Fault codes at start-up (sometimes!)

[garryd]

My '53 plate C5 2.0I petrol auto estate has recently presented a load of error messages on cold start-up. Anti Pollution Alert, Catalytic Converter Fault, plus the Engine Management icon and Service messages remaining lit. The car won't pull away and it runs rough (just like my old MGB used to when it needed a carb set-up). If I switch off and wait 10-20 secs then start it up again it runs OK, pulls away but leaves up the EMU icon and service message. Sometimes the alerts come up the next time I use the car, but not always.

After an episode like this I usually burn the car up the motorway for a few miles keeping it in 3rd gear. This seems to get rid of all messages and the event doesn't happen again for a few weeks.

I have had the plugs changed, and Lexia reports no issues.

The car has only done about 60,000 miles and was previously owned by a disabled person who was a gentle driver.

It's annoying but not seemingly critical. I hope it's not the cat conv. I have had 4 XMs and 2 Xantias, all petrol, with well over 100k miles on each and never experienced this fault - and never replaced a cat either.

Any ideas?


Garry

[Mandrake]

Very strange!

I find it hard to believe that a Lexia reports no problems when it's throwing up all those error messages on the dashboard. Was the Lexia test run while the faults were still present or some time after the faults had cleared themselves ?

Some kinds of temporary faults will be automatically erased after a certain number of engine starts since they last occurred, so its important to get the Lexia on the car ASAP in the case of an intermittent fault.

Unfortunately without getting an actual fault code reading on the Lexia you could just be stumbling about in the dark - if the Lexia is yours I would try to have it ready and plugged into the car BEFORE you start the car in the morning - turn the key on and establish a dialogue with the engine ECU before actually starting the engine then as soon as the errors appear on the dashboard read the fault codes. Also watch the oxygen sensor reading using parameters measurement to see if it is switching high and low correctly. (It will need to warm up for up to three minutes before this happens)

If I had to take a wild guess I would say that you either have a faulty oxygen sensor (sometimes they can be intermittently faulty or just slow to warm up which can trigger intermittent fault codes) or a problem with the cat. As a cat is very expensive you'd need to get cold hard evidence before considering replacing it.

[RichardW]

I'd stick a new battery on it - C5s do all sorts of odd things when the voltage is low - and this is most likely just after you have cranked it....

[garryd]

I'd stick a new battery on it - C5s do all sorts of odd things when the voltage is low - and this is most likely just after you have cranked it....

Hi Richard
This is a nice quick idea (less expensive than a new cat!) I'll give it a try, especially as the car doesn't do many miles (I prefer to use my XM) so it could be getting a bit flat.

Thanks

Garry

[garryd]

Very strange!

I find it hard to believe that a Lexia reports no problems when it's throwing up all those error messages on the dashboard. Was the Lexia test run while the faults were still present or some time after the faults had cleared themselves ?

Some kinds of temporary faults will be automatically erased after a certain number of engine starts since they last occurred, so its important to get the Lexia on the car ASAP in the case of an intermittent fault.

Unfortunately without getting an actual fault code reading on the Lexia you could just be stumbling about in the dark - if the Lexia is yours I would try to have it ready and plugged into the car BEFORE you start the car in the morning - turn the key on and establish a dialogue with the engine ECU before actually starting the engine then as soon as the errors appear on the dashboard read the fault codes. Also watch the oxygen sensor reading using parameters measurement to see if it is switching high and low correctly. (It will need to warm up for up to three minutes before this happens)

If I had to take a wild guess I would say that you either have a faulty oxygen sensor (sometimes they can be intermittently faulty or just slow to warm up which can trigger intermittent fault codes) or a problem with the cat. As a cat is very expensive you'd need to get cold hard evidence before considering replacing it.

Hi Mandrake
No I haven't got a Lexia (not quite true, I have the software and cables, but I haven't got a laptop any more that suits. My XP died and Lexia doesn't work with Windows 8 - and you try buying a computer with anything other than Win 8 nowadays!)
So the fault has gone by the time I get to the garage, and Lexia shows up no faults. I agree about "hard evidence", hence my Q about what to look for so I can put the garage onto it without wasting their time (and my money). I have had suggestions about the oxygen sensor from elsewhere, so I'll look into that before I do anything rash like replacing the cat. Also it was suggested that there is a heater in the air inlet which only comes on in cold conditions. Does this ring a bell?

Thanks for the advice, it's given me something else to look at.
Regards
Garry

[garryd]

I'd stick a new battery on it - C5s do all sorts of odd things when the voltage is low - and this is most likely just after you have cranked it....

Hi Richard
This is a nice quick idea (less expensive than a new cat!) I'll give it a try, especially as the car doesn't do many miles (I prefer to use my XM) so it could be getting a bit flat.

Thanks

Garry

Hi Richard
I've just put in a new battery two days ago and am waiting to see if the fault goes away (I live in hope!) Battery voltage was 12.2 volts even after a good charge (new one is 12.75v) Haynes Manual says anything under 12.4 v indicates a partly discharged battery. As I don't know the history of both the car and the battery and its the beginning of winter, I thought it was worth doing.

Best regards

garry