Engine Malfunction Indicator...

[-Matt-]

Hi all, this is my first post here so please be nice!

My girlfiends RAV4 (2001 NRG ~73K miles on the clock) has the engine malfunction light illuminated.

About a year ago the light came on and she called out the RAC. The RAC guy said that the fault code was caused by the oxygen sensor. He reset the fault code and it didn't come back until just before Christmas...

Just before Christmas the light came back on. My GF's independent mechanic read the codes again and replaced the oxygen sensor at a cost of £230, (£160 was for the part). A few miles after getting home the engine fault light came back on again.

If I disconnect the Battery for a while then re-connect this will clear the engine fault light, however, the light comes back on after about 10 miles.

How can I check if the mechanic replaced the correct sensor? Could there be an intermittent fault with the wiring perhaps?

I am thinking of getting a code reader to look into problems like this.

Obviously we don't want to spend £160 on each of the four sensors if there is a common problem with water getting into the wiring or something.

Any advice would be gratefully recieved.

[Jamesbelfast]

There may be nothing wrong with the sensors. Over-fuelling or a misfire will cause the engine managment light to illuminate. Time to find a decent garage me thinks - one who knows how to diagnose problems correctly and not try and fix things by substitition entirely at your expense.:)

[rambler]

hi matt

firstly,welcome to the club :D

im not sure if it applies to both fuel types?..you say 2.0....petrol or diesel please?

anchorman should be able to help you.....top bloke here as far as im concerned

but others may have other info for you

cheers

rambler

[-Matt-]

Thanks for the replies

Sorry I should have said, it is the 2.0L petrol.

[anchorman]

Welcome to the club Matt.

Your problem isn't uncommon and these sensors can be a bar steward to sort out. There is every chance that your garage changed the correct sensor but there are 4 typically and any one could be playing you up. Garages with high end diagnostic equipment might help you out or a main dealer but keep in mind that even the best equipment doesn't always give a clear answer and you might end up changing them all before you bottom it.

Good luck and keep in touch.

[Puma]

Welcome to the club Matt.

Your problem isn't uncommon and these sensors can be a bar steward to sort out. There is every chance that your garage changed the correct sensor but there are 4 typically and any one could be playing you up. Garages with high end diagnostic equipment might help you out or a main dealer but keep in mind that even the best equipment doesn't always give a clear answer and you might end up changing them all before you bottom it.

Good luck and keep in touch.

Best bet is to check all of the sensors for resistance with a multimeter. If you have a "Sparky" mate he/she will be able to do it as it will stick out like a sore thumb.

[-Matt-]

Here is an update...

My girlfriend took her rav4 to another mechanic (an independent Toyota specialist this time). After paying for a "full diagnostic check" this mechanic said that the reason that the sensor failed immediately was because it wasn't a genuine Toyota part. They recommended changing the it out for a genuine part.

With this information we returned to the first mechanic who swapped the part FOC. (He was going to claim back the cost of the first replacement part from the supplier).

During the test drive immediately after fitting the new (geniune) part, the EMI light came back on.

The mechanic is now suggesting sending the ECU off for testing. I would have thought that if there was a problem with the ECU it would just stop working altogether rather than just throwing a lambda sensor fault code.

I think that the most likely cause is some faulty wiring somewhere between the sensor and the ECU. This would account for the fact that the fault was intermittent at first. Of course nobody wants to have to check through this wiring because it is a pain to get to. I suspect that is why the mechanics keep suggesting the easy fixes.

My girlfriend is getting really upset over this and can't afford to keep throwing money at the problem.

...And so I arrive at my questions: I have a multimeter and have done a fair amount of soldering etc. What testing can I do myself?

Where is the ECU located and which connector pins correspond to the lambda sensors?

What route does the wiring from the sensor to the ECU take?

What voltage / resistance should a known good sensor produce?

[mrbilly]

what you could do if find out if your rave has rear lsd and swap it with mine for 150 pounds then buy another sensor

[hedleyf]

HI,

Not worth going in there with your multimeter the signals being put out from the sensor are jargon untill the logic in the ECM sorts it out to be read by the Toyota tester, P.C

I would recommend to take it to a Toyota main dealer, in a 20-30 min while you wait check they should be able to fully fill you in on whats wrong, the system has two O2 sensors and two A/F sensors,

on the P.C with the engine running they can monitor signals from all sensors at once and see the problem straight away, 9 times out of 10 its one of the A/F [ air to fuel ratio ] sensors that have gone down, normally because the electric heater circuit has gone open circuit. codes will pin point the exact position of that sensor this is where some mechanics get mixed up and change the wrong one,This should be simple ,main dealer while you wait check the fault, 160 for a new sensor, and 30 to 45 mins to fit it .

[Andyf3854]

Please don't say it could be the ECU, we have just traded my wife's Astra in for a Rav4 and the same light was on on the test drive. They said it was the lamda sensor and we are currently waiting for the part. The old Astra had a similar problem that a garage said was one sensor then another so after £250 we get told it needs a new ECU, the car ran fine although the cruise control stopped working so we got rid of it for the Rav4 which seems to have one problem after the next that garage can't sort out, this light had better not be one of them!

[-Matt-]

@hedleyf

So is the signal from the sensor digital pulses rather than just a dc voltage level?

I am concerned that taking the car to a main dealer for diagnostics may not solve the problem...

When you plug in for diagnostics all you are doing is talking to the ECU. The car has already been plugged into two different diagnostics computers. The ECU consistenly reports a fault on the same sensor. The sensor has been replaced twice but this doesn't seem to have fixed the problem.

My theory is that the ECU is correctly reporting a fault because it does not get a proper signal from the sensor. However there is obviously nothing wrong with the sensor since this has been replaced. The conclusion must be that there is a problem with the wiring between the sensor and the ECU. Unfortunately they don't seem to test the wiring when they do "Full Diagnostics".

[anchorman]

This gives some info on operation and testing. I sometimes wonder if a secondary fault is affecting the way the sensor is behaving and thus causes it to give out the wrong info.

Technical articles/OBD II/oxy sensors

http://www.autoshop101.com/

[-Matt-]

That looks like a great site, thanks anchorman.

[rpaterson]

Did your mechanic tell you what the actual fault with the sensor was? Two of the sensors have a heating circuit and this is a known weak spot. My wife's engine light is lit due to a dodgy heater circuit and I'm very close to just splicing into the 'good' circuit to put the light out.

[hedleyf]

Hi,

You need to find out what the problem is , its ok saying the sensors at fault but whats wrong with it ? its going to be one of a few things, two possible codes are, 02 signal fault or 02 heater circuit fault, there are verious other codes onto each of these two main codes ie signal to low ,short to earth,short to live, etc ,etc. lots of diagnostics will tell you that the sensor is faulty but no further info, Toyota diagnotics can go further by using other codes within the main code, Anyway knowing Rav 4s I would think its a heater circuit gone down,if you know the sensor you can check its continuity by removing the connector plug ,inside you have four pin terminals two colored gold,and two silver ,the two silver ones are the heater circuit wires, using your multimeter connect to the silver wires and select ohms on the meter, you are looking for continuity through these wires, if the meter remains in open circuit this means the sensors U/S. it will need changing, if this is ok its still possible that the heater circuit is not working, this is powered Battery voltage that is switched on and off as required by the ECM, via a relay, you can also check the resistance through the gold wires {signal} I think off the top of my head its about 11 to 14 ohms on a good one,this is at normal ambient temp, Don't go changing the ECM as I have never changed one in ten years,they are normally very good, I suspect your problem lies else where , the voltage output from the sensor is a A/C voltage of about .1 to .9 volt, it is very hard to measure with a multimeter because the reaction time on it is to slow, you be better off with a dial meter but what your looking for is the pattern and not necessary voltage, this takes practice and experience to know what looks right.

Hope this helps, good luck.

[jako999]

Hi my wife has a 2002 and we have the same problem on ours ongoing now for 3 months I have a fault reader with live data it said heater gone I meetered it out and yes it had so I replaced it. You can get a denso one from Euro parts for £84 and denso make them for Toyota. I put it in and all looked fine for the fist few miles then it came back on but then we had 3 new fault codes we ran it for a bit to see if it cleared which it didnt but the funny thing is the mpg dropped by 2 and as it only does 18 in town thats quite a lot. I changed it back for the old one and the mpg is fine again the replacment part has now gone of to be tested but the funny thing is I had the emitions checked and there fine? I have also replaced the plugs and air filter just in case as they are cheap and looked for air leaks.

It realy is starting to do my head in.

After speaking to Toyota they seam to have no idea but they did say its common and would cost a fair amount to fix!!

After a lot of searching what I have found is that a lot of the cars in the US have the same problem and there is a fault with the computer that only shows with age and over there its fixed by a free of charge remap. When I get the lambda back from test If the fault is still there then this is something I am going to look into.

Please stay in touch and who evere gest the answer first can help the other.

Thanks

[anchorman]

I read both of these codes recently on a VVTi UK RAV;

TSB_oxy_sensor.pdf

Maybe your Toyota Centre can get access to this ECU flash?

[rpaterson]

An interesting read Don. My fault is defo the heater circuit, although I've not multi-metered it yet. Would I be correct in thinking that this bulletin wouldn't do anything for me?

[anchorman]

Well put it this way, I wouldn't write it off. Just have a look throught the pdf in post 12 above. If the heater circuits prove OK then it might be worth a try.

[R2 D2]

I read both of these codes recently on a VVTi UK RAV;

TSB_oxy_sensor.pdf

Maybe your Toyota Centre can get access to this ECU flash?

Hi all, first post, hope this is useful....

I have the EMI problem, bought my 2001 3Dr NRG VVti 2.0 petrol Christmas eve 09 , then noticed the temp guage sticking, so pulled the inst. cluster apart and found that the needle was catching on the dial face because it was slightly raised, after lifting the dial facia I found that some nice person had covered the EMI light with a black rubber cap. So after removing said foreign object and re-assembley I have a working temp guage, but have also revealed a constantly lit EMI ! Anyway, sorry for rambling on, Whilst searching the internet for possible causes, I found this document, might be helpful.

I hav'nt done anything about the EMI problem yet, still considering buying a code reader etc, my rav was last serviced by Mr T 2004 so not sure if this work has been carried out yet. EG5010_0_1_RAV42_DTC_Oxisensor_Kat.pdf

[john21245]

Well put it this way, I wouldn't write it off. Just have a look throught the pdf in post 12 above. If the heater circuits prove OK then it might be worth a try.

What we must remember is that codes are only guides to help trace malfunctions. Too many so called mechanics are just fitters who bolt anything on without investigating faults thoroughly.On one of our toyota,s an illuminated engine management light which tested ok was indicating a failing cat which wasn't doing it's job effectively.I'm not implying that this is relevant here but we sometimes need a bit of lateral thinking.

John.

[RichT-XT3]

I read both of these codes recently on a VVTi UK RAV;

TSB_oxy_sensor.pdf

Maybe your Toyota Centre can get access to this ECU flash?

I have this fault., but over 80k so out of warranty. should I just live with it, or will my 32 mpg be a result of it

Regards

RichT

[Big Kev]

I read both of these codes recently on a VVTi UK RAV;

TSB_oxy_sensor.pdf

Maybe your Toyota Centre can get access to this ECU flash?

I have this fault., but over 80k so out of warranty. should I just live with it, or will my 32 mpg be a result of it

Regards

RichT

32mpg from a petrol Rav is totally (sometimes better than) the absoute norm.

Big Kev