is that the Bank 1 sensors effectively work in unison and ECU not always clever enough to know if fault was with one or the other so just throws the nearest code. So apparently when you took a car in to Toyota to diagnose back in the day, they tended to change both of the sensors on that side.

Not really sure what to suggest since if just changing the sensor itself does not resolve it, seems it can turn into a bit of an epic but best of luck.

[Mollydog]

I bought a cheap one off eBay if this gives up the ghost then I'll cut my losses and buy the Denso one,

I checked the downstream sensor yesterday and as expected no resistance or continuity so placed another order for an 02 sensor, hoping this will sort out the issues, in passing apart from a longer cable is there a difference between the upstream and downstream 02 sensors?

[shnazzle]

Sensors - Denso only, or expect failure. DOX-0204 and DOX-0206 for the one in the cat. Alternatively DOX-0109 if you don't mind crimping a few wires.

[Carolyn]

I bought a cheap one off eBay if this gives up the ghost then I'll cut my losses and buy the Denso one,

I checked the downstream sensor yesterday and as expected no resistance or continuity so placed another order for an 02 sensor, hoping this will sort out the issues, in passing apart from a longer cable is there a difference between the upstream and downstream 02 sensors?

No difference.  Treat them very gently.

[Mollydog]

I bought a cheap one off eBay if this gives up the ghost then I'll cut my losses and buy the Denso one,

I checked the downstream sensor yesterday and as expected no resistance or continuity so placed another order for an 02 sensor, hoping this will sort out the issues, in passing apart from a longer cable is there a difference between the upstream and downstream 02 sensors?

No difference.  Treat them very gently.

thank you, the pain of getting to the downstreem one, I'll be using woolen gloves

[Gaz mr-s]

Be aware that they can be stuck with rust. One of mine wouldn't come off on a garage ramp & a big breaker bar on it. I did the resistor bodge.

Seized-on is not uncommon, garage said sometimes the pipe cracks before the sensor does.

[Carolyn]

The post cat sensor can be a bugger to get out, as Gaz says.

If it won't budge, I take an angle grinder to it and cut it down to the hexagon, then get it good and hot with a plumber's torch, then a six point socket and a breaker bar.

I've done a few, and that has always done the trick.

[Mollydog]

As I was changing the oil I had the car on ramps, I made a start on the 02 sensor, circuit bank 1 sensor 2, the one past the catalytic  converter

Seeing how hard it was getting the 02 sensor wire off I couldn't see myself using the same fixing points Toyota used for the 02 sensor wire,

I found it difficult taking the rear lights off as I have that duck tail so I took out the  header tank and this gave me room to move around behind the lights and connect the 02 plugs together

I have a lot of this wire shield conduit I use on my cars when doing electrical mods



So to protect the wiring from chafing I cut a length of it to cover the full length of the 02 sensor wire







I used a 3/8 breaker bar and to my surprise with little effort the 02 sensor moved and I ended up unscrewing it with my fingers





Fitting the new sensor was a bit fiddly as it wasn't easy catching the thread and a few attempts were made before I got a small bite then used the 02 sensor socket to hand tighten before I used the breaker bar on it, NOT over tightened just a bit more than hand tight



Then came the threading of the new cable, I attached a stiff wire to one end of the 02 sensor wire and threaded this through to below the header tank location



Pushing up



Pulling up



I used a few cable ties to hold down the wiring





I also used cable ties near the 02 sensor but forgot to take any images, I drove the car around our ring road a couple of times (around 10 mile trip) and the OBDII reader showed no error codes,



let's hope this is the case when I check it tomorrow if so then I'll torque it up

[Chilli Girl]

Excellent write up and pics, very well done.