Intermittent error codes (not) associated with misfire on starting (SOLVED)

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chill
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Posts: 5
Joined: Mon Dec 07, 2020 4:22 pm
Drives: 2000 6N2 1.0 MPI
Location: Nottingham

Intermittent error codes (not) associated with misfire on starting (SOLVED)

Post by chill »

Hi all - first post. I've found this forum useful over the last few weeks while I've been recommissioning a 2000 6N2 1.0 MPI, but now I have a question that might benefit from some specific advice, about some fault codes that reappear intermittently.

The car has stood on my drive for 3 or 4 years, so to get it back on the road I've replaced quite a lot of bits, and I've addressed some known faults that it had before it was parked up. Having stood for so long it needed a new fuel pump, but once that was replaced it started on the first flick of the key - I was impressed! I've now got it to the point where it's running smoothly and sweetly, no warning lights, and it has passed it's MOT.

The problem I'm having is that although it starts first time most mornings, and after a few days of trouble-free running there are no fault codes in memory, just occasionally the first start of the day will lead to a misfire, and the associated fault codes: e.g. 16684, 16685, 16687. This morning was a case in point, and I put it down to the fact that I changed the fuel filter yesterday, and maybe there was still some air in the fuel lines. Is that possible? Previous instances could be put down to dodgy old HT leads, which have now been replaced, so I'm not totally convinced there's a persistent problem, but the fact that it happens at all is annoying.

What bothered me more were some other error codes that seem to pop up whenever there's a starting problem, specifically 17808 (EGR Valve Circuit-Electrical Malfunction), 17833 (Tank Ventilation Valve-Short to Ground) and 18011, which isn't listed in my U281's user guide. So I'm wondering whether those codes are likely to be a side effect of the misfire, or the cause. Since the car runs well most of the time, and these codes don't seem to occur until I have a starting problem, they do seem to be related, but are they the cause or the effect?

I'm still finding my way around this car - how would I go about diagnosing those two error codes?
Last edited by chill on Thu Dec 10, 2020 9:51 am, edited 1 time in total.
chill
New
Posts: 5
Joined: Mon Dec 07, 2020 4:22 pm
Drives: 2000 6N2 1.0 MPI
Location: Nottingham

Re: Intermittent error codes associated with misfire on starting

Post by chill »

To answer my own question, the two codes (17833: evap valve and 17808: EGR) were both present again this morning before I started the car, but it started fine, so it seems they're not related to the occasional starting misfire.

I can clear those codes, but they keep coming back. On further investigation there seems to be a dead short across the evap valve terminals, so I guess that really has failed. I'm going to source a good used replacement.

For the EGR electrical malfunction, am I right that this is purely an emissions feature and will not affect the performance of the engine?
chill
New
Posts: 5
Joined: Mon Dec 07, 2020 4:22 pm
Drives: 2000 6N2 1.0 MPI
Location: Nottingham

Re: Intermittent error codes associated with misfire on starting

Post by chill »

In case anyone else experiences these two faults together, I realised that the charcoal filter evap purge valve and the EGR valve are on the same fuse: #30, 5A. This had blown in my case, presumably due to the dead short across the evap valve terminals. I disconnected the evap valve and replaced the fuse, and the EGR fault now seems to stay cleared. The evap error code (17833) also stays cleared, but is now, not surprisingly, replaced by 17834 (valve open circuit). So hopefully a new evap valve will be all I need, and I won't have to tackle the EGR valve this time.
chill
New
Posts: 5
Joined: Mon Dec 07, 2020 4:22 pm
Drives: 2000 6N2 1.0 MPI
Location: Nottingham

Re: Intermittent error codes (not) associated with misfire on starting (SOLVED)

Post by chill »

Just to (hopefully) round off this thread - I swapped in a good used evap valve and now all the error codes stay cleared. I did get a 16785 (EGR flow insufficient) yesterday, which I'm hoping is just because it was a bit sluggish after not being used for a few years. But I appreciate it could also be clogged up, and will monitor for that fault code. I have a good used EGR valve on the way in case I need to swap it.
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