1.8T L&K unsual probs - data bus, speedo & radio

[greg123]

Hi Guys,

This is in my personal 2002 Octavia 1.8T L&K estate which is pretty mint and these faults have crept up recently, other than the speedo issue which has been with me intermittantly some time. Anyone experiencing similar faults and resolution advice appreciated.

The speedo works perfectly in an output test, right round to 150mph. When on the road it's generally fine unless hitting motorway speeds, where it starts to waver around all over the place indicating a lower and fluctuating speed than real road speed. It also seems to hit a wall at 80mph, where should you be on a test track and drive faster, the speedo drops back down as you speed up, down to 70mph sometimes, while wavering around. As soon as this 'wavering' starts, the cruise control if switched on will be erattic, indicating the speed signal to the cruise is also wavering around. I logged in and looked at the speed on vag-com and on the climatronic display, all 3 (including the speedo) say different things and seem to increasingly become 'wrong' as you get over 60mph. Up to 60mph on a fresh drive the speedo is pretty bang on. MPG and Odometer are also correct.

I have the CD player missing. I recoded it to 'no cd player' coding so the 'missing cd player' error does not come up. The radio works perfectly.

BUT and here is the strange thing. I keep getting can bus single wire errors. I can't figure the cause of the speedo issue. However I noticed something new last night. If I press the brake pedal as vag com is scanning any of the radio, can bus or instruments, it makes the dash beep and bring up 'brake light failure'. Also, if I have the side lights on when scanning any of those modules, a beep the bulb and 'lights failure' warning come up.

Also, if I'm not wrong, unless I'm pressing the brake or have the side lights on, the 'radio - no communications' error doesn't appear, I can clear it and it stays away.

Finally, the radio gets VERY loud as I speed up, uncomfortable. Not sure if this is connected but it probably doubles the volume between 10mph and 70mph.

I don't get much time to spend on the car but I managed to scan it again last night at got these faults:

Address 17: Instruments Labels: None

Part No: 1U0 920 921 H

Component: KOMBI+WEGFAHRSP VDO V08

Coding: 31412

Shop #: WSC 31480

TMBFL21U638669636 SKZ7Z0B1375544

2 Faults Found:

01336 - Data Bus for Comfort System

80-10 - Single-Wire Operation - Intermittent

01304 - Radio

49-00 - No Communications

-------------------------------------------------------------------------------

Address 19: CAN Gateway Labels: 6N0-909-901.LBL

Part No: 6N0 909 901

Component: Gateway K<->CAN 0001

Coding: 00006

Shop #: WSC 31480

3 Faults Found:

01336 - Data Bus for Comfort System

80-10 - Single-Wire Operation - Intermittent

01304 - Radio

49-00 - No Communications

01333 - Door Control Module; Rear Left (J388)

49-10 - No Communications - Intermittent

-------------------------------------------------------------------------------

Address 29: Left Light Labels: None

Part No: 1U0 941 651

Component: EVG GDL + AutoLWR 0002

Coding: 00005

Shop #: WSC 31480

2 Faults Found:

01539 - Headlights Not Adjusted

35-00 - -

65535 - Internal Control Module Memory Error

00-00 - -

-------------------------------------------------------------------------------

Address 46: Central Conv. Labels: 1C0-959-799.LBL

Part No: 1C0 959 799 B

Component: 4Q Komfortgerát HLO 0003

Coding: 00259

Shop #: WSC 31480

Part No: 1U6959802D

Component: 4Q Tõrsteuer.FS KLO 0004

Part No: 1U6959801D

Component: 4Q Tõrsteuer.BF KLO 0004

Part No: 1U0959811D

Component: 4Q Tõrsteuer.HL KLO 0004

Part No: 1U0959812D

Component: 4Q Tõrsteuer.HR KLO 0004

3 Faults Found:

01336 - Data Bus for Comfort System

80-10 - Single-Wire Operation - Intermittent

01334 - Door Control Module; Rear Right (J398)

49-10 - No Communications - Intermittent

01333 - Door Control Module; Rear Left (J388)

49-10 - No Communications - Intermittent

-------------------------------------------------------------------------------

Address 56: Radio Labels: None

Part No: 1U0 035 161 D

Component: Radio GRO 0001

Coding: 00401

Shop #: WSC 00000

1 Fault Found:

00853 - Loudspeaker(s); Rear

36-00 - Open Circuit

End --------------------------------------------------------------------------------------------------

Any thoughts appreciated,

Greg.

[fordfan]

I think that you need to check the integrity of the speed signal at its source. I know on the automatic the signal is generated from a unit on the gearbox, I am not too sure about the manual gearbox, it could be derived from the ABS system. Wherever it first comes from it will be from the powertrain, so it first needs to be checked with VAG Com in either the engine or ABS control units, it might be an idea (if you have access to one) to check it against a GPS device.

This same speed signal is then broadcast to the other systems that use it, if it is OK on the powertrain side of things and is the erratic in the other systems, it would be logical to suspect that the Gateway may be corrupting the signal in some way.

With single wire operation mode, I tend to count this as not significant as the CAN system has two wires which both convey the same data.

[greg123]

Interesting.

The auto box has a speed sensor and a road speed sensor. The speed sensor has been replaced after a fault was indicated and is now clear. I have not replaced the road speed sensor - I'm not sure how it can be faulty if it works fine up to 70mph.

As for the signal - correct me if I'm wrong, but I thought it was delivered and decoded by the instruments? And then pumped out to everything else by canbus. Meaning that a fault could still be the instruments, correct me if I'm wrong but you can't log into the gearbox direct and pull a speed signal - all speed signal delivered via the instruments right?

I have checked speed against gps, it's too low as you get higher speeds and when checking it via vag-com strange things happen, it's like the speedo is in treacle and signals are delayed, as well as too low a value as the speed increased eg reading 80kmh at 100kmh. This only seems to happen when I'm logged into the instruments looking at speed in measuring blocks.

As for single wire, yes it's supposed to work but it's a fault and so I'm aware single wire mode is a Reduced Speed Reduced Mode which I'd like to get rid of if I can as I don't know if it's causing bottlenecks if I'm trying to do two things at once.

Greg.

I think that you need to check the integrity of the speed signal at its source. I know on the automatic the signal is generated from a unit on the gearbox, I am not too sure about the manual gearbox, it could be derived from the ABS system. Wherever it first comes from it will be from the powertrain, so it first needs to be checked with VAG Com in either the engine or ABS control units, it might be an idea (if you have access to one) to check it against a GPS device.

This same speed signal is then broadcast to the other systems that use it, if it is OK on the powertrain side of things and is the erratic in the other systems, it would be logical to suspect that the Gateway may be corrupting the signal in some way.

With single wire operation mode, I tend to count this as not significant as the CAN system has two wires which both convey the same data.

[greg123]

Sorry to bump this but anyone got any ideas on where to go to get started tracing? I don't really want to rip the dash and spend £200 having it looked at to be told it's okay.

Is there anywhere in gearbox or engine I can log into to get a mph reading as fordfan suggests? I don't know of anywhere.

Greg.

[DGW]

If you don't get any further responses here, I will move this thread to the Diagnostics and VAG-COM forum if you wish.

[greg123]

Hi Denis,

Yes please, it's a bit of an unusual one.

Greg.