Technical Need help please with emissions failure and various fault codes

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Technical Need help please with emissions failure and various fault codes

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Hi again all

So, the 07 1.2 8v Grande Punto my daughter bought earlier this year, has failed the MOT (NCT here in Ireland) twice in the last month on emissions

After the first failure, I advised her to put in some petrol additive and drive the car hard for a few days, as it never gets a decent drive during the week. She travels maybe 1-2 miles to work and the same home, and some short drives on the weekend, but rarely more than 5 or 10 miles

Initially when we bought the car, the engine light was on, but the guy I bought it from, told me it passed the test every year, despite the light staying on. I read the code at that time, and it gave a P0135 code relating to the heater circuit for the pre cat oxygen sensor. We put it through the test in February, and sure enough, it passed with no problems with emissions.

This time, the HC and CO figures are way off and the lambda reading is very low, so after 2 fails, I got the car back from her, read the codes, and now there are 3 codes showing

P0135 Heater circuit Bank 1 Sensor 1
P0141 Heater circuit Bank 1 Sensor 2
P0443 Evaporative Emission Control System Purge Control Valve

As my son previously had 3 Mk2 Puntos, I took off both oxygen sensors, and then what I understand to be the Purge Control Valve, from one of his old cars which is no longer running.

I changed the purge valve, and then tried to educate myself on how to read oxygen sensors with a mulitmeter

From my tests, both of the oxygen sensors in her car, seem to read approx 10 ohms on the heater circuit, so it would appear that they are actually ok, so I haven't changed them yet, but despite using Torque to clear the engine codes, and running the car etc, all 3 codes re-appear instantly once I read again

I am now wondering if all 3 of these errors share a common fuse or wiring, or just in plain English....where to go from here??

Some guys I know were telling me to change the precat sensor, others saying both, others saying change the catalytic converter, but as it's a 12 year old car, there is no point in stupidly throwing lots of parts at it and hoping that one off them might fix it!


I'd really appreciate any help I can get on this.

Btw, I don't own a copy of Multiecuscan, or have the correct cables for it, and as the re-test is due again in a few days, I would never get it in time from the UK to Ireland, so for the time being, I'm going to see if anybody can help before the last date she can bring it for re-test without having to pay full price for a new test again
 

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The oxy sensor heater is to help the sensor get hot quicker after a cold start, but once running the exhaust keeps it hot. When it passed the test, the engine was probably nicely hot, so the duff heater circuit had no effect.

It would appear that the primary oxy sensor is dead. If either of the used ones you have are known to be good, fit that. If the readings from this sensor are poor, the ECU will fuel the engine with a known setting that will allow it to run, but will generally be rich, which is what the figures are saying.

The secondary sensor is less important, only acting as a check that the catalyst is working, but this will nto be relevant if the first sensor is giving poor readings.

Replace the primary sensor, getit up to temp, clear the codes and give it a run to see what happens.
 
Thanks very much for the reply

This is where I'm a bit lost though
I assumed the sensors were gone and needed replacing, so I removed both from the MK2 Punto, but it seems that using a multimeter and getting an ohm reading across 2 of the 4 wires determines if the sensor is good or bad

So, I checked the 2 from the MK2 Punto and the secondary one is not giving any reading, but the primary one reads 10 ohms.

Then I decided I would use the good one on her car, but when I disconnected both sensors on her car, they also both read around 10 ohms, so does this mean that the 2 on her car and the primary sensor from the old MK2 ones are all working?

If so, I can't see how it will make any difference swapping them over, or is there something else I am missing?
 
There are four wires top each sensor, and effectively two parts.

Two wires are used by the sensor, to show a changing voltage to the ECU. I've no idea what resistance this circuit should show, but even if reading correctly may not indicate whether the sensor is working. More important is whether this reading is changing correctly due to changing oxygen levels - difficult to test.
Another wire is the heater element feed, and the last one is earth. (Early sensors had three wires, until failing earth paths via the exhaust prompted the additional wire.) Again, the heater element may well show a good resistance reading, but not perform properly.

If either of the Mk2 sensors were known to be good, working correctly, and the wiring and connectors look compatible, fit it and give it a try.
 
Ah ok. That makes more sense.

This is why I posted here, as from my limited reading up on O2 sensors, I assumed if the resistance reading on the heater circuit was ok, it meant the sensor was ok.

I'll try swap them tomorrow and post back with results. I'm not 100% certain that they are the same, but I have seen the same sensor listed online for the MK2 and also the Grande Punto 1.2 8v, so I'm fairly confident they are interchangeable.

By the way, I also checked the air filter, as its running so rich, I was afraid it might be starved of air, but the one that is in it looks almost brand new.

On another note, the purge valve error which wasn't there at the beginning of the year when she bought it... Would it be possible that its actually ok and just 1 error throws other related error codes on the engine management?


I changed it anyway, and I assume I changed the correct part. It's on the passenger side of the intake manifold just back at the firewall.
 

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But lambdas itself are OK and (as per error codes) is faulty only their heating part. After cold start I believe you should be able to measure 12V on cables responsible for heating of labdas. If you measure 12V, then lambdas are dead (but I don't believe that both lambdas are failing at the same time...that's almost impossible). So I think that problem is somewhere in electric part of vehicle (some fuse for lambda pre-heating, some relay for it...). I'm not electrician, but I think that there must be some relay and once engine temp reach XY, then ECU will stop pre-heat lambdas so it trigger that relay to stop adding 12V to heating part

Regarding PCV error - I thing that ECU is opening this valve mainly at hot idle, or during braking with engine (deceleration). I also believe that valve is wotking on 12V and it simply open/closes, so when you remove it and connect directly to battery, you can check if it's opening/closing. If yes, then problem can be in connector to PCV valve (just clean it). If this error code is related to lambda heating circuit problem I don't know...maybe yes. But as 1st definately lambda codes are more important to solve
 
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Just to add,the pcv caused an eratic idle on a fiat I take care of . After a year of faff a second hand replacement cured it.
 
So, I didn't get near the car today to change anything as I got home late

Was outside briefly now, where it's bloody icy and spitting rain!

Quick observation-

Disconnected the primary O2 sensor, started the car and brought it to operating temp more or less (about 80-85 degrees coolant temp)
Used my multimeter to read the 2 wires from the sensor that are NOT the heater circuit. Got a reading of around 0.8 to 0.9 volts, so it appears to be working fine.

Then I let the car cool down a bit and plugged the sensor back in and started the car again and used my OBD adapter with the Torque app and monitored the O2 sensor voltages while the car was ticking over. The voltage on sensor 1 seems to sit at a constant voltage of maybe .6 volts, and sensor 2 appears to be more or less sitting at a constant zero, with the odd spike. (see the attached pic)

My understanding is that sensor 1 should almost cycle constantly from 0.1 volt to 1 volt and create a wave pattern, and that sensor 2 should always sit around 0.3 - 0.5 volts and remain fairly steady.

So finally, I unplugged the sensor again and probed the connector for the primary sensor when the car was running, and the only wire I could pick up voltage on, was giving 1.88 volts. Surely this should be reading 12 volts?
 

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Hi Mike,

O2 (Lambda) sensors need to reach 600°C to start working, even with coolant at 80-90° the exhaust gases are not that hot, so the ECU doesn't check the A/F ratio at idling, nor does it during acceleration/deceleration. Actually it does adjust A/F only when cruising ...
The method of using a multimeter is a bit short, you'd better use an 'o'scope where you'd see the real wave produced by the sensor. However, multimeter troubleshooting can give you a rough idea of the sensor. The 0,6ish volts you read in your graph is the reference voltage only, this will start fluctuate between 0,1 and 0,9 volts once the sensor will be warm enough. To do so you need to bring the engine around 2500 RPM. The multimeter has to be connected in // with the existing connection ...

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)
 
So, with the dark evenings etc, I just never got this sorted
Changed the primary O2 sensor for the "good" used one I took from the other car

Used Torque app with OBD reader and got the car up to temp, and then used the O2 sensor monitor feature, and yet again, the O2 sensor has absolutely no fluctuation in voltage output when held at a constant 2,000 or 2,500 rpm.

As I don't have an opportunity to get to the car until late each day, I'm going to have to bring it to somewhere and let them diagnose the issue, but to me, the fact that my 3 errors are all for items on the same circuit, I am sure the issue must be down to that circuit, whether it be fuse/relay etc. It just seems too much like conicidence that both O2 sensors and the purge valve, and ANOTHER O2 sensor off a different car are all reading with errors.

I'll update once I get it sorted, and hopefully it will help somebody else in the future
 
OK. It got the better of me

I just couldn't let it go to somebody else

Went over it all with a fine tooth comb again, and lo and behold, what I suspected from the start!!

It turns out there was a fuse missing from the fusebox under the bonnet.

I went back over the wiring diagram and it referred to F27 fuse, and that holder was empty. Popped in a 15 Amp fuse, and started the car and within minutes, the O2 sensor graph is fluctuating up and down as it's supposed to.

Now to drive the car a bit and clear the errors and put it back through the test again.

Hopefully this might help somebody in the future
 

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According to the provided drawings F27 feeds the 02 sensors' heaters, so I guessed it had been cheched...
 
Hi again all



P0135 Heater circuit Bank 1 Sensor 1
P0141 Heater circuit Bank 1 Sensor 2
P0443 Evaporative Emission Control System Purge Control Valve

Those three were related to the same (missing !?) F27 fuse as per drawing provided ...

BRs, Bernie
 

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Recent purchase.. never subjected to a test in their ownership ;)

Well KINDA!!!


Car was bought in Feb this year with Engine light on
Test had expired, so put it through a couple of days after buying, and it went through no problem

She moved away from home, has been driving it for last 6 or 7 months, and the test was due again in October. Put it through and it failed on emissions, so I told her to add cleaner to fuel tank, drive the hell out of it and try again. Massive fail again, so I brought it back here and spent the last couple of weeks grabbing a few mins anywhere I could, but was about to give up until despite not being able to read electrical drawings, I used logic and saw that all 3 items throwing up an error, were all fed by the same fuse, and turns out it wasn't even in the fusebox!

Now the real baffling thing for me, is my daughter didn't even know there was a fusebox in the engine, and the only person to ever do any bits on the car was myself, so it LOOKS like the fuse was never there since it was bought, but I don't get how it passed the first test!

Anyway, if you pull that fuse on your own car, you will see that the car will actually run without it, but now we all see that it effectively disables the O2 sensors AND purge valve!

I'm as baffled as everyone else, but also delighted I finally got to the bottom of it
 
Those three were related to the same (missing !?) F27 fuse as per drawing provided ...

BRs, Bernie

What really made all of this so confusing is, it is referred to as F27, but you can see in my photo of the fusebox that it's actually numbered as 34, so I thought I read the wiring drawing wrong and read F28 instead, which is the lone fuse under the black relay above this empty slot
 

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My guess here is that something happened in the past and the owner took off the fuse as a spare for another that blew, and never replaced it since the car was running without it ??

BTW, the engine runs on fixed A/F value (internal maps) when it misses O2 signals, also when engine's cold, idling or in acceleration/deceleration phase. You'll probably notice a better mpg ...

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)
 
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