Hello new member here, I've joined up in the hope that someone can help me troubleshoot / diagnose the problem with my polo. For a few weeks it has intermittently failed to start and only turns over. Normally after trying several times it fires up and seems to run fine when it's going. It's never cut out while running. A couple of weeks ago I drove it for around 20 minutes, came back about an hour later and it wouldn't start after multiple attempts and had to be towed home by the RAC and hasn't started since.

I've borrowed VCDS off a friend hopeing this would point me in the right direction. It came up with a couple of error codes as follows:

1 Fault Found:
18058 - Powertrain Data Bus
P1650 - 35-10 - Missing Message from Instrument Cluster - Intermittent
Readiness: 0000 0100

2 Faults Found:
01039 - Coolant Temperature Sensor (G2)
30-10 - Open or Short to Plus - Intermittent
01315 - Transmission Control Module
49-10 - No Communications - Intermittent

The coolant temp gauge has been a bit haywire of late, reading all over the place, although the car seems to have been running fine, but this error code could be the reason. I have replaced the green coolant temp sensor with a genuine VW item as I had read that this could potentially prevent the car from starting. Even if it isn't teh main cause, it sounds like it needed replaced anyway. Still no joy though after fitting this, the car just turns over but dones't fire up. The battery has gone flat which could explain the no comms errors stored I guess.

I've removed a spark plug and after trying to start the car the tip is slightly wet - plus you can hear the fuel pump prime with ignition on, so I think fuel side is ok. However when holding the spark plug in the lead with some pliers it is clear that there is no spark. So i'm guessing possibly either coil or hall sender? But there are no error codes relating to these. The engine management light hasn't come on at any time either.

I don't have a Haynes manual but have tested things on cars over the years with a multi meter, but I'm not sure how to test/rule out the coil or what to test next? Can anyone help? Thanks in advance

Edited 26 February, 201511 yr by Scoff

First Welcome to the forum.

I would first delete those fault codes as they might of been there for a while, unfortunately a Haynes won't help with the wiring as for your model they don't include any engine diagrams :( However I have a copy of the dealer manual so I'd start with the basics, is there power at the coil pack pin 2 Black wire & ground on pin 4 Brown wire, The camshaft sensor should have 5volts on pin 1 Green/Lilac wire Have you tried all plug leads as it might be a duff lead on the one you tried?

Hi Nige, thanks very much for taking the time to reply, much appreciated

I'll certainly clear the codes next now that the new temp sensor is fitted and so it will be starting with a clean slate, and the battery is fully charged up now too.

I was thinking of picking up a Haynes manual purely just for this purpose so thanks for the heads up with that. I will test those things you have listed and report back with findings - when checking for power at the coil and camshaft sensor, is that just with ignition switched on, or while cranking over? Thanks, Scott

It sounds a little like when my coil pack failed. I picked up a new one from ECP (about £55). 3 allen screws later - back in action!

Check the coil pack carefully for hairline cracks which apparently can be repaired with epoxy in the casing.

Good luck!

PoloD.

The power should be there at all times "Ign On & cranking" I don't know why Haynes haven't included any engine wiring diagrams but they also don't include them in the 9N manual either, you can buy the copy of the dealers manuals on ebay it's called ElsaWin around £20 but it's a very large program 80+ Gb and can be a pain to install

Thanks Nige, I'll maybe have a look into the ElsaWin a bit more, initial reading suggests it can be a bit tricky to install and use, but I think I'll give it a go.

UPDATE: So after some further testing this is the latest. I checked for +12v at pin2 (black wire) on the coil connector and getting good voltage there constantly with ignition on. Wiggled the wiring going to the plug while checking and get a constant 12.3 volts approx, so the coil is getting power fine. I also checked the brown cable pin 4 is getting a good earth and again after wiggling the wiring around it's definitely making a good earth connection.

Next I checked each of the 3 remaining spark plugs and oddly I was getting a spark from all 3! Out of curiosity I checked the first plug again and low and behold I was getting a spark there too!

Put them all back in and tried starting and it fired up straight away :) The only thing different is that the coil had been unplugged and plugged back in, although I had already done this a couple of times prior to this testing so I'm not convinced it was simply a bad connection with the plug. Left the car running for 20 minutes, stopped and started it about 5 times afterwards trouble free. Was about to claim victory, although slightly unconvinced as I hadn't changed anything - tried starting it again and NOTHING, just turned over yet again, and no spark from any of the plugs :( Checked the coil plug and still getting a good 12v reading even when the car was not starting. So intermittent problem somewhere, but does this sound like a coil starting to die and intermittently just not giving any spark? Or could it still be something else intermittently causing the fault.

I know intermittent faults are always difficult to diagnose. Is it worth checking the wiring and the 5v reading at the camshaft sensor next or is there anything I can actually test on the coil itself first?

There are some checks you can do on the coil pack, if you remove the ignition amp from the front of the pack, ( remove the three mounting bolts, then squeeze the two tabs at the edge of the ribbed bit, they are holding it onto the main coil) There are 3 pins from the amp to the coil, on the receptacles on the coil measure the resistance between the centre pin to the other two, it should be 0.3 ohms & while the amp is off measure the coil outputs between plugs 1 & 4 then 2 & 3 they should read 4~6 Kilo Ohms, Then on the main connector for the coil pack meter on volts between pin 1 & Ground & pin 3 & Ground you should get a pulsed 12v as you crank it over, On the Cam sensor if you can get into the back of the connector between pins 2 & 3 you should get 5 + V as you crank it.

Just looking at my spare pack, I wouldn't mind betting on a poor connection between the amp & the coil as mine were cruddy as anything !

Do you know what your engine code is? First three letters on your V5 logbook for the engine serial number as it might be the crank sensor that's causing the intermittent problems ?

Hi sorry it's taken a while to reply, I've only just managed to do some testing. Thanks again Nige, would be totally stuck without your help and instructions! Ok so I've cleared all fault codes to start with a clean slate. I'm still getting 12v with ignition on At pin 2 of the coil connector.

I checked while cranking and between both pins 1 and ground, and 3 and ground of the coil connector I'm only getting 0.03v on each, and not the pulsed 12v as suggested, so something's wrong there for a start?

I then checked the cam sensor but cant back probe pins 2 and 3 due to the insulation, so I could only test this with the cam sensor unplugged. While cranking, the voltage between pins 2 and 3 goes up to about 10v initially then drops to about 8v. After finishing cranking and ignition off, this voltage reading stays around 10v for about 20 seconds then drops to 0.04v.

Does this sound right? Not the 5v A's suggested but not sure if that's because I'm measuring the cam sensor unplugged?

I picked up a known good second hand coil locally very cheap and all the resistance measurements were spot on other than getting 0.8 ohms rather than 0.3 ohms between Centre pin and the other two, contacts were all nice and clean too. Unfortunately didn't make any difference, still no start :(

I'll grab the engine code and check the history but have a feeling the crank sensor was replaced by a garage about 3 years ago due to similar issues but not as severe. I'm going to run another vagcom scan too after this testing, just to see if anything new has come up since clearing and trying to start it several times and report back.

My engine code is AUD. I've run a new scan and the only module that has any error codes is at address 17 - Instruments, which is the KombiInstrument TRW V08

2 Faults found

01314 - Engine Control Module

49-10 - No communications - Intermittent

01315 - Transmission Control Module

49-10 - No communications - Intermittent

I've checked both connections from the main wiring loom to the ECU and disconnected and reconnected them to make sure they are getting a good connection, and all the pins look clean and no corrosion I can see. I'm starting to wonder if this could be a problem in the wiring loom in the engine bay somewhere, perhaps something is shorting out somewhere if some insulation has worn through, so I'm going to try and check as much of the loom as I can get to in the meantime to see if I can at least rule that out.

There is a polo 6n2 being broken locally to me so I might try and pick up the crank sensor before it goes just in case it does turn out to be a bad sensor at fault, I thought it would have been throwing a code if it was down to a bad sensor though?

Did you get this sorted mate?

 

My son's car has exactly the same symptoms, although runs intermittently, cuts out and won't start.

Sorry i never came back and updated this thread. The problem turned out to be a bad ignition switch in the end - i was able to test swapping this over from a known running car and this resolved the issue completely. I'm not sure if the above test results would point to this as the culprit normally, but it certainly didn't seem obvious that this was the cause. Car never failed to start after replacing the ignition switch.

Dave - sounds very similar so i'd maybe go through the tests that Nige kindly suggested above and if it all checks out, see if you can swap out the ignition switch, providing you've already tried other things and not had any success. You may not have the same problem but could be worth a try.