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ECU or Cat or what?


vjm
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Hi I have a 2002 Rav 4nrg (petrol) automatic. About 2 years ago the engine warning light came on but the garage said the diagnostics didn't show anything so to ignore it. It has come on very occasionally since then, with no noticeable drop in performance. However, starting about 6 months ago, the car sometimes took longer to change through the lower gears and 2 or 3 times has made a loud clunking noise when pulling away. On long motorway journeys it goes like a bird and is fine. It seems to be when I have been in slow moving traffic or when it is ' pushed' up a steeper gradient. I have learnt to pull away slowly and nurse it through the gears which is usually fine. I took it for a diagnosis because having read on here about ECU problems, all the descriptions seemed to match mine. The only codes thrown up were P0420 and P0430, catalyst efficiency system and PO500,vehicle speed sensor A. My mechanic didn't suggest the cat and clearly thought it was not the ECU because of the codes and intimated that I should just 'see how it went' and if it kept happening, just get rid of it, i.e., he couldn't really be bothered or he was thinking about my purse! If it was the auto gearbox, would that have thrown up a code? I love this car and don't want to lose it even though it's old now (mileage 125K) but is in great condition body wise. I have read on various sites, not to immediately change the cat in the first instance, because it could be a variety of other faults which are just affecting the cat. I need to know that if I go along the repair route, a rough idea of cost, as my budget is limited. I would love someone to give me an explanation if possible of potential causes of this and remedies if they have experienced the same problems. Hoping for uplifting responses!!  Thanks so much, Damsel in distress!

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I can’t help much on the issues with the auto gearbox ( but suspect that the speed sensor issue could be related ) but the eml light and dtc P0420 could very well be the second lambda sensor. This is located downstream of the catalytic converter ( approximately underneath the drivers footwell with the wires coming through the floor and into a connector on the right hand side of the centre console adjacent to where your left foot would be resting when driving ) 

We had the very same DTC on our 2004 2.0 vvti Rav 4, the eml light would come on very 50/150 miles and after changing the lambda sensor ( for a genuine denso sensor, don’t be tempted by a cheap aftermarket copy )  and clearing the code it has not reappeared in over 1200 miles. You can get a new denso lambda sensor with electrical connector for circa £80 or a denso lambda sensor with approximately 700 mm of cabling ( and just crimp onto your existing electrical plug ) for circa £38. I went for the second option and It took around 30 minuets to fit.

Hope that is of some help.

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You've possibly got two or three different problems. The auto gearbox problem is probably the dreaded ECU fault and it is possible to get the unit tested and repaired.  It's not a good idea to put up with the fault since gearbox damage can be the result. P0500 is a speed sensor fault and can be the sensor itself or a connector problem. In the first instance - delete the fault codes and check to see if it re-appears and that it wasn't just a transient fault. P0420 and 0430, on the face of it result from poor catalyst efficiency - it is not a lambda sensor fault. Your model has 4 sensors unlike the previous posters Rav which has two sensors. This fault code won't result in a performance or economy issue. The ECU has a testing regime which compares the output of the pre and post lambda sensors and if it spots a change - it flags up the codes. It usually happens on this model when there's a significant mileage on the clock and there is, understandably, a build up within the catalyst. Often, all is well on short journeys then the codes are thrown up when the car is driven enthusiastically on the motorway. All that's happened is that some of the buildup has been expelled - the ECU sees a change in lambda output comparison and throws up the codes. It's not solved by changing any of the sensors. Sometimes it's possible to keep the problem at bay with an enthusiastic drive once / week but in other cases, the only permanent solution is to replace the cat. There are many owners who simply ignore the fault codes - it's not an MOT failure and there isn't actually an emissions issue. 

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And in terms of cost -

ECU repair + remove / install - £350. There are several outfits that will repair the ECU but this company in Derby is recommended by many

http://www.ecutesting.com/catalogue/toyota_eculist.html?category=4051&model=626

Cat replacement - £400

Speed sensor - probably 30 mins labour to check and clean connections at the sensor and the plug in connector behind drivers side kick panel. 

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Thank you so much for those responses Flatfour and gjnorthall- very helpful indeed. Maybe I can sort this problem once and for all just short of £1000 then? Would you agree that it's worth spending that amount on this car, which as I said before, I really like and would like to preserve, or would you say I might be throwing good money after bad? I do appreciate that's a hard one to answer when you don't know the car, but if you were me...........??

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Hi,

It might just be worth taking the car to a Toyota dealer and paying for a diagnostic check, believe they charge for a half or a full hours work; get a quote first.

You may get a better idea of whats wrong  ...

Have no experience of auto boxes, but from watching tv programs like Wheeler Dealers, having correct oil changes and filters in the auto box is essential as they can cure many weird problems;  a guy even sold his Porsche for £1k because of faults  he thought it needed  many thousands to cure,  yet  a simple filter and oil change cleared it up.

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My inclination would be to fully check out the speed sensor fault first (you don't mention if the speedo gives an erratic reading or doesn't respond for periods - this is an usual symptom of a speed sensor fault). It's probably low cost and a faulty sensor can cause auto gearbox problems so it's worth eliminating this possibility (the gearbox  ECU needs the vehicle speed to compute the optimum time to change gear). Then get the gearbox ECU checked. The outfit I recommended will check the unit and if no fault is found - they'll charge a modest fee for testing. If the unit is found to be faulty - then it's £200 + VAT to fix. It's a very common problem on the 4.2 Rav auto and the fix usually solves the problem completely and permanently. The only unease in your case is that the car has been driven for a fair time with a likely faulty gearbox ECU and this can result in gearbox damage - so there is some risk - but your description would suggest the box is OK so fingers crossed!. If the rest of the car is good - then a spend of around £400 on a car you know and love is not too bad. The catalyst fault is more of a quirk of the monitoring system rather than a failure (performance, economy and emissions are not affected ) and I'd be tempted at this stage not to spend any more on the car and live with the issue. It may be that an "Italian tune-up" every so often will keep the fault codes from appearing. 

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Thanks very much.  Speed sensor will be my first job then. As you say, I really hope the gearbox hasn't become damaged. I will re-post once I've had repairs done as this might be helpful for others who are experiencing the same problems. :smile:

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Vjm, totally agree with gjnorthall's views, about the gearbox, had your exact problems 2 years ago and was in panic mode thinking I needed a re-placement gearbox, (love my Rav), found out about Ecutesting in Derby from here on the forum, removed and sent off for repair, easy done as its behind the glovebox, back in less than a week and going like a Swiss watch ever since, complete with 2 year warranty, would be very easy for your local mechanic if your not happy doing it yourself, it is secured ( the ECU) by oddball Torx screws, the forum suggested I get the Torx bits from Amazon, BTW the 2002 model RAV4 Auto is renowned for its ECU going faulty.

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Thanks Gower boy, that has made me feel hugely optimistic! I have given my mechanic all gjnorthall's  notes off the forum (the mechanic probably thinks I'm a pain, but I think it's all really helpful stuff and tbh he hasn't come up with anything!) and I will take yours to the garage tmrw for him to read.

So a couple of days ago we had a horrible time going through town, lots of stopping and starting and for the very 1st time the Rav really struggled in low gear - didn't think I would get home. I too thought the gearbox had had it. So took it straight to the garage and today he has tested the speed sensors and found nothing wrong. So I have asked him to remove and send off the ECU- he moaned about how hopeless the company were!! I know...….after this job I'm going to use another garage! :unsure: But your remark re 2002 auto Ravs makes me think we might just get this right - really hope so cos I love my Rav too.:smile: Thanks again everyone for all this advice- very much appreciated.

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  • 2 weeks later...

So an update for anyone who is experiencing the same problems.

I followed advice on here to the letter and had the speed sensor checked out first - no problems came up with that. So, even though my mechanic seemed reluctant to look at the ECU problem because of the age of the car, he duly sent it off and  it arrived back today. (Apparently it only took 10 minutes to fix!)  Once he'd fitted the ECU and came to start the engine, the Battery was totally flat -any ideas why, as it's a virtually new Battery?   Anyway, jump leads later, I took it on the test run with my heart in my mouth just waiting for the clunk and the stuttering, but absolutely nothing happened. It went so well and I drove round for an hour so that it could gently sort itself out again.  I'm keeping my fingers crossed, encouraged by Gower Boys post and full of gratitude to gjnorthall for his brilliant analysis of the problem. Thankyou so much - this forum is priceless. 🙂  🙂

 

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One possibility re the flat Battery - the alternator is defective.  Check terminal volts when stopped and when engine is idling.  A good alternator should be putting out around 14V, whereas the Battery alone should be upwards of 12.5V.

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The OP indicates that the Battery has gone flat whilst the ECU was away for repair and as such the alternator hasn’t been called upon to charge the Battery. it may be something silly such as leaving the interior light on whilst awaiting return of the ECU. Presumably after running the car, the Battery has charged up - just check that the battery appears to keep its charge over the next couple of weeks.

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That assumes the Battery was topped up before the ECU was removed.  If the alternator has been limping along for some time, the few days waiting for the return of the ECU may have simply been the last straw.

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