Cruise control in 90hp 1.4TDI not working

[Peter]

My newly acquired A2 (my 50th car, my 14th Audi, my 3rd A2, my first diesel A2) has cruise control installed but it will not work. I had cruise control in my previous (petrol) A2 so know what to look for in analysing the problem.

I have checked (using VCDS) the
- sensors for clutch and brake pedals
- stalk switches: ON, OFF, cancel, +/RESUME and -/SET

Sensors and switches show their proper operation (measuring blocks 006 and 022 for diesel cars, petrol cars use 066); bits toggle as expected and so I assume the wiring to be OK.

Now there are two issues.
1) The ECU part number in VCDS does not show the additional "G" to confirm cruise control activation. I tried to activate the cruise control using login 11463. No effect. Measuring block 006 shows cruise control as activated: ON=1.0 OFF=0.0 (de-activated=255.0).

2) My ELM327 OBD dongle and the Torque app on my smartphone show the speed as 0 (speed is correctly displayed in other cars). Also the ECU shows the speed in measuring block 006 and 027 as 0 km/h.

Clearly, if the ECU "thinks" I am doing 0 mph, it will assume I am in first gear and cruise control will not work.

So the problem boils down to: why is my speed invisible to the ECU and to the OBD dongle?

Note: the 90hp TDI has no G22 speed sensor. Speed is derived from the 4 ABS sensors on the wheels, reported over the CANbus by the ABS/ESP-controller. The ECU and the instrument panel are the other controllers on this bus.
The instrument panel drives the speedometer and shows actual speed. Is it there that the 4 wheel speeds are converted to one car speed?
Does the ECU perform the same calculation to derive the car speed from the wheel speeds? Or is car speed transmitted by the instrument panel?

Any help, suggestions greatly appreciated!

 

[JIGSAW]

first place id start is in the passengers underfloor compartment , id remove the ecu and unplug the wiring conectors and give the pins and plugs a good squirt with electrical cleaner, my TDI has no speed sensor on the gearbox either and uses abs sensors, I had simular issue last year after my tdi conversion that my cruise did not work and turned out the wire that goes to ecu pin in the conector block had moved or did not have a good conection as after id taken the plug cover off to examine the pins and squirted all the pins and plugs with cleaner my cruise worked again ...

 

[Peter]

Thanks JIGSAW! I did as suggested but alas, no improvement.

IMHO the problem is in the speed not being seen by the ECU although speed information is present on the CANbus; if it weren't, the instrument cluster could not show the speed.

I would expect the CANbus to deliver speed info to the ECU. But if there is a separate wire from the instrument cluster to the ECU to deliver speed info, a wiring problem could be the cause of the cruise control not working.

Does anyone know how the ECU gets speed info? Is speed info only delivered to the ECU when cruise control is installed?

Could someone without cruise control but with VCDS please check if the ECU (VCDS 01-engine) knows the road speed:
- diesel engines: check measuring block 006 (see picture, field 4 would show 255 for "no cruise control installed")
- petrol engines: check measuring block 066

 

[Catnip64]

Peter,

I have a 2003 TDI without cruise and can confirm that Field 4 of block 006 shows a value of 255.

Field 1 of the same block is for road speed, although I didn't drive the car I'm sure that this does reflect the speed when moving.

Hope this helps.

Steve

 

[Peter]

Thank you Steve! I would expect the ECU to require speed information, whether or not cruise control is installed.

The question now becomes: why is speed not available to the ECU (and the OBD-connector).

In cars with a speed sensor, this sensor connects to the instrument cluster. The speed info is used for the speedometer and most likely distributed by the instrument cluster to the rest of the car. In the 90hp TDI the ABS/ESP-controller provides speed info per wheel (visible in VCDS) and I assume the instrument cluster converts the 4 individual wheel speeds into one car speed and uses that info as if it came from a speed sensor.

A "gateway" (integrated in the instrument cluster) interconnects the 3 CANbuses and delivers speed info to the infotainment-CANbus (for radio, navigation, ...), to the comfort-CANbus (to allow locking doors at 10 mph) and to the drivetrain-CANbus (ECU and OBD).

Per this reasoning, the gateway is the problem, not sending speed info on the drivetrain-CANbus. I will ask my Audi dealer whether the gateway can by flashed or exchanged (but they'll probably suggest a new instrument cluster, without any guarantees that this will solve the problem).

Any thoughts, comments on this approach are most welcome!

Below is a picture of the CANbus system (from Audi document)

 

[depronman]

Thanks JIGSAW! I did as suggested but alas, no improvement.

IMHO the problem is in the speed not being seen by the ECU although speed information is present on the CANbus; if it weren't, the instrument cluster could not show the speed.

I would expect the CANbus to deliver speed info to the ECU. But if there is a separate wire from the instrument cluster to the ECU to deliver speed info, a wiring problem could be the cause of the cruise control not working.

Does anyone know how the ECU gets speed info? Is speed info only delivered to the ECU when cruise control is installed?

Could someone without cruise control but with VCDS please check if the ECU (VCDS 01-engine) knows the road speed:
- diesel engines: check measuring block 006 (see picture, field 4 would show 255 for "no cruise control installed")
- petrol engines: check measuring block 066

View attachment 26821

I have not just specifically checked this, but I had VCDS connected to my TDI a few months ago when diagnosing a low temp reading, I was flicking through the various measurement blocks under the engine control unit and did definitely see the road speed being displayed in kph (not MPH) if memory serves

 

[JIGSAW]

I Retrofitted my sons TDi today with Cruise so took a few photos
Before,


Activation


Activated


Silly question but have you tried going to login and re activating cruise control

 

[Peter]

Thanks guys!

Yes, I did try de-activation and subsequent activation. No effect. My picture in post #3 shows cruise control activated and ON (JIGSAW's last picture: activated and OFF). I believe the instrument cluster is not 100% working: speedometer is fine, speed is available to infotainment-CANbus (radio can display speed), speed is available on the comfort-CANbus (the doors lock at 10mph) but ECU and OBD-connector have no speed info. In fact the ECU sometimes complains with fault P0501 speed sensor signal implausibe. And rightly so!

I was at the Audi dealer today (picking up keys for my now detachable towbar) and I had a brief chat with the main mechanic. My problem was new to him. They cannot flash the instrument cluster. If the problem is in the instrument cluster, it would have to be replaced. I'll start monitoring eBay for a replacement cluster (8Z0 920 900 T) - I see zillions of cheap clusters, but those are the wrong model...

To be continued.

 

[timmus]

My problem was new to him.

Hi Peter,

I've been following your thread with some interest. When I first read the title, I thought "Oh, that'll probably be something quite straightforward", but it seems not. Like your man at Audi, this problem is new to me, too. I must compliment you on your thorough and methodical diagnostic process as well as your ongoing description of the problem and the information you've gathered so far. You provide all the information needed and nothing beyond.

From what I've gathered from reading the pages of A2OC over many years, both dealerships and independent garages can be too inclined to blame major expensive components before they've done their homework. In your case, though, I could actually believe it. You've ruled out so many other options that there are few remaining things at which to point the finger.

However, I'm doubtful that the instrument cluster is the cause of the problem. As you rightly say, the ABS unit is responsible for broadcasting vehicle speed on the Drive CAN (by doing as you've suggested; taking an average of the individual wheel speeds). It is clearly doing its job properly as you're able to read the associated measuring blocks in VCDS and the instrument cluster is evidently receiving the information. However, the engine management unit (which I'll refer to as the ECU from now on) isn't receiving the information.

The instrument cluster acts as the CAN gateway, allowing information from one CAN bus to be relayed onto another CAN bus. Again, you've provided the evidence that the cluster is doing this job properly too, as vehicle speed data exists on the Infotainment CAN and the Convenience CAN. However, the cluster plays no role in the ECU receiving vehicle speed information because the ECU already resides on the same CAN bus as the source of that information (the ABS unit). The ABS unit broadcasts speed info on the Drive CAN, meaning any other unit on the Drive CAN ought to be able to read it. Each unit on a given CAN bus is an equal node; no one unit is the host, nor does one unit communicate specifically with another. Whilst the cluster might act as the data interchange between various independent busses, it isn't the master of any. In short, if you could drive your car around without the instrument cluster connected, the ECU should still receive the signal broadcast by the ABS unit due to them residing on the same bus.

So, my finger points at your ECU. You said in your first post that measuring block 006 shows that cruise control is enabled, yet the additional G that ought to appear as part of the ECU part number does not show. That's peculiar and suggests something internally isn't right. Furthermore, whilst I don't know specifically how the Torque app works, I doubt it resides as a node on the CAN network but instead is programmed to read measuring blocks. As such, rather than it picking up speed information directly from what the ABS unit broadcast on the bus, it'll be reading ECU measuring block 006 or 027. So, it would appear to me that the ECU has some sort of software fault that's causing bizarre behaviour, notably an inability to read at least some data that it needs. The ECU needs to read a vehicle speed of 30km/h or more in order for cruise control to work.

My suspicion is that some minor corruption has occured. I've not encountered this before with an A2 engine management unit, though I've known it happen to instrument clusters. Flashing the clusters usually solves the problem as there's no hardware fault. If my diagnosis is correct, I suspect flashing your ECU should do the trick.

I hope this helps.

Cheers,

Tom

 

[Peter]

Thanks Tom, for your extensive reaction!

I can easily follow your initial reasoning: when I bought this car a month ago with the cruise control not working (resulting in a €100 discount ), I thought "Ah, clutch pedal sensor, or stalk switches. I'll have that sorted in a few minutes".

It proved to be a bit more challenging...

I have considered blaming the ECU but the fact that the OBD-connector has no speed info either and seems to receive speed from the instrument cluster, shifted my attention to the gateway. But as you suggest, the Torque app may very well request info from the ECU...

Swapping the ECU or flashing the current ECU will be the next step indeed! This may take a few days to arrange, but I will certainly let you (all) know what the results are.

Thanks again, best regards,
Peter

 

[depronman]

Peter,
I'm note sure of the age of your TDI, but assuming it is the AML 75bhp engine I have both standard maps and tuned maps available. Ideally let me know the software version that your ECU is using.
edit - I have just re read all of the post and now see that your engine is the 90bhp model, therefore sorry I don't have any maps for that ECU - appologies

 

[spike]

Just had a quick check of the wiring diagms and it appears the original speed signal wire from the gearbox was replaced by a direct connection to the ABS unit on later cars. This would suggest the speedo signal is not reliant on the canbus

There are also CAN H&L wired from the ABS unit, via the steering angle sensor to the instrument cluster and separate CAN H&L wires run direct from the instrument cluster to the engine ECU.

Cheers Spike

 

[Peter]

Thanks Spike!

I am 100% convinced that speed info is present on the CANbus. I don't have a CANbus sniffer yet (plan to build one), but I have seen Youtube demos (using Strawberry Pi / Arduino with CANbus shield hardware) moving the speedo using CANbus messages. That said, you may well be right that the wire that used to run from the instrument cluster to the G22 sensor is now routed to the ABS unit. This assumes the ABS unit is producing pulses in exactly the way the G22 sensor did. This makes sense as the wire was in the loom anyway and the instrument cluster would not need reprogramming. And the ABS unit was replaced by the newer MK60 model...

The ABS unit produces speed info per wheel and transmits these data over the CANbus. Speed related messages are defined in the CAN protocols. The picture below shows a few messages that the ABS unit transmits. Note the individual wheel speeds in message 4A0 and the car speed in 5A0 byte1 and byte2, which states "Tachoanzeige" (= speedo display) and is expressed in 15 bits of 0,002 rps which represents 0...65 revolutions/second (0..250 mph)


The idea of a bus is to reduce wiring, so all nodes sit on the same set of wires (CAN-H and CAN-L). In particular the powertrain-CANbus demands a direct connection between ECU and ABS unit. I would therefore assume the CAN-H and CAN-L wires from the ABS unit are directly connected to the CAN-wires from the ECU, even though the wires may be routed via the steering angle sensor and the instrument cluster (and most likely also the power steering control unit) as a consequence of the actual location of the devices in the car.

You did give me some food for thought, but my hypothesis that the ECU is the culprit remains.

Cheers,
Peter

 

[timmus]

Just had a quick check of the wiring diagrams and it appears the original speed signal wire from the gearbox was replaced by a direct connection to the ABS unit on later cars. This would suggest the speedo signal is not reliant on the canbus.

Well spotted, Spike. This wire must serve a purpose, so has caused me to do a bit of further investigation...

I went to my car (a 2002 AMF-based TDI75 with the MK20 ABS unit and a speedo drive fitted to the gearbox) and disconnected the speedo drive from the gearbox. If you know where it is, you can disconnect it by feel from above. Surely enough, as I drove along, the instrument cluster needle didn't move at all. Cruise control also wouldn't work and ECU measuring blocks 006 and 027 didn't register a vehicle speed. Using VCDS, I read the signal from the ABS wheel speed sensors; everything was working just fine. So far, all observations concur with my understanding.
So, I then fitted a TDI90 instrument cluster to my car. Exactly the same thing happened: with the speedo drive connected, everything was fine, but with the speedo drive disconnected, the cluster and the ECU registered no speed. This is a huge piece of evidence, because it suggests that the later cluster doesn't read its speed over CAN but instead expects a pulse-based input just like earlier clusters. It therefore follows that, no matter what the car's model year, the instrument cluster is responsible for receiving a pulse-based speed input (either from the gearbox or from the ABS unit), translating it into a CAN message and broadcasting that message on all CAN busses. All observations now do not concur with my previous understanding!

So, back to Peter's issue...
The instrument cluster is blatantly getting a pulse-based speed signal from the ABS unit via the wire Spike mentions. That wire is therefore working perfectly. The cluster is happily translating that signal into a CAN message because it can be found on various CAN busses. So, once again, my finger points at the ECU for not reading that message. The fact that the additional G refuses to appear in the part number once cruise control is enabled further suggests that's where the issue lies.

This discovery suggest there are a number of falsehoods in my previous post. Firstly, the ABS unit does not broadcast an average of the wheel speeds over CAN but instead outputs speed as an old-fashioned pulse-based signal. Secondly, the instrument cluster is much more pivotal than I had thought and suggested. The ECU would not receive vehicle speed information without the cluster connected, contrary to what I had said.

However, this discovery has further implications, albeit unrelated to this particular problem. Imagine you wanted to fit a 6-speed MYP gearbox (which doesn't have a speedo drive) to a car that uses one. I had always assumed that later clusters picked up their signal from the ABS unit over CAN. That's clearly not the case. So, to fit an MYP gearbox, the cluster must get its pulse-based signal from the ABS unit. The later MK60 ABS unit clearly has such an output, but it now seems likely that the earlier MK20 ABS unit doesn't, which would explain why it's fitted in conjunction with a gearbox speedo drive. So, whilst I previously believed that cluster generation was the key determining factor in whether or not an MYP gearbox could be fitted to a particular A2, it now seems that ABS unit generation is actually the key determining factor. I've now got some other threads to update!

Spike, well done and thank you for going back and checking the wiring diagrams. Between us it seems we've opened a can of worms. However, our understanding of our cars advances.

Cheers,

Tom

 

[Peter]

My own can of worms continues to surprise me... the story continues.

Today we swapped the ECU. An old 045 906 019 AE box was flashed with the correct (for the ATL) 045 906 019 F software (without immobiliser). I did a test drive: still no cruise control.

The guy I visited installed cruise control in my former petrol A2 and this morning installed cruise control in my son's A2. He has done tens of installations and knows his way around an A2. And has no clue where the problem can be in my current A2.

The ECU being no longer the prime suspect changes the focus to the instrument panel. The gateway in the panel connects the 3 CANbusses. It has the speed info from the ABS unit / speed sensor and distributes it to drivetrain, infotainment and comfort CANbusses.

I assume the ABS unit will not complain about speed info missing on the drivetrain-CANbus. The ECU does complain: it once more generated P0501 (speed signal implausible), which suggests the ECU sees speed info and complains about it being 0 all te time.

So I borrowed an Audi TT instrument cluster and took the newly programmed ECU (without immo) home for a test with a different gateway in the coming days.

 

[timmus]

The ECU being no longer the prime suspect changes the focus to the instrument panel. The gateway in the panel connects the 3 CANbusses. It has the speed info from the ABS unit / speed sensor and distributes it to drivetrain, infotainment and comfort CANbusses.

I assume the ABS unit will not complain about speed info missing on the drivetrain-CANbus. The ECU does complain: it once more generated P0501 (speed signal implausible), which suggests the ECU sees speed info and complains about it being 0 all the time.

So I borrowed an Audi TT instrument cluster and took the newly programmed ECU (without immo) home for a test with a different gateway in the coming days.

Hi Peter,

I agree. The finger now points back at the instrument cluster or a wiring problem.

I think you're right to assume that the ABS unit won't complain about speed info missing from the drive CAN because it can harvest that information itself from the individual wheel sensors.

Have you checked the drive CAN wiring at the instrument cluster and at the ECU? It may be that the instrument cluster is doing its job just fine and broadcasting on all CAN busses but that the signal simply doesn't reach the ECU because of a wiring problem. It would be worth checking for continuity.

Cheers,

Tom

 

[Peter]

Thanks Tom - continuity is absolutely an issue to check. I will do so once the instrument cluster is out.

From Spike (post#12) we know that separate CAN wiring goes to
1) the ECU
2) the ABS unit via steering angle sensor
and these I'm sure are directly conected (apparently inside the instrument cluster) to create one drivetrain-CANbus.
Removing the instrument cluster could break the drivetrain-CANbus making driving without the cluster at least unsafe (no ESP, ASR, etc) or even impossible.

I have seen the ASR in action, which suggests the ABS unit and ECU communicate with each other.

I would not expect the OBD connector to be a node on the drivetrain-CANbus, so there must also be separate(?) CAN wiring running from the instrument cluster to the OBD-connector (and probably more than just CAN wiring).

Today I drove some 150 miles. Before I left home I did a VCDS AutoScan and found no errors. Upon return I did another AutoScan and now the ECU reports one error: 16885 / P0501 implausible speed sensor signal
The instrument cluster reports no error and shows the actual car speed in measuring block 1 field 1.

So the car "is aware" of a problem related to speed info... "all" we have to do is find the source of this fault code.

Rgds,
Peter

 

[Peter]

My cruise control is working!
With a TT instrument panel replacing my own 8Z0 920 900 T at last I get the speed in measuring block 006 and the cruise control works flawlessly.

The car is not overly happy with this panel: no rev counter, a lot of beeping and complaints about oil and brakes as well as several warning lights for ASR and ABS (and the disabled immo). What's worse in the current freezing cold: climate control cannot be switched on. The radio on the other hand works as usual.

The OBD port now shows the actual speed as well (supporting the theory that it gets speed info from the ECU).

So the hunt is on for a new panel - several are offered on eBay - which will then need to be matched to the car...

 

[timmus]

Hurrah!!

That's great news, Peter. It seems there is indeed something amiss with your instrument cluster. I'm now left wondering whether there's a physical problem with your existing cluster or whether it's a software issue. I've recently repaired a cluster for a UK-based member by hunting down a software bug, so I'm wondering whether I could achieve the same with your cluster.

I can tell from the part number of your cluster that your car does not have DIS. I therefore expected a replacement to be very cheap, as non-DIS clusters sell in the UK from about £30. However, looking online, it seems that even non-DIS clusters are quite expensive in continental Europe. If you need to keep your car operational, then buying a replacement is probably the easiest option, but one way or another, I'd be keen to have a go at repairing your existing cluster.
Given that you had somebody flash your ECU recently, I'm assuming you know someone who's capable of matching a replacement cluster to your car?

...we know that separate CAN wiring goes to
1) the ECU
2) the ABS unit via steering angle sensor
and these I'm sure are directly conected (apparently inside the instrument cluster) to create one drivetrain-CANbus.
Removing the instrument cluster could break the drivetrain-CANbus making driving without the cluster at least unsafe (no ESP, ASR, etc) or even impossible.

Although this is now somewhat academic as the fault has been traced, I thought I'd comment on the above anyway...
The Audi wiring diagrams display the CAN wiring in a way that helps to communicate signal flow. However, the physical implementation of that wiring doesn't necessarily correspond to how it's drawn. The CAN wires do not go through the instrument cluster. The CAN wiring is done in a star shape, with all the wires connected together in a bullet crimp, which is then buried somewhere in the wiring loom. The instrument cluster is on one spur of the star, the ABS/ESP on another spur, the angle sensor on another spur, etc, etc.

Whilst your cruise control issue has caused some head-scratching, it's been a fun and challenging little problem. You're not the only person who's happy the problem has been found.

Cheers,

Tom

 

[Peter]

Yesterday I called a company who service instrument panels (near my home and highly recommended by my Audi dealer). He had never heard of my problem before and gave me a rough estimate of € 150 for the repair (which would have to wait until 2017 as he was quite busy).
I then knew a replacement would be both faster and cheaper and I ordered one (second hand).

It was delivered an hour ago (€ 65 + shipment and incl. 3 months warranty) and immediately installed in the car. A short test drive proved everyting OK, including cruise control.
As an additional bonus I have the old panel to experiment with, play with CANbus, upgrade to DIS, ...

Indeed the guy that flashes ECUs will match the new panel to my car and my keys and I'll also keep an extra ECU with immo disabled.