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[1.4 AUA] Electrical problem injection/ignition: Help please from France

Philippe Holland

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Dear German A2 friends,

This is my first posting here, as Bret recommended I ask your advice.

I have a long ongoing problem with my A2 1.4 petrol.

I would be most grateful if you could give me some advice.

Below is my last post on the A2OC website on the subject:


My Audi A2 has now been with my local Audi dealer for 7 months and they cannot find the problem. They are honestly trying their best.

Each time I visit them I am now hoping to hear that the car has fallen off the ramp and is destroyed or it has caught on fire...

Just to recap very briefly the problem.

Car starts fine....if left ticking over, after about 3 minutes....a slight misfire starts on No.2 cylinder (it is always No.2)

30 seconds later, the EML comes on and there is no more injection signal and the car runs on three cylinders.

Clearing the fault code whilst the engine is running restores it to four cylinders again until the misfire starts again and the ECU cuts the signal to the injector.

If you start the car and drive immediately away, it will mostly run fine, until you come to a set of lights and again after a few moments at tick-over, it will revert to three cylinders.

Turning off the engine, waiting half an hour will make it run on four again.

I have and the dealer have done the following:

- Replaced both lambda sensors, all the engine sensors bar the knock sensor.

- Cleaned the Air flow meter and the EGR valve

- Had tested and then checked with another ECU, the ECU

- Ran a parallel set of wires from the ECU to No.2 injector

- Replaced the injector

- Replaced all plugs, wires and the ignition module

- Removed the head, checked all valves and cam gear (head has done 5000kms)

This car is now on it's third head and tracing the history shows that it has been having problems since 2008 at 70,000kms.

We are trying another ignition module as we think that a poor spark on number two cylinder is making the ecu cut the signal.

We are all at our wits end. I bought the car for my wife who...let's just say, is less than impressed....


Can anyone tell me if the knock sensor can pick up a misfire on a single cylinder and instruct the ECU to cut the signal to that cylinder?

I can imagine the injector signal being cut to avoid bore wash if something else was playing up.


As a reminder, the car is a bog standard, nice and simple 1.4 petrol with the AUA engine.

My only other thought is a resistance building up in the harness from the ECU to the ignition module on number 2 cylinder causing a poor or delayed spark, thus effecting the combustion, thus causing the ECU to cut the injector signal.


Truly gutted by this car.


Any pointers more than gratefully appreciated.



The first post can be found here:

1.4 petrol low compression or dealer fast-one?


Thank you everyone for your help and apologies for making you read this in English

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The knock-sensor G61 gives only a universal signal, but it is used in combination with the Hall-Sensor G40 signal (position of cam-shaft) to identify a specific cylinder causing problems. So think of them of a pair, when checking for causes.


The AUA ignition always ignite 2 plugs at the same time (because the module has only 2 amplifiers) , 1+4 and 2+3. Just as an info for further checking or changing parts positions.... (one ignition is used, the other is wasted while at outlet-stroke)


Although not really a candidate for specific cylinder probs, but the combined temp-sensor (G2/G62) can cause problems, when producing jumping signals


Well, since you changed already almost everything and have a clear view on the diagnostic messages, also surely checked the camshaft tolerances, there is not much left... Checking the basics according to specs, like timing belts positions and proper function of adjusting rollers, logging data from sensors for drop outs, compression, petrol pressure and regulating valve... You certainly have the right ecu type ...-Q, or ...-EG numbering? And nobody changed not dedicated parts before? Using the specified ignition plugs only?

Checked also crank-shaft sensor G28 for data and all magnetic sensors and their corresponding position markers for any polluting metal chips?


Than it might be an option to change the whole engine harness, offers on ebay e.g.

Leitungssatz Kabelbaum Motorkabelbaum 1,4 l AUA Benziner Audi A2 8Z1971072BP | eBay


Motorkabelbaum *AUA* *8Z0971072AE* / Audi A2 8Z0 1.4 16V / 00-05 112TKM | eBay


(the number of harness is to be found on that white strap inside the drivers foot compartment, the might be differences between cars with/without climatronic and be sure to get one for AUA since for BBY it is different.) The plugs for the injectors vary, but can be changed.

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I cannot judge completely from your topic on the British forum... do you have the AUA engine code with central ignition module (I guess from your first post here) or the BBY with four single pen modules?

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Yes the car is a AUA with central ignition module, which has been checked, changed and checked again.

I now believe that the problem is a bad earth between the ECU and the car.

The injector cuts out after a few minutes when ticking over. My cheap LED injector signal tester does not light up giving the impression that the signal has been lost, BUT when an oscilloscope is connected the signal is still there, but obviously not strong enough to power the injector or my tester. I presume that an oscilloscope requires very little power to be able to take a reading.

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The cylinder head+camshaft+lifters are all new.


Please be more precise with the new parts: Is also the housing of the camshaft renewed or only the shafts?

With an old housing the bearing of the camshaft can still be worn out due to oil problems before (e.g. freezing) and than a new camshaft will still run out of tolerances.

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Thank you DerWeßA2 for the link. Very interesting that all the cars in that thread were 2002 models. The problems experienced by the other owners and garages are identical to my car. I am seeing my dealer this morning and will give him a copy (thank you Google translate!)

My car has had three new cylinder heads, but I cannot see any bill for camshafts , housing or hydraulic lifters.

The oil was very black when I got the car. I wonder if the long oil change procedure was such a good thing in hindsight.

I will post progress. Thank you everyone

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seems not to be a regular part for aftermarkets .. couldn't find something, except used ones on ebay.

The housing alone is 036103473B for AUA and here at VW it costs 320E. If you have the means to check the old camshafts and lifters, it might be worth a try, so we can all learn from it :-)

(The srews of that housing shall be replaced, too). If used parts, be aware for differences of later models (BBY, or certain golf/seat/skoda models, the housing might have different sensor and ventilation connections)

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Hi Philippe,

what´s going on with your A2?


You wrote about three! new cylinderheaeds, that´s incredible.

You really should make sure if they ever changed the camshafts and the housing.


Like A2-E wrote before, there are some differences in the housing to the later models. For example the BBY has an additional ventilation connection. But you can easily close the connection, and use the BBY housing anyway.


This will give you a higher chance to get good used parts.

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Yesterday morning I delivered two new camshafts to my Audi dealer, who was very impressed by the savings I had made and very curious to know the source I got them from!

Although not wrapped in "VW" paper, they appear to be genuine parts from an original OEM supplier.

Each camshaft cost me 125€ instead of 287€ + 20% tax from Audi, a saving of 440€. I could not find a new 'old stock' housing, so will be getting one through Audi.

I ordered the camshafts by phone and got the UPS confirmation that they had been sent before I got the bill from the company. That level of service and trust would never exist here in France.

So, hopefully today, we shall see if all this work will result in the car being fixed.

A car designer by profession, I had always loved the A2 concept. So far I have driven the car 50kms and it has spent the rest of the time at the dealer.

Let's hope that this is it.

The link DerWeßA2 posted was word for word the same scenario as my car, so I am being optimistic that we have found the solution.

My A2 is also white...

Many thanks for all the support. Without you guys, I would be still turning in circles.

I will post the results shortly.


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Hello everyone,

Installing new camshafts, housing, hydraulic lifters has improved the smoothness at tick-over and the car runs well, but the fault is still there.

If you start the car from cold and left it warm up, it starts fine on four cylinders and then after a few minutes will start to misfire on cylinder 2 before the ECU cuts the signal to the injector when the car will run on three with the EML flashing.

Resetting the ECU whilst the engine is running instantly restores the car to four cylinders until it starts to misfire again and then it will cut out back to three.

If you start the car and drive it immediately without letting it idle, it drives well.

As you will see from previous posts, we have checked and changed everything.

I only have two ideas left.

I asked the garage to disconnect the knock sender and then start the car from cold. My logic was, if the knock sender was disconnected it would not pick up a misfire and hence the ECU would not cut the signal to cylinder 2.

Disconnecting the sender changed nothing.

Other thought is that there is an air leak starting in the inlet manifold as the engine warms up causing a weak mixture and misfires.

The Audi workshop manager had his head in his hands and we are all looking for a solution.

Anymore ideas out there?

Many thanks, Philippe

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As far as I understand from the handbook, misfire occurs, if the ECU cuts back the ignition to the maximum value (14°) and still senses knocks from the sensor. And it is a learning system, if for longer period misfires are sensed, new value will be used by ECU. Hence, if you cut the knock sensor for testing, the ignition may still use the limit values or even uses by default with missing sensor. And it might be necessary to force it back to normal values while testing improvements.


First is, to check the diagnostic of MSG, at what value the ignition is running.

-> 01 engine

it starts with block 11 -> Field 4 should be between 0-10° for regular ignition. if it is so, there must be other, mechanical reason than controlled cutbacks by ECU (e.g. timing configuration, mixed parts, inlet air, petrol quality ... )

block14 to 16 shows status of misfire at cylinders. (it can be zero again after smooth running in idle for more than 3 minutes)


block 22 and 23 are interesting here: in field 3 and 4 it tells the ignition cutback of each cylinder, if it is flat 14° at one or more, reasons has to be checked:

->quality of petrol, plugs, coil, knock-sensor, AGR (waste-gas-ventilation? :-) ), petrol valves, peripheral parts on engine are loosen and rattling, so the handbook tells :-)


block 28 says in field 4 about tests results of knock-prevention-system


The knock sensor plug has gold contacts and should be clear of corrosion and the sensor should be tightened to exact 20Nm, in doubt loosen and refit. AGR can be checked also with basic adjustment procedure


Last but not least, if you got the car used and it had never run fine, check the petrol quality, maybe someone put bad stuff inside, water inside or there have been mix-ups with gasoline, ethanol, what ever....

Have you checked the petrol pressure of 3 bar? The fuel pump could be faulty....


(Maybe the garage already knows all that, maybe not ....)

Edited by A2-E
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Hello everyone,

We are focusing on air leaks now and the car is being tested as I write.

On the inlet manifold there is a round access cover with an inline valve inline with number 2 cylinder. I have no idea what this does. It is part number 036129720.

Can anyone tell me what this does please?

You can see it here: AUDI A2 2000-2005 1.4 16V AUA AIR INTAKE INLET MANIFOLD P/N 036129711BH (44804A) | eBay


I am hoping the leak comes from here and is making the mixture weak and causing the misfire.

The misfire starts when the engine and lambda sensors are up to operational temperature and on 'open cycle', rather than on the 'closed loop' fixed map when the lambda sensors are not instructing the ECU to richen or weaken the mixture.

We'll see the results tomorrow....(please!)

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  • 4 months later...

Zur besseren Vergleichbarkeit: Neuer Kopf bedeutet die Nockenwellenhaube mit NW oder der Zylinderkopf mit neuen Hydros und Schlepphebeln? Oder beides?


Neuer Riemen heißt, die Einlass- und Auslassnocke stehen perfekt zueinander (Einstell-Bohrungen der oberen Zahnscheiben fluchten)?


Kompressionsmessung zeigt kein mechanisches Problem an? Benzindruck ausreichend (andere Benzinpumpe mal testen?)


Alle beteiligten elektrischen Faktoren abklopfen:

-anderen Nockenwellensensor testen

-Sitz vom Klopfsensor prüfen, lösen und wieder exakt mit 20Nm anziehen

-Widerstände der Zündkabel/Stecker vergleichen

-Zündkerzen neu und richtig?

-evtl mal eine andere Zündspule testen


Vielleicht kommen solche Effekte ja auch aus ganz anderen Ecken, Masseprobleme, AGR, etc...

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Hi Chris,

Thank you for your message. My car is now working again. The problem may have been a combination of things, but the part that finally cured the problem for was the ‘knock sensor’ on the back of the engine that detects each explosion in the cylinders.

This was the only sensor on the car that I did not change before giving up and handing the car to my local dealer….

Working in conjunction with the cam position sensor and the crankshaft position sensor, the knock sensor allows the ECU to calculate if there is a problem with one particular cylinder due to a bad detonation or if the timing needs to advance or retard.

This part has gold plated connectors and needs only to be tightened to 20Nm.

If there is a problem such as poor combustion then the ECU cuts the injector signal to that cylinder to avoid unburnt fuel washing the oil off the cylinder wall, or worse unburnt fuel making it to the catalytic convertor and ruining it.

Poor combustion can be caused by bad timing of the fuel delivery, bad timing of the ignition or incomplete combustion because the valves are not opening enough to let fuel in, or not enough to let burnt gasses out.

I have found researching the Internet that the problem with No.2 cylinder happens often.

I changed the camshafts and the cam housing as this was recommended to me to do, due to cam freeze.

It did not change the problem, but the car did run a little smoother.

The cams are made from heat treated steel and they revolve inside an aluminium housing, without any additional bearings. This is not a great engineering solution and if oil changes have been neglected then the parts can wear quickly.

My Audi dealership said they old parts were fine and actually the lobes of the cams that activate the hydraulic cam followers were perfect. However, I had nearly 1mm of vertical play in the journals where the cams turn in the housing and the journals were badly scored. At tick-over, this 1mm of vertical wear may well have caused the valves to open less than they should, hence causing the poor combustion, with the ECU then cutting the signal. At higher engine speeds with a greater centrifugal force acting on the valve mechanism the problem maybe less apparent.

The workshop manager did not want to change the knock sensor, because after a year of joint investigation he did not believe it was the problem.

I insisted he changed it and at the same time they ran a parallel set or wires from the sensor to the ECU in case there was a broken signal.

This cured the problem and the car runs fine now. If I had only changed that last sensor before handing the car over to Audi, then I may have saved myself nearly 4000€….

At least I now know that all the valve gear, cams and associated parts are now new.

I just need to keep for car for another 10 years now!

Good luck in finding the solution.

With kindest regards,


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  • 6 months later...


First of all, excuse me for my poor english.

So I have a very similar problem with a VW Polo with the same engine.

But one thing is very strange for me: If your problem was this knock sensor, why have nothing changed when you disconnected it?

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I repeat my question, since I'm not sure you have seen it, because of the server-problem:


So I have a very similar problem with a VW Polo with the same engine.

But one thing is very strange for me: If your problem was this knock sensor, why have nothing changed when you disconnected it?

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If you see a double message, we also do :D

A disconnected knock sensor will result in different failure or running modes and diagnostic messages.

You are right, it would have been interested, if that specific "2nd cylinder"-output was absent after disconnection, (what somehow would be logical) although due to new conditions and hence messages, that might not exclusively point you to the source of the old problem.

However, the specific point here was to recall, which parts are involved generating that specific failure messages, and one is that knock sensor, which is sensitive for connection and mounting but not for detection.

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  • 5 years later...
vor 22 Stunden schrieb A tighe:

Why does me A2 not start ! Then all is ok ? . Is it transponder?


If you have a problem with your transponder, then the motors starts for a brief moment but shuts down right after that.

When your A2 is not waking up at all, then its not the transponder.

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  • Nagah changed the title to [1.4 AUA] Electrical problem injection/ignition: Help please from France

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