Diagnostics Query

[DesG]

Hello

I posted yesterday about a breakdown I had at traffic lights. Essentially, my engine had stopped on auto-stop and then failed to restart when I took my foot off the brake - it turned over and coughed a little but failed to run. A couple of technicians were passing and were kind enough to plug their kit into my engine. The guys diagnosed an EGR problem which they said was causing the engine not to start. They then cleared the fault and sure enough the engine started when I next tried. I'm still a little confused by this, would an ECU fault like that really stop the engine from running, and would a s/w reset then allow it to start, or would it have restarted anyway after a short rest. It sounds odd to me but maybe I'm over suspicious. The guys showed me a screen shot of the fault which I attach below. They also showed me a shot after their reset, which I also attach. No reason to think they guys aren't genuine, and the VIN No is correct on the shots.

Could someone who understands these things shed some light on this?

Many Thanks
Des



BEFORE




AFTER

 

[DesG]

Sorry - wrong AFTER image - should be:-

View attachment 168753

 

[Grim Reaper]

The TPS circuit fault could also have something to do with it.

 

[DesG]

The TPS circuit fault could also have something to do with it.

Thanks for the response.

I'm far from an expert, but it does sound like a likely culprit given the engine had been running fine and the fault seemed to be restart related - and once the engine started again it continued just fine with no obvious loss of performance. I didn't see any obvious warning on the dash whilst I was trying to restart using the accelerator pedal - did I mention it's an automatic. It's hard to believe the Engine Management System would prevent a restart due to a fault, but still turn the engine over when I moved my foot from the brake to the accelerator. For most faults, I thought the EMS would just the system into limp home mode. Is it possible to tell from the first image (the one before the faults have been cleared) that my vehicle had gone into "limp home" mode?

Btw, do you know if a restart after an auto stop/start pulls from the main battery or a condenser - I've been told the latter.

Will try to get the vehicle to my local VW van dealer tomorrow.

Thanks again
Des

 

[Grim Reaper]

The starter battery is the only reservoir for power on the van, there is no 'condenser' (or capacitor) fitted, I'd love to talk to the person who told you that!
VCDS (or VW's own system) should be able to give you a snapshot of the status of the relevant systems at the time of the fault.

 

[mmi]

All the faults have status of "passive" which means the fault was not "ON" when the log was read. Thus, no dash lights nor abnormal engine operation.

Anyways, difficult to imagine how fault P046C00 would prevent engine starting - basically it's just EGR valve was not in commanded position.

However, P012100 (Throttle Position Sensor, implausible signal) is an interesting one. Among other things throttle flap is used to stop engine "softly" thus it was fully closed when engine shut off - but normally returns immediately fully open for the next start. Closed flap would definitely prevent engine starting - no air into engine. But you mentioned this fault was not there after failed starting...

Any service done recently - timing belt?

 

[DesG]

All the faults have status of "passive" which means the fault was not "ON" when the log was read. Thus, no dash lights nor abnormal engine operation.

Anyways, difficult to imagine how fault P046C00 would prevent engine starting - basically it's just EGR valve was not in commanded position.

However, P012100 (Throttle Position Sensor, implausible signal) is an interesting one. Among other things throttle flap is used to stop engine "softly" thus it was fully closed when engine shut off - but normally returns immediately fully open for the next start. Closed flap would definitely prevent engine starting - no air into engine. But you mentioned this fault was not there after failed starting...

Any service done recently - timing belt?

Hi Thanks for the response...

Yes, there is an embarrassing build up to this issue, which common sense says must be related even though it's not obvious (at least to me) how.
On Friday morning I'd absentmindedly poured about 200ml of Adblue into my full diesel tank - a couple of glugs before I woke up from my heat induced doze. Refilled the Adblue dozens of times before and never done this - it was hot, and who decided to put the fillers for two radically different tanks next to each other anyway. Did a poll of every mechanic, engineer and general know-all that I knew and got various response ranging from, ignore it to don't even think of starting your engine or even opening the drivers door before you've had your tank pumped.

So, on Saturday morning a very nice chap (really, I'm not being sarky) reluctantly came to my drive (he told me I was wasting my money) and spent over an hour sucking every last drop of liquid from the fuel tank - at least every drop he could reach with a long flexible tube; incidentally why don't they fit a drain tap? He then added 10 litres of fresh diesel along with some Wynns additive and I started up my engine which started first time and ran as sweet as ever. The guy insisted on following me to my local fuel station where I filled up and then we went our separate ways. It was on the way home when I stopped at lights that the engine stopped (on auto stop/start) as I moved my foot from accel to brake. The sudden appearance of the two local car hackers was bizarre, but after careful investigation unrelated.

Btw, the vehicle is a California Ocean 17 reg' with 37k on the clock and a full VW service history. The only warnings on the MFD are AdBlue and oil service in 200 miles. Has always run like a dream and is a beautiful vehicle to drive.

 

[Grim Reaper]

If I were you I’d consider changing the fuel filter as well in case any water has been sucked up by the pump.

 

[DesG]

If I were you I’d consider changing the fuel filter as well in case any water has been sucked up by the pump.

Thanks

It's an interesting point which I discussed at length with my tank cleaning guy during the hour or so we spent sucking £140 of Costco's finest diesel from my tank. He actually carried replacement filters for T6's but insisted that it would just be a waste of time and money in my case since I'd not started the ignition or even opened the driver's door since adding the adBlue.

The two local guys had an interesting input to the adBlue discussion. One of them reckoned that there is a local valley in the tank below the filler inlet not far from where the pump draws the fuel. This means the adBlue would probably not have dispersed fully into the tank and would hopefully have been one of the first liquids to have been sucked out. Not sure if that's baloney or not, the certainly knew how to tell a good tale! Nice guys though, can't fault them for enthusiasm.

 

[DesG]

Hello

I posted yesterday about a breakdown I had at traffic lights. Essentially, my engine had stopped on auto-stop and then failed to restart when I took my foot off the brake - it turned over and coughed a little but failed to run. A couple of technicians were passing and were kind enough to plug their kit into my engine. The guys diagnosed an EGR problem which they said was causing the engine not to start. They then cleared the fault and sure enough the engine started when I next tried. I'm still a little confused by this, would an ECU fault like that really stop the engine from running, and would a s/w reset then allow it to start, or would it have restarted anyway after a short rest. It sounds odd to me but maybe I'm over suspicious. The guys showed me a screen shot of the fault which I attach below. They also showed me a shot after their reset, which I also attach. No reason to think they guys aren't genuine, and the VIN No is correct on the shots.

Could someone who understands these things shed some light on this?

Many Thanks
Des



BEFORE

View attachment 168750


AFTER
View attachment 168754

Just a quick update on this

I picked up my vehicle from VW today. I was charged £108 for a diagnostics check that revealed no serious issues and no issues requiring immediate attention. The carbon levels in the EGR were within acceptable levels, though in the upper half. VW quoted me around £400 for a de-coke but said it wasn't really necessary until I got a dashboard warning. They also quoted a full EGR replacement at around a grand. I asked them to look at a few other items including a sliding door issue which I'm starting a fresh thread on.

I've now done almost 100 miles in the vehicle on motorways and stop-start standing traffic and it has run as perfectly as ever - not a hint of trouble. So I'm putting my original issue down to a hiccup after having my tank completely emptied - maybe some air entrained into the fuel system. Fingers crossed.