Help - VW Polo 9N AWY 'check engine' light on

Help - VW Polo 9N AWY 'check engine' light on

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acme15

Original Poster:

20 posts

130 months

Sunday 26th October 2014
quotequote all
Hi all,

My car is a 2002 VW Polo 9N 1.2 6V AWY with 138K on the clock. All service parts/common wear & tear parts etc have been refreshed during my 2 years of ownership, and it has been regularly serviced and looked after.

I was driving home earlier today and the 'check engine' light (orange engine shaped light on the left side of the speedometer) came on out of the blue.

There are no strange sounds coming from the engine, the engine idles smoothly, the engine pulls fine through all gears, there is no "lumpiness" and no misfires throughout the entire rev range.

I have checked all fluids and all seem fine, I have checked all hoses and plugs as much as I could at the side of the road (just visual checks for obvious splits or loose hoses/disconnected plugs etc) and there don't appear to be any obvious issues.

I have tried various methods which are supposed to clear lights/errors (I don't know how many [if any] of these are genuine methods but I tried these regardless):

- Pressing in trip button for 2 seconds and turning to the right
- Pressing in trip button for 2 seconds with key turned to lights position, and turning to the right
- Pressing in trip button, holding, turning ignition to lights position, holding, turning ignition off, removing keys, and releasing button

I have also tried to reset the ECU using these two methods (Again, unsure if either of these are genuine methods, but I tried them regardless):

- Disconnecting negative terminal for 15 minutes and re-connecting, then starting engine
- Disconnecting negative terminal for 3 minutes, then re-connecting, then turning ignition to lights position, waiting 3 minutes, turning ignition off, removing key, putting key back in, then starting engine

Points to note:

- Engine had a full tank of petrol when this happened, it was cheap supermarket petrol though (Tesco 95) and I usually use Momentum/Ultimate/Super or sometimes Esso 95
- Radiator fan is faulty and non-working (blows fuses) but it has been like this for 2 weeks/500 miles, I have been careful with the engine, and never seen it go above 90 degrees. (replacement fan is in the post)
- The car was involved in an accident a few weeks ago, but it has been fine from after the repairs up until now (again, 2 weeks/500 miles) and it was fine before (never had the light come on)

The following parts were replaced:

- Front bumper
- Front offside wing & arch liner
- Lower front offside wishbone
- Front exhaust
- Radiator
- Front offside headlight cluster

The sump pan is dented, but not ruptured at all, and the inner wing was welded.

If anyone could shed any light on the subject or give me things to try, it would be much appreciated!

I do not have access to any diagnostic equipment, but I will be phoning my mechanic ASAP to get him to have a look at the fault codes and give the car a general once over to see what is wrong.

Finally, would you advise against driving the car while the check engine light is on persistently, even if there are no obvious issues?

Kind regards!

VWDaz86

387 posts

185 months

Sunday 26th October 2014
quotequote all
I think you're overthinking the situation. You need to get the codes read first and go from there. There is no way to clear the light other than via a reader or the ecu believes the fault is no longer present and self extinguishes.

It could be anything from a sensor to software issue. But as you say no obvious running issues I'd probably say a sensor issue is most likely.

Don't worry to much and panic(that's how I read your post). Get it read and let us know what code.

miniman

24,826 posts

261 months

Sunday 26th October 2014
quotequote all
Yep, don't panic, get the codes read and go from there. Probably a Lambda sensor.

acme15

Original Poster:

20 posts

130 months

Sunday 26th October 2014
quotequote all
I haven't got the codes yet, but I took a closer look in the engine bay and traced the wires for the lambda sensors, and one of them looks like it has been chopped, re-soldered and taped up in the past, and further down the same wire, it looks like the wire got pinched in the accident and the insulation is ripped and there is bare wire showing.

SteBrown91

2,360 posts

128 months

Sunday 26th October 2014
quotequote all
acme15 said:
I haven't got the codes yet, but I took a closer look in the engine bay and traced the wires for the lambda sensors, and one of them looks like it has been chopped, re-soldered and taped up in the past, and further down the same wire, it looks like the wire got pinched in the accident and the insulation is ripped and there is bare wire showing.
Theres what likely lies your fault. Most of the time an engine check light with no other symptons is as simple as a MAF or lambda sensor.

Deerfoot

4,897 posts

183 months

Sunday 26th October 2014
quotequote all
Do your brake lights work?

acme15

Original Poster:

20 posts

130 months

Sunday 26th October 2014
quotequote all
SteBrown91 said:
Theres what likely lies your fault. Most of the time an engine check light with no other symptons is as simple as a MAF or lambda sensor.
Is the car okay to drive in the mean time? Alternate transport is a little inconvenient, what with the train station being a 30 minute walk, and then another 30 minute walk from the station to work.

Deerfoot said:
Do your brake lights work?
Yes they do. The brake light switch failed last year and was replaced, it brought up the EPC light rather than the engine light. If that is what you were thinking it could be. smile

Deerfoot

4,897 posts

183 months

Sunday 26th October 2014
quotequote all
acme15 said:
Yes they do. The brake light switch failed last year and was replaced, it brought up the EPC light rather than the engine light. If that is what you were thinking it could be. smile
Yes, I had that on my old Polo but I couldn`t remember exactly which light came on. I do remember it was strange that a broken brake pedal switch turned on a dash light that was seemingly unconnected to the actual fault.

Good luck with your fault finding.

bigjobbo

151 posts

209 months

Sunday 26th October 2014
quotequote all
I'm guessing at camshaft position sensor if it's not already been done, but there are a couple of fault codes that require a software adjustment so a scan is a definate requirement.

acme15

Original Poster:

20 posts

130 months

Monday 27th October 2014
quotequote all
Have driven it another 20 miles or so since this thread as I don't really have much other option, still can't detect any difference at all, of any kind. So I am pretty much certain that it is just one of the aforementioned sensors.

What would be a good bet if I were to buy a cheap(ish) diagnostic reader from eBay?

acme15

Original Poster:

20 posts

130 months

Tuesday 28th October 2014
quotequote all
Just bought one at the recomendation of an ex VAG techie over on the ClubPolo forums. It should be with me tomorrow with any luck.

acme15

Original Poster:

20 posts

130 months

Wednesday 29th October 2014
quotequote all
Right so, the OBD reader returned three fault codes:

16804
17978
16556

The first one, 16804 isn't in the accompanying booklet, but Google suggests that it is "Catalyst System; Bank 1: Efficiency Below Threshold"
The second one, 17978 isn't in the accompanying booklet, but Google suggests that it is "Engine Start Blocked By Immobiliser"
The third one, 16556 is in the accompanying booklet, and it is "Fuel Trim: System Too Rich: Bank 1"

I am not concerned about the second one regarding the immobiliser, as the engine starts and runs fine, there have been no issues with the immobiliser, and I think it may have happened when I had a third party key programmed for the car.

So looking at the first and third ones then:

16804 - Catalyst System; Bank 1: Efficiency Below Threshold
16556 - Fuel Trim: System Too Rich: Bank 1

Any ideas? I'm guessing that 16804 is that lambda sensor, or could it be the cat? Is 16556 likely to be related and/or possibly the cause of 16804?

Should I clear them and see if they come back, first off?

miniman

24,826 posts

261 months

Wednesday 29th October 2014
quotequote all
1. Italian tune-up
2. Clear fault codea
3. See what happens

acme15

Original Poster:

20 posts

130 months

Wednesday 29th October 2014
quotequote all
1. Done
2. Done
3. Drove 25 miles after resetting, cycled the ignition a few times as well, no lights or codes yet.

acme15

Original Poster:

20 posts

130 months

Friday 31st October 2014
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200 miles in, no issues yet.

SMB

1,513 posts

265 months

Friday 31st October 2014
quotequote all
acme15 said:
200 miles in, no issues yet.
16804 can be caused by a small hole in the exhaust around the sensor/cat area. If so it could return after anywhere between 25 and 300 miles. Might just be a small hole, listen for any raspiness when gently revved.

acme15

Original Poster:

20 posts

130 months

Friday 31st October 2014
quotequote all
The front exhaust section is brand new, and the mid and rear sections are less than a year old. There is also no raspiness, so I don't think it is that. smile

acme15

Original Poster:

20 posts

130 months

Tuesday 11th November 2014
quotequote all
Both the codes are back after around 600 - 800 miles.