Technical Lambda sensor connections
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Technical Lambda sensor connections
Hello,
Could anybody direct me to where the plug connector is for the lower lambda sensor on a 1.6 Stilo? I've found the top one fine, but not the bottom!
Thanks,
Del
I think you are talking about the sensor on the cat check that one out as you will see referances to precat and post cat sensors on the parts list for stilo's
I think you are talking about the sensor on the cat check that one out as you will see referances to precat and post cat sensors on the parts list for stilo's
Thanks PNL, I think I mean the post cat sensor! Can it be got at easily or is it an under the car job to get at?
Many thanks,
Del
dropthepuck
New member
Sorry, I can't answer your questions, but my 1.6 is going in to have it's lambdas replaced tomorrow. The garage told me that there were 3 to replace. I may be reading your posts wrong, but it seems like you know about 2. I don't want to think that my garage is going to rip me off on this, even though Mr. Tesco will be paying for it
The garage also told me that only genuine Fiat lambdas will work properly (they are not a Fiat delaership, but Fiat/Alfa "specialists"), since they have tried aftermarket with poor results.
The garage also told me that only genuine Fiat lambdas will work properly (they are not a Fiat delaership, but Fiat/Alfa "specialists"), since they have tried aftermarket with poor results.
I am farely sure that there are two sensors on the cat :chin: as this subject has recently come up for me with regards to a sports cat which I hope to get fitted to the stilo along with a new 4 branch 4-2-1 exhaust manifold and this point came up in the discussion [two sensors on the cat] with regards accessability I think that the cat possibly may need to be removed as its directly bolted to the manifold and not under the car ..if you can remove the metal cat shield you should be able to see the sensors concerned ..good luck
Oh and the comment from dropthepuck is correct dont use any universal lamda [oxygen sensors] use the genuine parts in this case they DO work better 
Only 2 lambdas on the 1.6 as far as I know unless they had a lambda promotion on!
Top one's real easy, connector over by the idle valve
Bottom one's not that difficult either, next to the drive shafts but you will have to get your grubbies on and get underneath
Bottom lambda connector's here
Don't have to remove the cat or anything heavy like that
If doing it yourself then get a special lambda removal socket with the slot down the side for the wires, saves a lot of time
Top one's real easy, connector over by the idle valve
Bottom one's not that difficult either, next to the drive shafts but you will have to get your grubbies on and get underneath
Bottom lambda connector's here
Don't have to remove the cat or anything heavy like that
If doing it yourself then get a special lambda removal socket with the slot down the side for the wires, saves a lot of time
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Many thanks all for your replies.
I'm not too sure if I'll actually change the sensors yet, but its good to know where they connect!
In brief, my Stilo (now 3 1/2 years old) has always ran indifferently; it can be clean and nippy, or noisy and feel like I'm driving through quicksand, or absolutely anywhere in between. I've had it in to garages countless times, and they all report no errors found (I've never had an engine warning light) or that it drove OK for them. Every single trip is a lottery - the car can run badly for 7 trips etc, then fine for 1, then bad for another load, and so on. When I say bad, I mean that the engine/exhaust tone becomes gruff and boomy, and the car feels like it is being held back. At motorway speeds, you cannot hear yourself for the boom! Get back in the car after stopping it, and it might then glide down the motorway, and is a joy to drive.
I've swapped coils out and replaced the map sensor, and the dealerships say there is no updates needed by the ECU. What got me thinking was the other week when NumanR mentioned that the values recorded by the top lambda sensor are stored and used as the base settings for the next trip. I'd often wondered about the lambda sensors but never had the nerve to touch them, but when Deckchair mentioned the fact that if one is unplugged, it will run but on default settings, I thought I'd give it a go. I unplugged the top one and carried on my business. Nothing much happened until the 2nd restart after unplugging it, when I got the expected 'engine fault' spanner (the first time I've ever seen it in all its life is this a Stilo record ?! ) and then I noticed that my car generally ran much more uniformly from trip to trip. I didn't mind if it wasn't great, just as long as in was consistent, hopefully pointing at the lambda sensor as a fault. There were still slight differences in ride quality, so I was wondering next if the bottom post-car sensor may also be having problems. Plugged the top sensor back in after a week, the fault light disappeared on the 3rd restart, and I'm back to pot luck running.
With all this scare that happened over silicone on lambda sensors, I was wondering if something has happened very early in the car's life that has possibly reduced their ability to give out proper readings, without being far enough out to report errors? Could it happen that if a sensor was bad it gave random readings?
Anyway, thanks if anybodys read all this, and thanks Deck for the diagrams. If I can get at the bottom connector, do you think I should unplug it and give it a go?
Thanks all,
Del
I'm not too sure if I'll actually change the sensors yet, but its good to know where they connect!
In brief, my Stilo (now 3 1/2 years old) has always ran indifferently; it can be clean and nippy, or noisy and feel like I'm driving through quicksand, or absolutely anywhere in between. I've had it in to garages countless times, and they all report no errors found (I've never had an engine warning light) or that it drove OK for them. Every single trip is a lottery - the car can run badly for 7 trips etc, then fine for 1, then bad for another load, and so on. When I say bad, I mean that the engine/exhaust tone becomes gruff and boomy, and the car feels like it is being held back. At motorway speeds, you cannot hear yourself for the boom! Get back in the car after stopping it, and it might then glide down the motorway, and is a joy to drive.
I've swapped coils out and replaced the map sensor, and the dealerships say there is no updates needed by the ECU. What got me thinking was the other week when NumanR mentioned that the values recorded by the top lambda sensor are stored and used as the base settings for the next trip. I'd often wondered about the lambda sensors but never had the nerve to touch them, but when Deckchair mentioned the fact that if one is unplugged, it will run but on default settings, I thought I'd give it a go. I unplugged the top one and carried on my business. Nothing much happened until the 2nd restart after unplugging it, when I got the expected 'engine fault' spanner (the first time I've ever seen it in all its life is this a Stilo record ?!
) and then I noticed that my car generally ran much more uniformly from trip to trip. I didn't mind if it wasn't great, just as long as in was consistent, hopefully pointing at the lambda sensor as a fault. There were still slight differences in ride quality, so I was wondering next if the bottom post-car sensor may also be having problems. Plugged the top sensor back in after a week, the fault light disappeared on the 3rd restart, and I'm back to pot luck running.With all this scare that happened over silicone on lambda sensors, I was wondering if something has happened very early in the car's life that has possibly reduced their ability to give out proper readings, without being far enough out to report errors? Could it happen that if a sensor was bad it gave random readings?
Anyway, thanks if anybodys read all this, and thanks Deck for the diagrams. If I can get at the bottom connector, do you think I should unplug it and give it a go?
Thanks all,
Del
Still getting that problem are you Dello? That's been a while
LAMBDA
Did the mechanics check the lambda sensor voltage output signals? If the lambda sensor is slow to respond it will give bad running through wrong fuel/air mixtures being supplied to the engine and sometimes it can have a good day and others not
ENGINE TEMP SENSOR
Engine temperature sensor might be inaccurate, giving out wrong voltage but not wrong enough to cause a fault code. Engine thinks it's warmer/colder than it is.
Does it always start well?
What happens when it's having a bad day? Poor acceleration? Lumpy running?
When it's having a bad day is it worse than when you had the lambda disconnected?
LAMBDA
Did the mechanics check the lambda sensor voltage output signals? If the lambda sensor is slow to respond it will give bad running through wrong fuel/air mixtures being supplied to the engine and sometimes it can have a good day and others not
ENGINE TEMP SENSOR
Engine temperature sensor might be inaccurate, giving out wrong voltage but not wrong enough to cause a fault code. Engine thinks it's warmer/colder than it is.
Does it always start well?
What happens when it's having a bad day? Poor acceleration? Lumpy running?
When it's having a bad day is it worse than when you had the lambda disconnected?
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Still getting that problem are you Dello? That's been a while
LAMBDA
Did the mechanics check the lambda sensor voltage output signals? If the lambda sensor is slow to respond it will give bad running through wrong fuel/air mixtures being supplied to the engine and sometimes it can have a good day and others not
ENGINE TEMP SENSOR
Engine temperature sensor might be inaccurate, giving out wrong voltage but not wrong enough to cause a fault code. Engine thinks it's warmer/colder than it is.
Does it always start well?
What happens when it's having a bad day? Poor acceleration? Lumpy running?
When it's having a bad day is it worse than when you had the lambda disconnected?
Cheers Deck,
As far as I know the garages never checked in as much detail as that, they appeared to declare it fit when it drove Ok into the workshop and brought up no errors. I haven't got the money just now to ask people to do it. The car always starts OK, takes about 2 seconds first thing in the morning, and if the engine is even slightly warm, it starts on the turn of the key. It sounds really weird, but you can sort of predict the journey I'm in for from the noise of the car starting, it just somehow sounds better when it will run well ! On a bad trip, it can still get up to speed and revs, but is really noisy about it, and low speed around town driving is simply uncomfortable; there's less power at move off. Even when its like this, it idles solidly, and if you rev the engine when the clutch is in or its out of gear so the engine is not doing any work, the gruffness is gone, only to return as soon as the engine picks up the strain again.
With the top sensor disconnected, the car never once was as bad as it can be with everything connected. Most of the time it was a pleasure to drive (even though it can on occasions be like this with everything connected!) and it only on a couple of occasions had a 'touch' of gruffness, like a very mild version of what I usually get, leading me to think something else might be slightly amiss. I do feel (even though it may be despearion after all this time) that the car is riding much better generally with the top lambda disconnected.
Thanks Deck, and to all for your time so far.
Del.
If you have a multimeter then I'd check the engine temp sensor and see what voltages it's throwing out for various engine temperatures, cold/medium/hot. If it thinks the engine is cold when it isn't or vice versa you can get poor running as if the engine is out of tune. At the least, spray some contact cleaner down in there
Remember though that the voltage at the sensor may not be the voltage that gets to the ECU, a resistance or two along the way and anything can happen. The connector at the engine temp sensor can cause a resistance too which will throw everything out. When it makes good contact then that could be your "good day"
Remember though that the voltage at the sensor may not be the voltage that gets to the ECU, a resistance or two along the way and anything can happen. The connector at the engine temp sensor can cause a resistance too which will throw everything out. When it makes good contact then that could be your "good day"
Nice to be able to get those pics makes life much easier
I gotta do it the hard way crawl underneath and look :bang: my disk wont load on this PC
Yes pictures speak volumes and getting detailed information on the Stilo is like pulling teeth at times
Why won't your disc run? Are you running Vista?
Dello
Here's a useful chart of resistance v temp for the engine temp sensor
With everything switched off, just measure the resistance across the two pins on the sensor. Should be around 2.5Kohms at 20 degrees down to 230 ohms at 90 degrees
If you have EOBD cables and software you can pick up what engine temp your ECU thinks it is on a laptop
Why won't your disc run? Are you running Vista?
Dello
Here's a useful chart of resistance v temp for the engine temp sensor
With everything switched off, just measure the resistance across the two pins on the sensor. Should be around 2.5Kohms at 20 degrees down to 230 ohms at 90 degrees
If you have EOBD cables and software you can pick up what engine temp your ECU thinks it is on a laptop
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Search me it used to the other PC we had but on this one [ACER]the wife has not long bought it wont run the program starts to load [little pages jumping across from one place to the other making me googly eyed but wont go any further ] Vista upgrade is on the way
more fun 
Well vista is going to be installed onto this PC as it was part of the package with the PC see why I like written Manuals [books] now cant you ..PCs can some times be a pain in the Asp :bang:
see why I like written Manuals [books] now cant you ..PCs can some times be a pain in the Asp :bang:Right, found the engine temp. sensor (well I think so, is it the bright green one?), disconnected the connector, and promptly spent an hour trying to get the conductors of my multimeter to touch the terminals with no joy! The conductors have large plastic bits sticking out of the body that kept hitting a pipe and stopped me getting anywhere near it.
Anyway, have invested in a EOBD II usb job to connect to a laptop and hopefully drive around for a while and note everything. Probably makes more sense than unplugging a sensor and giving it a go. I'll keep you informed!
Thanks,
Del
Anyway, have invested in a EOBD II usb job to connect to a laptop and hopefully drive around for a while and note everything. Probably makes more sense than unplugging a sensor and giving it a go. I'll keep you informed!
Thanks,
Del
I've invested in a EOBD II code reader and the software for a laptop to read and graph sensors and codes in real time. I've only done limited testing (some of the places I drive to I don't fancy being seen with a laptop sitting on the passenger's seat!), but I've looked at a few things.
The coolant and air intake temperatures seem to be doing what I imagine is the right thing. First thing this morning before the car was started, they both read 5 degrees centigrade. After 15 minutes, the coolant temperature was at 80 degrees (started climbing quite rapidly from the moment the engine started) and the air intake rose to 21 degrees, which I imagine is due to the engine bay warming up. (The other night when I first tested it, I'd just got home after a longish drive - the air intake temperature said 47 degrees - would this be OK? I'd imagine it is really hot under the bonnet).
What I can't work out is if I've got a big problem with the lambda sensors, and/or (hopefully not) the converter. I've only had the opportunity to use the program a couple of times, and will need to do a lot more to establish any pattern, but I've copied a couple of captures of the graphs here.
Generally, as can be seen in both pictures, the top pre-cat sensor is doing what, from what I've read, is the right thing. It's voltage is quickly going high to low and back. However, the post-cat sensor is doing whatever it wants! The guide with the software says that the downstream sensor should generally stay level. Another place on the internet says the post cat sensor takes the reading to see how the pre cat sensor is doing, and it looks to me like the top one is working OK. I'm really confused!
One thing that I noticed is visible in this next picture. The area outlined with the black rectangle is when I pulled up outside my house, and the engine was idling, with a steady output from the post sensor of about .25 volts. A quick blip of the gas (Circled 1) and then the output goes back to .25v. Another quick blip (circle 2), and after the revs settled again, the output steadied at 0.8 volts. What's going on here?
I haven't had a good ride yet (which the car is capable of when it wants) to look at the sensor output then, and I'm also yet to do the same with the top cat sensor unplugged, which if anyone reads through the thread will recall me saying helped the car generally run much more consistently.
Could anyone (Decks, NumanR ?) tell me what I'm looking at, if anything. It couldn't be the converter, could it? The car has always done this, but yet whenever it wants it can ride beautifully. If the cat was broken, would that allow this? The car has only had one MOT and the emissions were spot on, but the car was riding spot on that day!
Any help much appreciated.
Thanks,
Del
The coolant and air intake temperatures seem to be doing what I imagine is the right thing. First thing this morning before the car was started, they both read 5 degrees centigrade. After 15 minutes, the coolant temperature was at 80 degrees (started climbing quite rapidly from the moment the engine started) and the air intake rose to 21 degrees, which I imagine is due to the engine bay warming up. (The other night when I first tested it, I'd just got home after a longish drive - the air intake temperature said 47 degrees - would this be OK? I'd imagine it is really hot under the bonnet).
What I can't work out is if I've got a big problem with the lambda sensors, and/or (hopefully not) the converter. I've only had the opportunity to use the program a couple of times, and will need to do a lot more to establish any pattern, but I've copied a couple of captures of the graphs here.
Generally, as can be seen in both pictures, the top pre-cat sensor is doing what, from what I've read, is the right thing. It's voltage is quickly going high to low and back. However, the post-cat sensor is doing whatever it wants! The guide with the software says that the downstream sensor should generally stay level. Another place on the internet says the post cat sensor takes the reading to see how the pre cat sensor is doing, and it looks to me like the top one is working OK. I'm really confused!
One thing that I noticed is visible in this next picture. The area outlined with the black rectangle is when I pulled up outside my house, and the engine was idling, with a steady output from the post sensor of about .25 volts. A quick blip of the gas (Circled 1) and then the output goes back to .25v. Another quick blip (circle 2), and after the revs settled again, the output steadied at 0.8 volts. What's going on here?
I haven't had a good ride yet (which the car is capable of when it wants) to look at the sensor output then, and I'm also yet to do the same with the top cat sensor unplugged, which if anyone reads through the thread will recall me saying helped the car generally run much more consistently.
Could anyone (Decks, NumanR ?) tell me what I'm looking at, if anything. It couldn't be the converter, could it? The car has always done this, but yet whenever it wants it can ride beautifully. If the cat was broken, would that allow this? The car has only had one MOT and the emissions were spot on, but the car was riding spot on that day!
Any help much appreciated.
Thanks,
Del
Crikey. Picasso! Well it's certainly not boring is it!
Sensor 2 looks like it's having a whale of a time
OK sensor 1 should be swinging from 0.8 to 0.2 in about a sec which it's sort of doing, not very consistently though but it depends what you were doing with the gas pedal at the time
Sensor 2 should be keeping fairly steady but it's swinging full rich to beyond full lean and staying there so something's up. May not be the sensor at fault as that may be what's coming past the cat but it's not a normal trace at all
Sensor 2 looks like it's having a whale of a time
OK sensor 1 should be swinging from 0.8 to 0.2 in about a sec which it's sort of doing, not very consistently though but it depends what you were doing with the gas pedal at the time
Sensor 2 should be keeping fairly steady but it's swinging full rich to beyond full lean and staying there so something's up. May not be the sensor at fault as that may be what's coming past the cat but it's not a normal trace at all
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Right! Disconnected the top pre-cat sensor, and the car started generally running better. Took a scan while on the motorway doing a steady 60mph :
As you can see, the post-cat sensor kept slowly going high to low and back, but while doing this (the picture was during the constant 60) there was no percievable difference in the running. Again, the sensor could be putting out a steady voltage until a quick blip on the throttle could send it to a completely different place, where it'd stay again for a while before choosing to pick a different voltage. According to the logs, the sensor was at times putting out just 0.04 volts ! Shouldn't this have logged an error with the ECU? It hasn't - the only one logged is 'P0135 - O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)' - not suprising as its unplugged!
Coming home yesterday with the top sensor still unplugged, and the ride was not too good at all - back to its rough ways, so maybe my unplugging the sensor isn't changing much.
Could I ask what I should be seeing for a graph of the post cat sensor on a healthy car? When its mentioned that not much should be coming from this sensor, does that mean it sits at steadily at 0 volts, or 0.5 volts?
Again, sorry for all the questions!
Thanks,
Del
As you can see, the post-cat sensor kept slowly going high to low and back, but while doing this (the picture was during the constant 60) there was no percievable difference in the running. Again, the sensor could be putting out a steady voltage until a quick blip on the throttle could send it to a completely different place, where it'd stay again for a while before choosing to pick a different voltage. According to the logs, the sensor was at times putting out just 0.04 volts ! Shouldn't this have logged an error with the ECU? It hasn't - the only one logged is 'P0135 - O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)' - not suprising as its unplugged!
Coming home yesterday with the top sensor still unplugged, and the ride was not too good at all - back to its rough ways, so maybe my unplugging the sensor isn't changing much.
Could I ask what I should be seeing for a graph of the post cat sensor on a healthy car? When its mentioned that not much should be coming from this sensor, does that mean it sits at steadily at 0 volts, or 0.5 volts?
Again, sorry for all the questions!
Thanks,
Del
Hi Dello
I was trying to find some decent waveforms for you to look over.
Here's a typical one but note this has 2 pre cat O2 sensors (the top two traces)and one post cat but it shows what we want. Pre cat sensors should swig between full rich/to full lean and back again in just under a second. Its response should be able to get to full lean or full rich in about 0.1sec.
The post cat sensor should also respond every second but should be fairly stable in output voltage
Your 2nd run waveforms with precat sensor disconnected looks normal as the downstream post cat sensor, realising there's no upstream O2 sensor output, tries to wake up the sensor by giving it some rich to think about
So going back to your first waveforms- the pre cat sensor
is it switching from full rich to lean every sec? Not really
Is it reacting quick enough ie 0.1sec? yes
Is the post cat sensor steady? No
But "don't shoot the messenger" and assume bad lambda readings are a bad lambda sensor. The readings just say how much oxygen is present and may be truly what the sensors are experiencing. A bad plug, injector, coil, exhaust leaks can all affect oxygen in the exhaust
Have a look at these links
http://homepage.mac.com/edyjun1/S4/Lambda%20Sensors.htm
http://www.picotech.com/auto/waveforms/lambda_zirconia.html
http://www.fordscorpio.co.uk/easyguide.htm
http://www.lambdapower.co.uk/
Happy reading
I was trying to find some decent waveforms for you to look over.
Here's a typical one but note this has 2 pre cat O2 sensors (the top two traces)and one post cat but it shows what we want. Pre cat sensors should swig between full rich/to full lean and back again in just under a second. Its response should be able to get to full lean or full rich in about 0.1sec.
The post cat sensor should also respond every second but should be fairly stable in output voltage
Your 2nd run waveforms with precat sensor disconnected looks normal as the downstream post cat sensor, realising there's no upstream O2 sensor output, tries to wake up the sensor by giving it some rich to think about
So going back to your first waveforms- the pre cat sensor
is it switching from full rich to lean every sec? Not really
Is it reacting quick enough ie 0.1sec? yes
Is the post cat sensor steady? No
But "don't shoot the messenger" and assume bad lambda readings are a bad lambda sensor. The readings just say how much oxygen is present and may be truly what the sensors are experiencing. A bad plug, injector, coil, exhaust leaks can all affect oxygen in the exhaust
Have a look at these links
http://homepage.mac.com/edyjun1/S4/Lambda%20Sensors.htm
http://www.picotech.com/auto/waveforms/lambda_zirconia.html
http://www.fordscorpio.co.uk/easyguide.htm
http://www.lambdapower.co.uk/
Happy reading
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