Front and Rear Pre-Cat fault [Citroen C5 V6 ES9J4S]

[aszaultz]

I'm citroen user in Thailand my car Citroen C5 3000CCV6 24V ES9J4S I have problem in exhaust system. My car shown engine indicator and service light come In lexia have twice faults in injector mode : 1.front pre-cat ageing and 2.rear pre-car ageing. Now I have change front pre-cat, rear pre-cat, and four oxygen sensor up and down stream but problem not solve. I see my catalytic converter in fig 1. number seventeen have cutting I think inner catalytic is empty.
I have change any part below
1. Front pre-cat(11) and oxygen sensor
2. Rear pre-cat(11) and oxygen sensor
3. Iginition coil
4. Spark plug
5. Intake manifold and all seal

I have many question
1. The catalytic converter in number 17 can cause about front-rear pre-cat ageing ?
2. The catalytic converter in number 17, If inner is empty how effect to four oxygen sensor or not effect?
3. Lexia tool in Depollution mode oxygen sensor Front & Rear upsteam value swing around 0.1 - 0.8V (I think is normal operate) but Front & Rear downstream value swing around 0.1 - 0.8V (I think is abnormal because in bosch oxygen manual say "Downstream value hold around 0.4-0.5V)
because The catalytic converter in number 17 inner is empty or not?
4. If I change The catalytic converter in number 17. My problem can solve?

Fig 1

[Ben82]

I am not an expert on this, however I don't believe there are any sensors around #17, and it's all done by the ones around 11 and 13. 17 is really expensive too: £1,711.49 - according to the Citroen Service site (probably more than the total cost you have already paid for 11,13 + the sensors), so you'll want to ensure it is at fault before replacing it.

Maybe quite obvious questions:
1) Have you erased the faults in the Lexia?
2) Are they still showing up as temporary or permanent faults?
3) Did you let the engine warm up before the voltage tests?

[wheeler]

I dont believe there are any sensors in the main cat (17) either so if there were no insides the car wont know.
With the engine warm the upstream sensors should constantly move between 0.1v-0.8v. The downstream sensors should stay at a pretty much constant value but it doesent really matter what that value is. If the up and downstream sensors are both moving up & down between 0.1-0.8v it means the cat on that bank is not working properly.

[Eddie Nuff]

17 is really expensive too: £1,711.49 - according to the Citroen Service site

£708 according to where I got mine from.

[Ben82]

17 is really expensive too: £1,711.49 - according to the Citroen Service site

£708 according to where I got mine from.

Thanks, that's good to know (especially since they deliver to Europe), looks like it's the complete system too (include the pre-cats etc, so a fraction of the cost to buying from citroen)... Sadly for the OP they don't deliver to Thailand.

[aszaultz]

Thank for all advise.
Other Information.
I clear any fault by lexia.... after that two faults 1.Front pre-cat ageing and 2.Rear pre-cat ageing occur again first fault is intermittent fault type after that when used a car again That fault change to permantly fault come with Service and engine light on dashboard.
Oxygen value check. When start in cold engine oxygen sensor Upstream two blank (Front & Rear) is around 0.7-0.8V after that for one or two minutes it swing between 0.1-0.8V in close loop, but Downstream two blank (Front & Rear) is hold for 0.5V four or five minutes after that it swing between 0.1-0.8V In sometime Upstream 0.4V but Downstream 0.7V or other value is Downstream more than Upstream (I think this value is impossible because exhaust gas flow pass Pre-Cat already ??)
I'm measure oxygen downstream value directly due to unplug downstream sensor to ECU and measure directly for ensure ECU no error mesure value is same read from lexia.
I can make circuit for test ECU if I feed 0.5V to downstream signal to ECU then clear fault and observe fault is come again or not??
I have changed pre-cat front and rear for a new part is possible it problem?
Can you advise me If main catalytic converter (17) had broken examples plug or no chemical assembly inside?

Now, my car engine is work fine no missfire or any symptoms exhaust no fume from pipe but smell not good.

Images from lexia; It is fault Front pre-cat ageing and Rear pre-cat ageing below

Thank you for all support.

[Ben82]

This might be an interesting read with a fairly similar issue, he changed a lot of things without much luck, when it turned out to be a fuel supply issue, probably worth looking into, the fuel filter is an inexpensive change, so might be worth starting there.

[aszaultz]

Thank for link I have a plan to change a fuel filter and inspect fuel tank fuel pump any in fuel supply system on saturday. When finish I will tell you for a result.

Thank you.

[aszaultz]

Here my fuel pump. It have fuel around connector plug. Tomorrow I will change new fuel pump.

[Mandrake]

Before you go spending a lot of money on a fuel pump without any real evidence its faulty, you're probably better off testing the fuel rail pressure. If you look carefully you can find a complete fuel pressure testing kit with gauge and adaptors for around the £35 mark.

Not only can you test the fuel pump with this but you can also test the fuel pressure regulator is working correctly, and use it to do injector balance tests to test for faulty injectors.

Regarding your faulty pre-cat codes still being present, when you replaced the pre-cats did you use an after market pattern part ? Do you know for sure that the pre-cats you fitted are good quality ?

If a cat is good you should not see the downstream oxygen sensor swinging high and low like the upstream sensor, it should stay near 0.454 volts. If the downstream cat voltage mirrors the full voltage swing of the upstream sensor this is a sign that the cat is faulty, and this is how the ECU knows it is faulty.

As long as the engine performance is normal and the engine is not misfiring I would be suspicious of the newly fitted pre-cats not doing their job properly.

[Mandrake]

One further suggestion - are you ABSOLUTELY SURE that the cables to the upstream and downstream sensors have not been accidentally swapped over ?

I was just watching the following video and the symptoms are very similar to what you describe:

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You should definitely not be seeing voltage swings on the downstream sensor if the pre-cats are working, however in the above video both upstream and downstream sensors were mirroring each other, suggesting a faulty cat, however the problem was simply that the upstream and downstream cables were transposed. Another clue was that the high low transitions were much slower than they should be.

Double check your connections are not transposed, disconnect them one at a time and make sure the Lexia data shows the correct sensor stops responding...

[aszaultz]

One further suggestion - are you ABSOLUTELY SURE that the cables to the upstream and downstream sensors have not been accidentally swapped over ?

I was just watching the following video and the symptoms are very similar to what you describe:

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You should definitely not be seeing voltage swings on the downstream sensor if the pre-cats are working, however in the above video both upstream and downstream sensors were mirroring each other, suggesting a faulty cat, however the problem was simply that the upstream and downstream cables were transposed. Another clue was that the high low transitions were much slower than they should be.

Double check your connections are not transposed, disconnect them one at a time and make sure the Lexia data shows the correct sensor stops responding...

Thank for your advise.
I have already tested it. I disconnect signal from downstream sensor Lexia 3 fault detect 1. No Signal down stream sensor & Heater for oxygen sensor and value in depollution mode is 0.5V and status not active . Then connect it back lexia3 read value swing between 0.1-0.8 If idle engine it between 0.6-0.8V (Both front and rear pre-cat).
I confuse about sometime downstream value is over upstream (ex. Upstream 0.1V : downstream 0.8V) In actual exhaust had pass pre-catalytic it should be much of oxygen. (change new pre-cat) possible if main catalytic (Number 17. In first post image.) have not a catalyst (ceremic core or chemical part) in cat. It affect to downstream sensor?


Thanks. Today I was changed fuel filter refitting fuel pump and check pressure from regulator to injector rail (3.2-3.3 Bars) it normal operate condition.

[Mandrake]

Fuel rail pressure looks fine so I doubt that's your problem.

If the main cat (number 17) has no oxygen sensor after it the condition of this cat can't be affecting your fault code either.

You need to be careful disconnecting and reconnecting oxygen sensors while testing because you'll temporarily cause a fault code for the sensor which will disable it and put the engine into open loop mode. In open loop mode it will not regulate the mixture based on oxygen sensor reading thus you will not get periodic swings between lean and rich that are a sign of normal functioning. So after you are finished disconnecting and reconnecting the sensors make sure to clear the fault codes and turn off the engine then start it again.

Unfortunately everything that you are describing is indicating that your pre-cats are not working even though you have just replaced them. (You didn't say whether they are OEM or after market types)

When in closed loop mode you should see rapid swings between low voltage and high voltage 2-3 times per second on the UPSTREAM sensors only. The downstream sensors should show a fairly constant reading that may drift over time and should slowly drift until it is near half way - around 0.455 volts.

If you see rapid voltage swings from low to high and back on the downstream sensors that mimics the upstream sensor readings when the pre-cat is HOT then the pre-cat is not working. Remember the cat must be hot to work, so for the first few minutes after cold the downstream sensors will show voltage swings as the cat is not burning any excess fuel in the exhaust, but once they heat up the voltage swings of the downstream sensors should stop and it should settle to a steady mid voltage point.

If you haven't I suggest you watch near the end of that video I linked to see what the 4 oxygen sensor readings should look like - to properly diagnose them you need to be able to graph the data as shown in the Video. Are you able to graph the oxygen sensors in your Lexia software ?

[aszaultz]

Tomorrow I will post four oxygen sensor graph from lexia.

Thank. Mandrake

[Ben82]

Here's what mine looks like for a potential reference:

That has about 60 seconds of driving round the car park, then a few snaps of the throttle, and then a gradual increase of revs to about 3500 and then release. (not sure about it going back into open loop is anything to be concerned about).

(was really only doing it to see if I had fixed my problem with the graphing in Lexia).

Simon: addicted to ScannerDanner too eh?