My Seicento 900 SX failed big time on emissions, I've got one week to get it sorted for a re-test, I was searching for a solution, but failed so far - need your help, guys. To start, I bought it as faulty, had short circuit to chassis on the left front indicator, that blew two fuses. Battery was completely flat for over a week, car has 41000 miles on the clock and apart from emissions being too high it passed on everything else. I've bought VAG cable and checked for faults, it came up with the following (screenshot):



After resetting the faults it seemed to be better, but went back to as previous. It seems to missfire when revving, has passed all tests on IAW ECU, on gauges shows temperature raising as it warms up, lamba in the lower right corner goes into the red (rich) as soon as I touch the accelerator. Not sure what should happen there, as never used the software before. As said, it seems that it reads the temperature, pressure, lambda readings - but it seems like it doesn't take any action when lambda is showing it's running too rich in fuel. Please advise. Thanks.

the water temp sensor being faulty can cause it to become rich

Changed the temperature sensor and plugs, all plugs got black residue over them due to running rich, cables seem bit dodgy, especially the first from the left, you can tell by the look of the plug connector that it's been loose, tightened them, runs better, but don't think it's right still.

Also, the temp sensor that was on it was made to house the rubber cap on top (to seal the connection), the replacement was longer with protruding neck (old one was flat at the end), but the weirdest thing is that it shows the temperature right (seems lower than the old one, although they should all show it the same way, I think) but the temp warning light on the dash starts to glow dimly when it reaches around 80°C however the fans were kicking in fine on the old sensor without lighting the indicator (I think), and this sensors lits the indicator but fan stays off?

What should be the normal stage, as I never had the chance to see how it seems 'normal' and how it reads on the software? Should it go into 'rich' on lambda gauge on the software part when I accelerate and keep it above 2000 rpm and what does that indicate? Is it showing that the lambda sensor is reading it ok, but the ECU doesn't react upon, or is it ok? Thanks.

Two things.

On the 900 (899) the sensor for the light is not the same as the sensor for the ECU.

You also now have the wrong sender for the light.

The light sender you have is for a gauge, hence why it glows dimly, so that needs changed for the right one.

You need to check the ECU temp sender values as thats the one more likely to be causing your emissions problems.

Cheers

D

Right... I've replaced the sensor (looking from the front of the vehicle) on the left side on top of the engine, where's the sensor sending signals to ECU placed? This would make perfect sense, however I thought as if there's no gauge for temperature, there will be only one temp sensor - it's make sense though to double check and put two in the system...

aquilaalba said:

Right... I've replaced the sensor (looking from the front of the vehicle) on the left side on top of the engine, where's the sensor sending signals to ECU placed? This would make perfect sense, however I thought as if there's no gauge for temperature, there will be only one temp sensor - it's make sense though to double check and put two in the system...

Click to expand...

Sensor for the gauge/light is on the cylinder head.
Sensor for the ECU is on the thermostat.

Swapped the ECU temp sensor (blue top, thanks guys), works better, but still runs rough a bit. Not sure about the effect on emissions, will see tomorrow as going for a retest. I found a small split on the vacuum pipe going from the little filter-like thing (connected to the MAP sensor) into around the injection part. Swapped it round and again, it seems better. I will try to replace it tomorrow, that one should be easy, as it will only need one long pipe. The thing that worries me, that someone was untidy with the other vacuum (?) pipe - the lot of them, different dimensions - and it might have few splits as well.
The other thing is that it came up with the lambda sensor (O2) fault, which I've cleared, but there's no change to the lambda gauge when I rev it up, it used to go into rich, now is just stuck in one position. Is there any way to force lambda to kick in again?

I think you are thinking back to front.

The Lambda 'fault' wasn't a fault with the lambda sensor it was a fault with the induction system causing the lambda to try and resolve the issue.

Now that you have resolved the issue, and the split hose is most likely the problem, the lambda is now happy.

Cheers

D

Thanks for that, will let you know tomorrow if it passed, also will try to get that pipework renewed, if not, sealed temporarily with insulation tape and will look for proper solution. The more I'm under the bonnet of this little thing the more I learn it - mainly with your help and the old rusted thinkbox upstairs...
One day I will have it all running perfectly... I hope so, anyway...

Just came back from the MOT re-test - passed, although it had some problems to start with, it was going way over again, but after it warmed up and got revved up, it seems that it managed to clean/sort itself out, as dropped to manageable standards. Will still need to look at it, check the pressure pipes, replace the coolant and change the HT leads, but at least I can use it now. Thanks guys, all help was much appreciated. Will probably need more of that the further I go into my Seicento, but once again, big thank you. :worship: