Emissions light
I wrote to you in March 2017 concerning the emissions light in my Audi A3 2.0 TDI SE auto DSG (engine code BKD, gearbox HLE). You suggested that I contact you again when I know the fault codes produced by diagnostic examination. I have attached the only diagnostic information I have been able obtain through several examinations by specialists. None of these suggested a constructive approach or displayed any interest in identifying the cause of the problem.
For myself, I suspect there might be an intermittent earth or even component fault beyond the new gear selector unit – possibly the electrical/electronic components within the mechatronic unit attached to the outside of the gearbox. Before even attempting to physically investigate this area, I need to verify the theory and would appreciate your advice.
I understand there are sources offering rebuilt mechatronic units, but are they reputable and reliable? How accurately is it possible to identify suspect components within the mechatronic unit by diagnostic examination or do I need to physically detach it? What is the most reliable and affordable diagnostic scanner to obtain for this work? MG Whiting Thank you for all the relevant details and the engine and gearbox code. Let me first clear up one error which is commonly made: the EML is not an emissions light. Although it will signify problems relating to the engine which will alter the emissions, it will also illuminate due to other management problems.
The DSG gearbox fitted to your vehicle is a highly complex unit and the control system works in tandem with the engine control systems. For the unit to work effectively, it must be fully aware of the engine data. This relies on a complex set of sensors and the high speed Canbus wiring.
From the sheet you supplied (see above right), I can see the code ‘28775 0 U0103 Lost communication with gear shift module (intermittent)’, which is undoubtedly the problem. This code is saying that the control module is not communicating with the gearbox intermittently. This could be due to a number or reasons, one of which may be a faulty selector module, although this can be discounted as it has been replaced on your vehicle.
The possibilities that remain are a communication failure in the Canbus wiring network between the mechatronic unit and control unit or else a faulty shift selector locking solenoid within the gearshift lever. The mechatronic unit for the dual clutch is inside the gearbox, as are the input speed sensor and clutch temperature sender. Communication with these relies on a loom within the gearbox.
With regard to the reliability of rebuilt mechatronic units, it would depend on the guarantee given with the unit and it is not possible for me to comment on individual companies. Identifying individual components before the removal of the mechatronic unit is not a task that can be carried out without dedicated equipment held by companies that perform such testing.
For a code reader that will cover the gearbox on your Audi, you will need something like the Foxwell NT414 Pro Scan Tool, which is priced at £199. It can be purchased at this link http://bit.ly/1mwdymb, but you should check with the company before purchasing to ensure that this will cover your needs.
One very simple check that can be carried out is to test the gearlever locking solenoid (N110). This can be done by ensuring that the gearshift lever will not move unless the ignition is turned on and the brake pedal depressed. If is does, then the solenoid may be sticking or faulty, and this is the most likely cause of your unwanted management light and code.
The other external check that can be carried out would be to systematically test the Canbus wiring for continuity. Although given that the fault is intermittent, I would also recommend moving the loom while testing, to check for a possible internal connection breaking while driving.