Fabia 1.2HTP - Misfire - P0303 - 006 - Short to Plus

[arobertson]

Been loving my 57 plate Fabia for the last couple of months, fitted remotes to the central locking, got some winter typres on steel rims, but today it limped home with a blinking check engine light and running rough.

 

The error code that comes out is:

 

16687 - Cylinder 3: Misfire Detected

        P0303 - 006 - Short to Plus

 

I tried swapping the coil pack but the problem still came up on cylinder 3.  I read lots about cylinder 3 and valve problems with the 1.2HTP but the 'short to plus' gives me hope that this is a wiring or spark plug problem (although I don't know if plugs can cause this error).   I couldn't find much about this particular error, mentioning the short to plus on line.

 

Does anyone have tips for diagnosing this?  I've just come from a Smart car (10 years and over 100,000 miles) which i got to know very intimately (it was on it's 4th turbo).  Wasn't really planning to get to know the Skoda so soon but it looks a hell of a lot easier to work on!

 

[Toxicvrs]

Check for any rubbing through in the cable channeling

[xman]

If the plugs are more than 30,000 miles old, change them (they're about £3 - £4 each at gsf or ecp).

Usually the fault is due to faulty coil, resulting in running on 2 cylinders (really rough, little power). If disconnecting suspected coil makes no difference, then that's the culprit.

Changing faulty plugs or coil will not automatically clear the fault code until the engine has run a fair bit and been started a number of times unless you clear the code with Vcds.

Edited 28 February, 2015 by xman

[arobertson]

Been poking around the engine today.  Basic question; what cylinder is number 3?  I've stripped the wiring loom covering off back to the ECU but there's no damage on any wiring to coils (there was some damage to other wires but nothing that could cause shorts)

 

I'm using VCDS-lite to check and reset codes that come up BTW.

[xman]

No 3 is the one closest to the gearbox. No.1 closest the pulley end.

Check the wires for continuity from the pk connector to the ecu if you can.

Otherwise likely to be a faulty coil, they cost under £20 from gsfcarparts using discount codes, most weekends they have 33% or more discount code available. This weekends code is GSFCP35 i.e. 35% off -> £14.70

From experience, I've found that worn/faulty plugs can kill a coilpak as the spark voltage is elevated and the marginal insulation breaks down and zaps the electronics in the pak. So don't leave old plugs in....

Edited 28 February, 2015 by xman

[arobertson]

OK, three is at the gearbox end.  Took the connector off the coil at the gearbox end - fault on cylinder 3 appeared.

 

I've tried swapping coils from 1 - 3 but the fault doesn't track the coil.

 

I've swapped plugs from 2 to 3 (plugs weren't tight), no change in the fault, still appears on 3.  Had high hopes of a grounding issue due to loose plugs and junk under seal.

 

The engine starts fine and idles fine.  Drives for a bit and then I think it's the ECU detecting the fault and shutting down the coil that makes it feel horrendous.  I think if this was an old carb. fueled car it would carry on undetectable until it got a lot worse.

 

Reading other posts about the HTP engine, it seems that valves are a common culprit :-(  I'm borrowing a leakdown tester on Monday from a friend.

 

It's just the short to plus that makes me think it's an electrical gremlin.  Could be in the ECU I guess, not sure how to check that.

[xman]

Ok so idling fine eliminates the coils, Short to plus fault can be given by an open circuit on the ground (non supply) side. So a dodgy connector, or a wire with a broken core can cause it. Meticulous continuity testing the wires from the pak connector back through the loom to the ecu connector while pulling/bending the loom (in moderation) would find it.

Edited 28 February, 2015 by xman

[arobertson]

Sorry, I should probably be clearer. Everything feels fine until the ecu starts shutting things down. I think the idle is fine until I rev up and down a few times to put the engine under a bit of load. I can then feel a slight shudder at idle but there are no warning lights and no error codes at that point. The idle doesn't feel that bad at any time really. It's under load that the problem appears. I think the ecu waits for quite a while before deciding it's a problem.

I will check out the loom tomorrow in detail, it's raining now. I don't understand why the coil works at all if it's a wiring issue. You'd think that it would be a problem that would have gone away with me unwrapping the loom or would cause the coil to completely malfunction due to the continuing short. It never seems to detect the short during prolonged idling.

I haven't tried swapping the injectors yet either but I believe the fault codes usually indicate an injector if it's an injector issue. Will depressurise the fuel line and shall swap them tomorrow to rule them out.

Looking forward to the leak down test...

[arobertson]

Just reading your post again; is there any mileage in trying to bypass one of the wires completely? If it was a resistance issue it might show up under high coil electrical load which is why idle seems fine. I could add a bypass from near the coil all the way to the ecu.

Is the wire you're referring to the main black wire in the connector to the coil? Is this just a local ground for the coil?

[bluecar1]

careful now, proper fault finding and investigation

 

you would never get a job in a skoda dealer as you would show up the master tech :P

[arobertson]

Watched a few interesting videos on diagnosing rough running Skodas and VWs.

 

I like this one:

which ends up pointing the finger at an injector after changing the usual stuff including valves and ECU.  Must've been costly for someone.  Nice workshop with diagnostic tools galore.

 

I still live in fear of the leakdown test but I wonder if 'short to plus' could also refer to part of the injector circuit although I assume that would throw an injection related fault in VCDS?  I haven't fully checked the wiring to the injectors but I'll do it tomorrow and then see if the fault follows the injector when I swap them around.
 

 

Thanks for the help so far.  I'm not clear what could be shorted to what as there's so much plastic and not alot of +ve to short to but at least everything on the Fabia is easier to get to than on the Smart.  You have to mine for the engine on the Smart...

 

It's howling a gale now.  Not a fun time to be out with the bonnet up

[xman]

Reading the original post, the error message does not specify coil or injector.

The "short to positive" message merely indicates that a wire at the ecu connector is not at the expected low voltage condition. It may be a short, or an open circuit/high resistance on another wire to or internal to the pak/injector, such that its not possible to pull down the voltage. I hope you understand what I mean.

You need to check the electrical schematic and be very careful! An incorrect wiring error could blow the ecu. IIRC in vag cars the ground wires are usually brown. And sometimes brown is also used for other non ground connections. The connections to the coilpaks are complex as they are also signal wires that command and receive feedback to/from the ecu.

Its possible for a wire, particularly if flexed a lot, to break its inner copper cores, the outer sheath remaining intact. The cores can still touch but separate under tension/vibration. Another failure mode is insulation breach that allows air/water to enter the wire which corrodes internally and again the cores break.

Vcds is also known to mislead on many occasions, so it might be injectors rather than coil. I would be tempted to swap injectors next.

Edited 28 February, 2015 by xman

[arobertson]

The fun continues; Swapped injector 2 for injector 3.  Still same fault on 3.  Injector three very stiff to get in and out but looks OK.

 

Further wiring loom dissassembly to the injectors but nothing to see so far.  I've been trying to get the connector off the ECU; what am I doing wrong?  It looks like you have to remove some security screws holding the metal cage on.  Am I missing something simple?  I can't extract the usual locking pull mechanism without moving the metal cage but the cage, I would say, is tamperproof.  I tried puting a slot in one of the screws but it still won't turn.  I'd like to get to the ends of the wires at the ECU to check all the cylinder three wires.

 

Any advice on the ECU?

[xman]

Can't advise on the security screws, Google it? Maybe this is similar http://www.goapr.co.uk/support/ecu_removal/cc_3c8.html (shear bolts hold the locking cover)

The following thread is similar fault to yours, thought it may be of interest, also a 1.2 engine

http://www.seatcupra.net/forums/showthread.php?t=311466

Edited 1 March, 2015 by xman

[bluecar1]

be careful removing the connector from the ECU, I seem to remember something in the back of my mind about having to re-enter basic settings if the plug is removed

 

may be totally wrong

 

no doubt someone on here can confirm or deny my dodgy memory

[arobertson]

Xman; thanks for the links, the cage is getting the chop. What a PITA, I can't see it serves any useful propose other than to hinder DIY fiddling.

I saw the other post you linked to a couple of days ago. Checked that out on the battery but nothing amiss. Still to try bypassing the wires but it was sleeting and the hens needed refencing!

Bluecar1; I'm intending to only disconnect the loom to the injectors and coils etc which seems to be downstream of the ecu, i.e., ecu shouldn't know it's been powered down. Would think a connector disconnect was the same as a battery disconnect from the ECUs point of view? On the Smart, disconnecting the battery for a few minutes resets the ECU and it has to relearn the clutch and gearshifts.

Going to work in the Smart tomorrow. It only has a minor misfire at 2800-3200rpm, but its had that for almost 2 years and only at heavy throttle.

[arobertson]

The Smart is dead... alternator seized from standing for two weeks and threw the belt which also drives the cooling pump of course....  nice warm engine and but no heat to the cabin, brings back memories of 1275cc Mini Mayfairs...

 

Back to Patient #1; Discovered a leak in the exhaust (junk clamps rusted through) and a split in the vacuum line to the servo.  Replaced the vacuum line with temporary garden hose and tried jubilee clips around the exhaust clamp which didn't really work.

 

It has improved slightly, I drove it 6 miles and only got rough running due to cylinder shut down once.  It still judders between 1800 - 3000 rpm but above or below that it seems fine.  It could be that at high speed the rotating inertia is enough to mask any juddering however, riving at above 3000rpm wide open throttle seems fine.  It's just getting there where I have to be careful.  Did this through warmup and to working temperature as well.

 

In 1998 I had a Vauxhall Nova 1.2 which would barely rev due to an exhaust leak.  Some kind of back pressure resonance effect in the exhaust system.  Wondering if there's something similar going on in the Fabia.

 

Now taking my Wifes car to work while she gets her Dads car...

 

[arobertson]

Compression test; no compression on 3. Did it twice as I was surprised there was literally no reading. Surprised it idles so well at all. Damn.

[fordfan]

Did you try a wet and dry compression test?  My thoughts are that a misfire on one of these engines that doesn't move with relocating the coil pack on the offending cylinder is usually down to something mechanically wrong with that cylinder.

 

If a wet compression test made no difference, I would suspect a valve problem. An incorrectly seated exhaust valve doesn't usually make a big difference on the compression test, it sounds as though the valve is cracked.  If you can, a leak down test would help more to ascertain the problem before you remove the head.

[arobertson]

Leak down kit is here but I need to borrow a compressor. Will have to wait until the weekend as I am away for the rest of the week.

Is there a Haynes that covers the 6v engine? I couldn't find an online how-to and the Haynes I found was for the Fabia I. Is the engine the same as the Fabia I?

[arobertson]

Just to finalise this thread after over 6 weeks of messing around and spending some money on parts swaps.

 

The local garage identified an injector problem (on for 15ms too long) and replaced the injector.  This changed the miss-fire slightly but the car was still miss-firing and going into limp mode.  They were the most honest garage I've ever been to and didn't charge a penny for anything except the part.  No idea how they stay in business.

Decided to drop it off at the local Skoda garage (Sighthill, Edinburgh) for a £70 diagnostic check while I was over in Germany for a week.  Got a message from them while I was there saying that there was a faulty coil and that they could get the problem to jump cylinder (which neither I nor the local garage could get to happen).  They got compression readings of 12-14-14 so I authorised them to replace the coil (£85).  By this point I was missing ebay parts but genuine OEM should stand me in good stead.  Anyway, problem solved.  Car runs perfectly.

 

Is the low compression an indicator of worse to come though?  I've heard of faulty injectors causing burnt exhaust valves.  Skoda charges £1200 for the head change complete including all parts and labour (including a new Cat as the old one is reckoned to always be contaminated).  

[Rooted]

If you are having problems best go and see proper qualified and competent technicians, may i suggest.

http://autohausedinburgh.co.uk

[xman]

Is the low compression an indicator of worse to come though?  I've heard of faulty injectors causing burnt exhaust valves.  Skoda charges £1200 for the head change complete including all parts and labour (including a new Cat as the old one is reckoned to always be contaminated).  

 

 

No. Compression readings can easily vary 20% or more, and depend on equipment and technique. Nothing to worry about.

 

I know its too late, but for others with the HTP engine , I've found once a coil goes , its pretty much down and out and the engine runs like sh*te. As they cost £25 for a Bosch part from GSF, its often just cheaper to buy and replace than rely on garages to bleed your wallet. Simple process of substitution and swaps until the misfire disappears.

 

Note that misfire errors dont clear straight away, unless you do it manually via vcds. It takes several starts, several miles and maybe some time too before the ecu decides its safe to forget the fault and clear the MIL lamp.

 

Doubt very much there was anything wrong with the injector and valve problems on this engine are usually lubrication related, down to low oil flow often down to neglected oil changes that allow valve stems to wear and subsequently seats dont seal and become burnt.

Edited 18 April, 2015 by xman

[arobertson]

xman; thanks for the reply, I'm driving the car like it's fine and glad to have it back, ie not planning on ditching it and running away.  I suspect with a bit of an Italian tune up, any carbon type carp around valves could be cleared.  Todays trip to B&Q certainly loaded the engine quite heavily and full use was made of the RPMs...  I do like the sound of a hard worked three cylinder engine even if it doesn't rev quite as highly as the Smarts.  At least it won't also consume a turbo every 30,000 miles.  I got quite familiar with a lots of the guts of the Smart car over the last ten years.

 

On the fault and diagnosis; the fault was always cleared using VCDS but I find it a narking that I couldn't get the fault to jump cylinder indicating a coil fault during testing here.  The first thing I did was to do coil swaps as it's so easy.  Comparing with the Smart where coil swaps involve removing crash structures and mining in dark spaces.

 

goneoffSKi; I'll check out http://autohausedinburgh.co.uk when I get any more issues that I can't resolve in a timely manner.  Thanks.