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Toyota Avensis 1.8 1999 - Poor Lambda behavior #

Posted by Paul Howd on August 31, 2012, 7:57 pm

Year of Manufacture *: 1999
Engine Size and Code *: 1.8 7A-FE
( Optional ) Scanner Used: Multiscan
( Optional) Fault Codes: None

This might take a while but....!

Failed MOT on emissions CAT is clearly not working correctly BUT!

Customer has had new CAT (But no new lambda sensor) for each MOT for the last three years. (And a new one now would likly squeek it through) The CAT failure is the symptom not the cause I suspect.

Lambda switching was slow and when warm fixed at 0.45 volts at idle. At speed lambda does switch but not very well and only switches between 0.45 and 0.8v.

It only switches down to 0.2 at the point that the throttle is snapped open from idle, after that it resumes switching between 0.45 and 0.8

There is a "Live Data" line that says (something like) "O2 sensor lean signal 0.45v" (Unfortunatly I didnt write it down precisly)

The earths at the lambda sensor appear good (The switched earth for the heater bottoms out at about 0.5V but one would expect that for a semiconductor switch)

there is no apparant false signal on the ECU side of the lambda sensor with the sensor disconnected.

Thinking that, On a 200,000 mile car, the lamda sensor was still the one it came out of the factory with and that the misbehaviour might be consistamnt with a combination of age and possibly an internal voltage leakage I replaced the sensor.

Its still the same! (But then I did warn the owner that this was as much a "diagnostic" replacement as a fix one)

He is understandably reluctant to spend too much on the car, but at the same time he really likes it and does not really want to replace it. Appart from the MOT fail this car really does work really well!

Oh, another bit of data, the fuel trims are both essentially unmodified, both long term asnd short term.

Any suggestions?

Paul

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by aidan birley on August 31, 2012, 8:10 pm, in reply to "Toyota Avensis 1.8 1999 poor Lambda behaviour"
Aidan Birley

paul

can you please post all 5 emissions readings at idle and cruse.

Cheap after market,(even more so non type approved) cats will typically last less than 1 year.

Engine mechanical condition needs to be confirmed good.

does the scan tool indicate if it is running open / closed loop ?

do measured voltages agree with live data?

cheers Aidan

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by Paul Howd on August 31, 2012, 8:41 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
Paul Howd

Thanks for quick response, However.

I really do not believe that this is primerily a CAT problem. Though the cat is not working properly I suspect that it (they) are being killed by a fueling issue.

The lambda is not switching properly (Very slow sine wave like signal on the scope)and is exhibiting this rather strange 0.45V floor issue.

The (calculated) lambda in the exhaust is "Almost" correct (slightly weak at around 1.03, sometimes within MOT limits, sometimes not) and the various gasses, while variable, are what one would expect from a slightly weak mixture with a poor catylist.

Solve the Lambda sensor issue and I suspect that the emissions will either resolve themselves or do so reliably (IE wont have to do it again next year) with a new Cat!

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by Tony Ludford on September 1, 2012, 9:18 am, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
Tony Ludford

I'd also be looking at the HC's and moreso oil consumption. Had a couple of these with cheaper cats fitted by other garages failing MOT the following year due to contamination from worn engines. Pop the oxy sensor out and take a look at it.

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by Kevin Apps on September 1, 2012, 3:29 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
Kevin Apps

Paul
Why not just post the info Aidan has asked for.

Also post the scope capture of the Sensor.

Kev.

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by James Eardley on September 1, 2012, 3:43 pm, in reply to "Toyota Avensis 1.8 1999 poor Lambda behaviour"

Hi Paul

Is this a zirconia sensor or an air/fuel ratio sensor.

If it is a zirconia then with a snap throttle I would expect
To see .8v / fully rich mixture in under 1 second on a scope screen. Use the TPS as something to measure the lambda response against.

Also snap the throttle on a lean lambda switch for best results and to challenge the system.

James

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by Paul Howd on September 2, 2012, 12:16 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
Message modified by board administrator September 4, 2012, 2:19 pm

Thakyou, Though I have had the Pico for some time I keep forgetting that I can record and post waveforms.

I cannot get back to the vehicle before tuesday and will record Lambda/vs tps wave forms (And gas readings) for Cold, Warming and Hot. idle and 2000rpm

Any suggestions for other wave forms?

This is a 12 mile round trip so wish to make as good a use of the fuel/time as possible

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by aidan birley on September 2, 2012, 1:19 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
Aidan Birley

Paul

Are we correct in assuming this does not have a post cat sensor ?

That consistent 0.45 v reading you have seems to me suspiciously to me like a default ecu value (being exactly 1/2 of 0.9v)
As you have no fault codes to explain I asked the questions regarding open /closed loop and measured / live values (sensor connected & disconnected)

As said above you would expect the sensor to rich on acceleration and weak on overrun. the TPS / sensor trace will go some way to proving system.

In my opinion you are flogging a dead horse if you are expecting a cheap cat to give a realistic life expectancy, I always warn the customer (in writing) that it will most often be just a 1 test fix.

cheers Aidan

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by James Eardley on September 2, 2012, 1:39 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"

Hi Paul

How many channels have you got?

Scope TPS-MAF-O2 sensor signal and stick another channel on the lambda heater control wire.

Maybe put 50 seconds on the screen
Turn ignition on and you should see batt volts on the heater control pin from the k46 relay. This will prove the heater element for continuity.

Start the vehicle and look for the ECU controlling the heater. (or check with amp clamp)

Let the car idle and watch for the lambda activity.

Where you go from here depends on the test results.

If you wonder wheter or not to believe the lambda signal challenge it (air leak/propane).

finish off with the WOT tests in my other post.

I am still learning the art of scopes/cars but, coupled with an emissions test I normally get a direction of where to start testing next.

HTH

James

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by Rob Nicholson on September 2, 2012, 8:05 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"

Hi all,

Aren't CAT's now only legally sold if they meet type approval i.e. equivalent in quality to O.E. previously aftermarket CATs were a waste of money and would pass MOT emission levels (providing no other faults existed) but would often flag P0420 cat efficiency fault (if post CAT sensor fitted) after a few miles?

Rob

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by Les Smith on September 2, 2012, 9:12 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
Leslie Smith

Hi Rob. I think you are allowed to fit 'cheap' cats up to 2001. Paul, I take it was a Toyota sensor fitted.
Les

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by aidan birley on September 2, 2012, 9:31 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"

Paul

Les comment re Toyota sensor has reminded me that Toyota used a unusual and unique sensor I think it may be simple wide band sensor,introduced about that time. (Edit I think toyota called this a lean burn sensor.)

google lean burn oxygen sensor and do some research, but looks like that constant 0.45 is good

hopefully some one more knowledgeable will give better information on its working and expected signal output.

It could possibly explain your unusual sensor output

I remember that for a long time these sensors suffered from failed heater circuit and where not available on the after market, but I have more recently success with blue print vehicle specific units

Cheers Aidan

I

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by Tony Sefton on September 3, 2012, 8:43 am, in reply to "Toyota Avensis 1.8 1999 poor Lambda behaviour"
Tony Sefton

If the cars done 200,000 miles and has a non genuine cat and a non genuine 02 sensor and no fault codes logged then I wouldn't waste too much time trying to fix it, I would be pretty sure that if it was a genuine fault then a Toyota would most likely Log a Code. ( And the fuel trims would be out )

If the Guy doesn't want to spend much on it then your on a hiding to nowhere. ??

other than a bottle of fuel treatment and thrash it to within an inch of its life to get the cat hot then the cars a Scrapper. ??

I get fed up listening to customers that tell us how little they want to spend on there cars but expect you to spend hours trying to bodge it and give them a liftime warranty when its done.

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by Paul Howd on September 3, 2012, 3:16 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
Paul Howd

The engine is not an oil burner and the oxy sensor was clean with no evidense of ash deposits. The hc (with a clearly non working cat) was a perfectly reasonable 250 or thereabouts

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by keith brown on September 5, 2012, 4:13 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
Keith Brown

Im with tony on this one,theres only one fault on this job ,the customer has TOLD U he doesn't want to spend any money,hes had a good 200k out of that car & if gen parts were fitted years back you prob wouldn't be posting, i don't fit non gen cats any more
they all ways bite you in the bum!

Re: Toyota Avensis 1.8 1999 poor Lambda behaviour

Posted by John Hancock on September 5, 2012, 6:54 pm, in reply to "Re: Toyota Avensis 1.8 1999 poor Lambda behaviour"
John Hancock

Hi Paul.
we used to mot a lot of these most were taxis and also had to go for council tests. I recollect that the lambda sensors were unique and only genuine sensors should be fitted and they were about £200.
But we found with an oil change and a road test getting the cat really hot then do your cat test, straight away they usually passed.Not worth spending any more of your time on.
hth john.

Re: Toyota Avensis 1.8 1999 - Poor Lambda behavior (Waveforms) #

Posted by Paul Howd on September 10, 2012, 9:57 am, in reply to "Toyota Avensis 1.8 1999 - Poor Lambda behavior # "
Message modified by board administrator September 11, 2012, 2:33 pm

Right, here goes. irrespective of whether the car is eventually repaired, I would like to know what is going on. So here are some traces. I have also attempted to record the emissions at tailpipe but I didnt make such a good job of those (only one pair of hands)

Cold Idle.

corresponding emissions

CO 0.56%
CO2 14.48
HC
o2 0.9
NOX 125
Lambda 1.023

A bit later

Corresponding emissions

HC 148
CO 0.37
co2 14.48
o2 0.8
NOX 79
Lambda 1.02

This is where it starts to get wierd.

Corresponding emissions

HC 308
CO 0.461
co2 14.15
o2 1.08
NOX 73
Lambda 1.024

Later

Emissions

HC 424
co 0.47
co2 14.06
o2 1.20
NOX 76
lambda 1.027

And eventually it does this...

HC 424
o2 1.75
co2 13.82
co 0.363
NOX 80
lambda 1.06

The transition from switching to constant is quite sudden but happened just as the scan went to a new page

These were all at idle.

At speed, once hot, I got this

the red trace corresponds to throttle sensor.

I amm affraid that at this point I wasnt so good at taking emissions readings

when you release the throttle it does this.

Short term fuel trim 3.06%
Long term trim -0.8%

Live data states operation in closed loop!

So what is happening here and why???

Re: Toyota Avensis 1.8 1999 - Poor Lambda behavior (Waveforms) #

Posted by Michael Whitworth on September 18, 2012, 6:33 am, in reply to "Re: Toyota Avensis 1.8 1999 - Poor Lambda behavior (Waveforms) #"
Mike Whitworth - Administrator

Hi Paul,

Judging by your captures and my experience I would suggest (as already stated by Tony and others) that there is nothing wrong with the lambda control system on this car and everything wrong with the cat that has been fitted each year.

I came across these denso Lambda sensors on toyotas years ago and was baffled then but came to realise (as aiden says) they work different to normal zirconia sensors. During warm up and cruise, periods of rapid changing conditions the sensor trace looked very much like a normal sensor, but during idle when warm, periods of slow less active conditions the lambda trace amplitude was much less, to the point where it could flatline. Most scantools will also show current readings in live data for lambda sensors.

So if he doesn't want to spend much let him fit another aftermaket cat and get another 12 months. Otherwise a gen cat will be required.

Mike

M.O.M. Miserable Old Manc

Re: Toyota Avensis 1.8 1999 - Poor Lambda behavior (Waveforms) #

Posted by Paul Howd on September 19, 2012, 8:27 am, in reply to "Re: Toyota Avensis 1.8 1999 - Poor Lambda behavior (Waveforms) #"
Message modified by board administrator September 20, 2012, 12:48 pm

Thanks, I did actually attempt to do a web search as suggested but I am afraid that Google seems to have gone badly downhill over the last 12 months or so. (All I seemed to be able to find was page after page of "Buy Avensis Lambda sensors at shopzilla.com" type nonsense.

We have decided to call it a day on the car on the grounds that I cannot be "Certain" that an expensive toyota cat will fix it. It is a shame though because it is otherwise a sound car!

It would be nice to be able to find out a more detailed explanation as to how this system actually works though if anybody does have some working links.

Paul

Re: Toyota Avensis 1.8 1999 - Poor Lambda behavior (Waveforms) #

Posted by Dave Harney on September 19, 2012, 9:48 am, in reply to "Re: Toyota Avensis 1.8 1999 - Poor Lambda behavior (Waveforms) #"
Dave Harney

Found this on IATN.

A/F Sensor Monitor
The A/F Sensor monitor is similar to the O2 Sensor monitor; however, the A/F Sensor has different characteristics. Therefore, the operating parameters of the monitor also differ.

The A/F Sensor monitor checks for sensor circuit malfunction, slow response rate, and for a malfunction of the sensor’s heater circuit. There is a DTC for each condition for each sensor. A/F Sensors are required to be monitored once per trip; however, the ECM does continuously monitor A/F sensor operation.

When the ECM sees the right conditions, the ECM will test the A/F sensors for performance by measuring the signal response as the fuel injected into the cylinder is varied. The faster the A/F sensor responds, the better the sensor. The results of this monitor test are NOT reported in Mode 5. Mode 6 is used to determine if the A/F sensor passed or failed. The repair confirmation drive pattern in the Repair Manual provides the driving conditions for the ECM to operate the A/F sensor monitor.

Air/Fuel Ratio Sensor
The A/F sensor is similar to the oxygen sensor. It appears similar to the oxygen sensor, but it is constructed differently and has different operating characteristics.

The A/F sensor is also referred to as a wide range or wide ratio sensor because of its ability to detect air/fuel ratios over a wide range. The advantage of using the A/F sensor is that the ECM can more accurately meter the fuel reducing emissions.

To accomplish this, the A/F sensor: operates at approximately 1200°F (650°C), much hotter than the oxygen sensor 750°F (400°C) changes its current (amperage) output in relation to the amount of oxygen in the exhaust stream

Operation A detection circuit in the ECM detects the change and strength of current flow and puts out a voltage signal relatively proportional to exhaust oxygen content.

NOTE This voltage signal can only be measured by using the Diagnostic Tester or OBD II compatible scan tool. The A/F sensor current output cannot be accurately measured directly. If an OBD II scan tool is used refer to the Repair Manual for conversion, for the output signal is different.
The A/F sensor is designed so that at stoichiometry, there is no current flow and the voltage put out by the detection circuit is 3.3 volts. A rich mixture, which leaves very little oxygen in the exhaust stream, produces a negative current flow. The detection circuit will produce a voltage below 3.3 volts. A lean mixture, which has more oxygen in the exhaust stream, produces a positive current flow. The detection circuit will now produce a voltage signal above 3.3 volts.

The A/F sensor voltage signal is proportional to the change in the air/fuel mixture. This allows the ECM to more accurately judge the exact air/fuel ratio under a wide variety of conditions and quickly adjust the amount of fuel to the stoichiometric point. This type of rapid correction is not possible with the narrow range oxygen sensor. With an A/F sensor, the ECM does not follow a rich lean cycle.

You can trim a sheeps wool many times, but you can only fleece it once !

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