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Discussion Starter #1
I have a curious problem, more details tomorrow but I request basic information in order to trouble-shoot.

Yesterday got new batteries, dropped the car at the dealer to replace them (and a few other things like oil change, etc.). Today he called to say he's replaced batteries but the car is showing a lot of fault codes which are not clearing. In the past, faults appeared if battery voltage dropped but would clear after a good charge, or when the car was running. Now he says there are more faults than before and they are not clearing. His only suggestion is to replace all the various sensors showing faults which sounds more than a bit odd. Spoke with the service adviser, not the mechanic; hopefully the mechanic might have more sound understanding.

I'll go tomorrow and try to trouble-shoot with the mechanic.

In the meantime, does anyone have any suggestions? Could it be due to wrong sequence of battery replacement, or shorting something, etc.?
 

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hi, have you tried clearing the codes using VAG COM VCDS? normally as i know in most cases all codes are cleared after the startup and driving few meters but if any codes are in the memory they might need clearing with VCDS. and it should be gone :)
 

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Discussion Starter #3
I did not (my non Ross Com cable needs an old XP laptop...) but the dealer has the VW diagnostic tool, and he said he could not clear faults with it
 

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It might be a small but significant issue: Are they saying the faults will not clear at all, or are they saying the faults can be cleared but they come right back? In VCDS sometimes you can clear a code and VCDS confirms the fault has been cleared, but the fault quickly comes back.

Could one or both of the new batteries be bad? It happens. Maybe see if they have fresh mfg. date codes on them. Are the new batteries known for sure to be fully charged? What's the voltage with the car running and not running?
 

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Discussion Starter #5
Not sure about codes, probably coming back but I'll check and report tomorrow.
The batteries are original VW manufactured in 2nd and 3rd quarter 2015. Charge voltage, will also confirm tomorrow. Cheers.
 

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Were the batteries connected in the correct order? Rear battery is always first (connected or disconnected).

-J
 

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Discussion Starter #8
Thanks folks, indeed after a lot of clearing faults over and over, realised the mechanic sometimes hooked up the diagnostic for too long without switching on the car, running down the (new) batteries, hence more faults.

So the last two passes with engine on (battery charger was hooked to some other car), we got two different fault codes.

The first, under heading "Control Module 2 for Turbocharger Replacing" P1953 18361, Turbocharger control module 2 faulty (tbd intermittent)
this fault used to occur when old batteries ran down also. Cleared. Second time got this:
16562 P0178 Fuel Composition Sensor Circuit Low under the heading "Flexible Fuel (FF) Sensor -G133-
Took the car for a little drive, lots of white smoke, tried clearing the fault, but did not go away (nor the white smoke).
I've left the car with the dealer for the weekend (needs suspension work). Hopefully after suspension work is done (and codes relating to ride height self learning cleared), this will also go away.

Any advice? Didn't know flexi fuel sensors were used in Diesel cars. Tried looking for it here and on Ross-Tech; here only one person had problem which was resolved with switching two identical sockets (other one for coolant temperature). I don't think that's my problem. No answer on Ross-Tech forums.

Where is this senor located?
 

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That sounds like a false code to me.

How about the complete autoscan of the truck? I'd suggest doing it with a battery charger hooked up ;)

-J
 

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Were the batteries connected in the correct order? Rear battery is always first (connected or disconnected).

-J
x2
Bentley has dire warnings about damage because of this. Only applies to early V10.
 

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Thankfully when I hooked mine up wrong it didn't damage anything, the kessy module simply didn't boot up and trapped the key in the ignition lock.

-J
 

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Discussion Starter #12
Back with newer, stranger problem (electric):
So replaced batteries (both), with new VW (Varta) batteries, manufactured in 2nd and 3rd quarter 2015. Took mechanic some time to clear codes because he was letting batteries run down (not connecting to charger while doing diagnostic with VAS 5052 factory diagnostic). I'm afraid he also did not charge the batteries before installing.
Finally though, charged (through terminal in the engine bay) and cleared all faults -- related to turbocharger control module, air compressor temperature sensor, once flexi-fuel sensor and random others which would go away -- convenience system).

Now, after two days of not driving, noticed battery was between 12.5 and 13V (on the dash gauge) before starting.
Also after starting it remains always just a sliver under 14V constantly.
But the strangest: hooked up my vag-com cable (non ross-tech but registered), cleared turbo charger control module faults. But had to reset these every time I stopped the car for more than 10-15 minutes (voltage stil reading above 13V before starting). And strangest still, while driving I noticed the car was out of power, stopped, connected vag-com, turbo-charger control module fault had re-appeared (while driving, was fine for the first 20 or so minutes after starting the car but appeared suddenly). Cleared it with vag-com, went away, drove home (no power issues). Parked. Worried.

Previously (with old, faulty batteries) the turbo-charger control module faults would only come if the battery voltage dipped below 12.5V before starting but NOW they're appearing 1) after re-start (not every time) even when voltage is above 13 and 2) while driving.

I'll take the battery covers off myself to see if they're properly connected, fuses haven't blown, or the disconnector switch of the front battery. But can't test other things (like relays, control modules, etc.)

A word on the mechanics: it's at an old VW dealership--were active since 1950s, but the dealership has recently been bought by some private business who have not yet paid VW their royalties so not officially accredited for a few months. But the mechanics are trained by VW. Generally OK (and exceptionally careful which is good) but not the sharpest for trouble-shooting. There are three other V-10s in town, dozens of Touaregs, Q7s and Cayennes. They all get their cars fixed at this ex-dealership, so no shortage of experience but I still feel I need to guide them through everything (took 4 days to change front air-suspension struts for example).

Any help/ advice/ technical information will be greatly appreciated.
 

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Discussion Starter #13
Oh and one more thing: the "fault running gear" warning also came back after battery replacement and two days of not driving--when I switched on the car (before start). Fault is level settings not learnt.

To make it simple:
1. Before replacing battery had random faults including "turbo charger control module #2" ONLY if battery dipped below 12.5
2. After replacing batteries all faults gone on first day.
3. Two days later (not starting), battery was at 12.7 or 12.8, "running gear" and turbocharger control module #2" faults.
4. Cleared turbocharger fualt, drove. Restarting after 15-20 mins, noticed car slow, checked, turbocharger fault returned but this time control module 1 and 2. Cleared.
5. Once while driving, loss of power, checked with VCDS, faults relating to turbocharger control module 1 and 2 had returned. Cleared, drove home. Parked. Sent message.

Other details
- voltage when driving is a sliver under 14.
- Mechanic said (and showed on ELSA that he's correct) he removed front battery first.
 

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Discussion Starter #14
UPDATE--found two faults:
1. current leak due to faulty Kessy module--replaced the two MOSFETs and six resistors as advised on the interwebz--less serious but problem persisted.
2. Had a couple of bad reverse sensors (got crushed in a bumper bump)--it makes no sense to me but after replacing these two, all electric faults disappeared as if by magic (ok not all, I still have two faulty door unlock buttons which I've been told drain battery but not nearly as bad as before--can leave car parked for four days without serious drain; on fifth day it shows load intervention).

Thanks all for your help.
 
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