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Eric, Automotive Repair Shop Manager
Category: UK Car
Satisfied Customers: 32550
Experience:  Automotive Repair Shop Manager, Technician/JA Mentor
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T know how just answer works, but will have a go. I'm in the

Customer Question

Hi, Don't know how just answer works, but will have a go. I'm in the UK and cannot afford Audi garage charges.
I have an Audi A4 TDI 1.9, Year 2000, It's an Multitronic transmission with diesel engine. My problem is that my speedo does not work (I also have beeping oil level and pressure warnings on the instrument cluster when I start to drive, but I can live with those for now).
I have tried four different instrument clusters bought as cheap as I could off ebay and after doing the key matching I get the same problem - no speedo and oil warnings (One of the Instrument clusters I tried also had the Tacho not working.)
I used a cheap OBDB II cable and VCSD lite - there's no errors reported. I tried replacing the ABS unit, still have the same problem. I tried replacing the ECU still have the same problem.
All parts replaced were 2nd hand offa ebay - One seller assured me the speedo was working on Intrument Cluster before removal.
I hooked up ODBD cable and look at readings using VC
Submitted: 2 years ago.
Category: UK Car
Expert:  Eric replied 2 years ago.
I am sorry that you have not been helped yet. I just came online and saw your question
If your scan tool has live data feed, take for a test drive and see if speed is registering on the scan tool
If not registering, then either a faulty input or output transmission speed sensor
If it does register, and since you have gone thru so many clusters which we can rule out and replaced the ecu, then there is a short in the wiring harness between the ecu and the cluster.
Please remember to rate service using the rating page so that I may receive credit. Thanks
Customer: replied 2 years ago.
It looks like a ton of text has disappeared from my original question!
I have added a Word document that contains the whole of it.
Expert:  Eric replied 2 years ago.
Ok, you have a wiring issue between the transmission control module and ecu or between the ecu and cluster
Because these are serial data lines and shielded, you cannot actually test them with a voltmeter without damaging the ecu or tcm. All you can do is check the wiring for any obvious cuts or chafing or loose wires at connectors.
If ok, this would require a special factory breakout box to diagnose the short or open circuit in the data lines
Customer: replied 2 years ago.
Hi Eric,Using VCSD lite and looking at the "measuring blocks" of some of the modules, I get speed readings OK from the ABS Unit and the Transmission Control Unit(TCU), but speed stays at zero in the ECU and in the HVAC modules.Is it logical to assume that Wheel Sensors feed speed info into the ABS Unit. The ABS Unit then passes speed info to the TCU. From there does the speed info go to the ECU first then to the Instrument Cluster? Where is the TCU unit located so I can make a basic visual check on the connections? Hope it's easy to get to, as I said, I'm no mechanic.I thought the TCU might be under the passenger seat and have spent an hour lifting up carpet and sponging out water from the passenger foot well(was due to drain hole being gunked, now cleared), but the TCU is not here and there where no connectors/connections that could have eroded here just wires running back and forth.Thanks for talking the time, appreciated,ShabirWould it be logical to assume
Expert:  Eric replied 2 years ago.
The control module is located in front of the right front seat under the carpet in the foot well.
speed sensors send signal to abs module, then from abs module to the tcm, then to the ecm, then the cluster
Customer: replied 2 years ago.
Thanks for that info.I've just removed the tcm from the plastic container and everything is dry and clean - the connection pins all look very good, no signs of decay or moisture here.Since I have no error codes in any of the modules, I guess that problem is, as you said, the wiring between the tcm and the ecu. So there's probably no point in my trying another tcm, is there?Can I unplug both the tcm and ecu and, with a wiring diagram and a multimeter, check for a current going through from tcm to ecu on the relevant pins of the the plugs at each end?
Expert:  Eric replied 2 years ago.
You should be able to. I have looked and looked and I dont have wiring diagram or connector pinouts for this
Customer: replied 2 years ago.
I haven't found any connector pin information yet.I've been looking at some wiring diagrams - a bit complex to follow, but with regard to information going between the tcm and the ecu, is there something called a "Multi Function Switch"? Could that be at fault and where would that be located?
Expert:  Eric replied 2 years ago.
The only multi function switch I know of is the one on the steering column for lights, blinkers, wipers.
Customer: replied 2 years ago.
This link below is informative about the Multi Function Switch. The guy has a different problem to mine, but it seems a lot of information between this and the tcm and ecu. He does mention a lack of error codes on ecu and tcm that make things difficult to diagnose. link informative. I think maybe this is beyond me and close to giving up - any useful advice/guidance would be most appreciated.Thanks
Customer: replied 2 years ago.
More info here too:-
Shows corroded plug.
Expert:  Eric replied 2 years ago.
Ok, that is the transmission range switch, known in the old days as the park/neutral safety switch. First time I have heard it referred to as a multifunction switch
This tells the computer what gear the transmission is in. I dont believe that there is a correlation between it and your current issues, but let me check