VAG Common Failures


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    Audi A4 (1994-01)  2.5 TDi  Engine code AFB  suffer ECU output problems from ECM PIN number 17D (Air condition control module) when testing frequency should be 38hz when idling & 150hz at 3000rpm.  Should any other values be recorded, the main ECU should be suspected to be malfunctioning.  This internal ECU fault is able to be repaired.

    Audi 2.5 TDi A3 A4 A6 A8 six cylinder DOCH engine cuts out will not restart, probable cause.  Injection pump failure, internal seal.

    Audi A6 all models 97-05  common problem with horn sounding when ignition is switched on.  Fault with short circuit to earth thru steering wheel control module.  These modules can be repaired.

    New A6-A8 2002> to replace the parking brake pads you will need specific electronic equipment to wind back the brake calipers (more info@ electrical equipment advice page of this website).

    Audi A8 early models 2.8 4.2 1994> suffer auto gearbox changing problems, general consensus from the trade, is the internal gearbox oil control manifold is weak, gearbox control module could also cause same fault (we can test these).  But if fault is traced to the auto gearbox, it's going to be a very long, complex & very expensive job.  None of the auto gearbox jobs are going to be easy, but the five speed tiptronic box is the one to avoid.  I am very used to high parts prices, but quotes for parts, relating to this gearbox, even made me smart (28-01-07).  Audi V8 from '91 & A8 from '94.  018 gearbox the ATF cooler pipe connection leaks at gearbox.  The ATF cooler pipe vibrates this causes the pipe adapter at the gear box to leak. 

    VAG 1.8T Engines with AGU code.  Faultcodes for hall sensor, map sensor, & idle adaption.  Problem with loom damage.  Wiring chaffed through under battery tray, above gear change linkage, loss of 5V feed to the sensors.

    A6 all models suffer from, short cable to code-grabbing aerial fitted to steering column, causing alarm imbobilliser faults.

    AUDI Q5 >2011  suffer AdBlue reset problems, dash indicates 1500 miles to go.  Fill Adblue tank take it for a short ride and dash never resets (time clock to non start).  No coms to exhaust trement module.  Some will update (software).  Some are go dead when they activate.  They are repairable (mostly).

    AUDI 1.8litre A3 Series (1996-98). Fitted with Bosch Motronic engine management ECUs (mounted inside front scuttle). These ECUs suffer water damage due to blocked scuttle drain hose. As part of winter service, check and clear these drains.  Symptoms: 1) Possible history of intermittent misfire or difficult starting.  2) Car starts and runs for about 30 seconds, then cuts out.  Diagnostic Checklist 1) Visually inspect ECU and front scuttle compartment (access front engine) for evidence of flooding. If yes the ECU will need attention.  PLEASE DO NOT REMOVE ECU COVER - THESE ECUs FEATURE HIGHLY SENSITIVE MICROELECTRONIC INTEGRATED CIRCUITS THAT WILL BE PERMANENTLY DAMAGED BY NORMAL ENVIRONMENTAL STATIC CHARGES.

    All VAG TDi  models to date suffer internal ECU heat dissipation problems, so if you have an intermittent problems getting worse as the vehicle gets up to temperature, with no faultcodes, try positioning the ECU connected to the loom, where it can get a flow of cool air to it (hairdryer with no heat, no joke, it works!).  If things improve, ECU will need testing to eliminate it from the diagnosis process.

    All VAG electronic power steering models.  Power steering can fail after a battery low voltage or battery change, with a bit of patience they will reset after deleting the faultcodes and cycling the ignition.

    Battery change on all vehicles with Bosch Motronic fuel injection system. May cause fluctuating, excessive idle speed - engine starts after changing the battery.  If the battery is disconnected or discharged the Motronic control units lose their programmed and stored basic adjustments.  When starting the engine after the battery was discharged or disconnected, switch on the ignition for approx 10 seconds and then switch it off again. This makes sure that the old adaptation settings are used.

    VAG  Auto gearbox control modules can fail due to jump starting from a slave battery, they have weak protection diodes on the main PCB inside the auto gearbox control module.

    VW's fitted with Teves Mk20 ABS system suffer faultcodes stored for ABS faults when ABS system operates correctly.  These ABS modules can be repaired and reprogrammed.

    All VAG TDi  pre-PD suffer problems with drastic power loss, causes: injection pump internal collapse or air flow meter fault.  EDC diesel pumps are known to fail from "cavitation" due to an ingress of excess water.  Water separates out from the fuel over time in diesel filters, and if the filter housing if not drained down at intervals.  The water will damage the pump beyond repair.  Most car manufacturers are now fitting new type water level sensors to filter housings on new models.  Supermarket fuel is jokingly called emulsion in the trade, due to its high water content.  Its cheap for a reason!   Some early VP44 pumps are known to fail due machining errors in the axle rota head, a few of these wreck the alloy pump body, rendering the pump unserviceable.

    VW TDi PD  Uneven running & power loss. Cause maybe pump unit failure, due to corrupted internal seal (not an expensive repair).

    VW TDi PD  High mileage vehicles.  Can suffer rough running like the "timing is out".  Due to worn cam running the combined PD injector pumps.  This is normally due to using standard 10-40w oil.  Use the correct 5-30w oil if you want your engine to last!  This problem is expensive to fix, long labour times and a substantial pile of parts is required!

    VW Mk5 Golf 2.0 TDi PD  Non start, caused by, live feed missing from ignition barrel to main EDC ecu.  Canbus errors highlighted by all other modules on car, ABS, instruments showing faults relating to main engine ecu.  If the fault has been intermittent, it can damage Canbus gateway and the main ecu.  Expensive..

    VW TDi PD.  Faultcode Cylinder 1 - 4 below/above control limit”.  Invariably will have a clogged fuel filter or fuel lines.

    VW TDi PD.  Suffer misfires, due to damaged wiring harness that run thru the rocker cover.  Beware it is possible to damage a new loom, when threading it thru the silly space provided.

    VAG 2.0 TSi engines fitted to passats and A4 A6, suffer premuture piston ring failures.  Plus noisey high pressure fuel pumps.

    VAG DSG gearboxes fail wholesale.  Mechatronic units fitted to wet clutch system installed on diesel models fail due to not having gearbox oil and filter changes every 40.000 miles.  (Petrol models are fitted with a dry clutch and do not suffer with early failure rates)

    VW Golf TDi early models.  Heavy rain can get in to the air filter.  As a result the air mass meter can get damp leading to brief running problems.  After the moisture evaporates the mass meter will work again.  Some models were fitted with Nordic spec air intakes by mistake.  Which have a mesh flap that collects debris and restricts airflow.

    VW Golf TDi with VE pump not PD.  Suffer cold start problems due to air leaks in the fuel system.  Visible as bubbles can be seen in the clear fuel pipes.  Engine is difficult to start and misfires.  Air is drawn into the fuel system through leaks in the fuel system, on pipes, pipe connections, fuel pre-warming valve or faulty fuel gauge sender unit.

    VW TDi with VE pump not PD.  Faultcode “17656 injection start control, control difference”.  Invariably will have a clogged fuel filter or fuel lines.  We have had to remove & clean lots of fuel tanks on these models.

    VAG 1.4TDi (3-cylinder).  Non-start after engine has intermittently cut-out.  No fault codes stored.  Cause maybe, internal arcing within the engine control relay.  This causes low control voltage to the radial control circuit.  Which includes the cam-crank sensor and the injector power supply.  Fault will exhibit itself as low voltage-current amplitude at the diesel  injector coils.  If the car is driven for long periods with this fault, it will normally damage the boost capacitor within the HDI modules of the EDC system.  Sometimes the HDI module is a cheap fix, sometimes a new one is needed...!  I really like this tiny engine.  I've seen some high mileage ones that still run like a dream.

    Skoda VRS diesels.  Suffer from blocked DPF filters, passive regen does not seem to work.  Forced regen does not seem to work either.  Very expensive repair, £1500 for parts.  Rumour of software updates from VAG on the way.

    Skoda Superb II 2010>  Suffer steering wheel rotary connector failure, loss of horn and control buttons on steering wheel.  Airbag, brake warning lights on!  Expensive part at £230 but easy to fit!  Be careful with part numbers, dealers will sell you superceded parts that will not work on your vehcile.

    Skoda Superb II 2010>  Suffer water in passenger footwell, aircon evaporator drain dies not allow water to escape.  Water drips from cabin filter housing!  Evaporator drain was installed incorrectly at factory.  Remove centre console side trim in drivers footwell and re-route drain pipe under electrical cabling instead of over it!  This will allow water to run out of drain instead of backing up...

    Later 2010> VAG engines 2.0 CR engines fitted to Superb II and Transporters.  Are known now to "right themselves off" when the Aux belt tensioner fails causing the Aux belt to shred and wrap around the bottom pulley.  The problem with the repair process is.  This type of engine has a pair of fragile cams which bend and the deflection cannot be seen "by eye".  If you do not change the cams, you may get loss of power and misfires when you start up the re-built engine.  Aligning the new cams in the fragile alloy cam carrier built into the head is not for the faint hearted either.  Get it wrong and the carrier will break when you start the engine up.  Then you will need a new cylinder head.  This is not a DIY job.  The pile of parts needed to do the job will cost about £1800 without labour (14/04/2014).  FIA now sell pattern cams, which will reduce the cost (30/11/2015).  We have repaired four Superb II and six Transporter engines that have failed in our workshop to date which have failed for this fault.  So the advice is:  if you need a Aux belt tensioner, go to the dealers and buy the correct one, which has a part number for the correct engine code (differing tensions).  Don't buy a generic pattern part!

    VW Beetle 1.8 & 2.0 Sparkplug replacement takes me two hours.  You will need a very long 6mm wooble drive allen key to remove the air intake and air purge pump off, to gain access to the sparkplugs.  Only use Iridium plugs and genuine HT leads.  It is such a nasty job, you do not want to be repeating it when poor quality pattern HT leads wobble off and cause a misfire.  Coilpack can be changed in 30mins thou.  What a stupid design, sparkplugs should be accessible, they are a service item.

    VW VR6's have a most useful plug lead removal tool clipped to the bonnet stay.  Beats bending up a cheap pair of long nose pliers to do the job.  Or worse...  Buying the special tool!

    VW newer diesel engines 1.2 - 1.4 - 1.9 - 2.0  UIS-EUI-PD systems  Although regarded as a whole new system the actual principle of this injection system began with the American engine builders, Cummins.  The Cummins PT systems was fitted to many trucks and became a legend at that time, due to it's reliability and economy.  UIS (unit Injection System), EUI (Electronic Unit Injection) or PDE (Pump Duse Einheit) systems are fitted to an increasing number of vehicles including Volvo FH12 trucks, LandRover TD5. This injection system also has no distributor injection pump and injection pressures up to 2000bar are achieved via the cam shaft acting upon the individual pump unit per cylinder.  Again, this system is highly sensitive to contamination and the price of replacement parts is very high.  Fitting PD injectors wrongly can wreck them, be warned!

    VW Golf / Jetta all models >2005 suffer erratic instrument cluster function faults.  Problem with host wiring.  Erratic instrument cluster functions, MIL on, Lambda fault codes present.  Bad earth connection under the battery tray in the engine compartment.  Battery will have to be removed to access the fixing studs.

    VW Sharan auto gearbox models suffer from control box failure due to voltage surge from jumpstarting from a slave battery.

    VW Sharan 2.8 V6 auto suffer cam-chain breakages at 80-90.000 miles.  Even if not broken, the chain replacement job takes, 16-18 hours of labour, and a minimum of £400 of parts.  As the chain is at the wrong end of the engine, which means the engine gearbox has to come out, then split on the floor!  Vile job to be avoided, I've done three & will never do another.

    VAG 1.8T Engines with AGU code.  Faultcodes for hall sensor, map sensor, & idle adaption.  Problem with loom damage.  Wiring chaffed through under battery tray, above gear change linkage, loss of 5V feed to the sensors.

    VAG Passat 2005> to replace the parking brake pads you will need specific electronic equipment to wind back the brake calipers.

    VW Crafter vans 2011 onwards.  Fitted with 2.0 TDi CR and Bi TDi CR engines suffer head gasket like symptoms due to EGR cooler failure.  We offer an engineered solution to this "in house" at our workshop.  Click on the link.

    VW Transporter T4 diesel models.  Suffer intermitant non start due to powerhold relay to the ECU which fails.  VW sell an unrated one with a better coil in it.  Frustrating fault will only show its ugly head when diagnostic equipment is plugged in, loading ECU up causing coil to overheat and fail.

    Golf Jetta Passat DIGIFANT II ECU's 1988-1990  Non start following work on clutch, gearbox or starter motor - fault causes continuous injector operation with extensive petrol flooding of cylinders - or, rarely, no injector pulses.  This problem is caused by failure to properly replace clutch housing earth strap. WHEN STARTER MOTOR IS OPERATED, MOTOR CURRENT RETURNS THROUGH ECU CAUSING IMMEDIATE AND EXTENSIVE ELECTRICAL DAMAGE TO ECU.  Digifant ECUs can be repaired and rebuilt by us.

    VW T5 2.5 PD engines suffer broken valve followers, plus they wear the cylinder head injector ports, needing the purchase of a new head.  Evil gear driven cams need loads of special tooling to re-time.  Not a job for the faint hearted!

    VW T5 2005> 2.5 130 and 170 BHP models.  Suffer premuture DMF and clutch failure.  Due to wear on gearbox input spline.  Slight wear causes rotational side loading on dual mass flywheels everytime you depress the clutch pedal!  Very expensive fix!

    Worn T5 gearbox input shaft.


    Later Audi TDi gearbox with built in clutch and flywheel.  Fitted with Sach type carrier clutch and flywheel.

    Replacement is very expensive and time consuming!  Not may garages will take the job on!  We will thou...


    VAG Diagnostics.  VAG has not suffered the same software problems and glitches with electronic control units that GM, BMW and countless other manufacturers are prone too.  Thus avoiding the constant need to “upgrade software” or buy later modules to overcome these faults.  Electronically VAG is definitely a better product than the current industry standard.  Onboard diagnostics, including real time live data is excellent and manufacturer specific faultcodes are readily available to the trade. The ease of which it is possible to reprogram modules & code parts up, puts all other manufacturers to shame.  Information systems including ElsaWin & Ektra cover everything imaginable.  Independent diagnostic systems are available which offer dealer spec diagnostics and reprogramming at very low cost.  Rosstech VAG-COM is excellent.  Go into any main dealer VW-Audi main franchised workshop.  The technicians have laptops loaded with VAG-COM.  Reason being, on connection VAG-COM gives an instant display of all modules and systems.  Its easier to use & the software support is better than VAG software.  For £200 you can buy the latest licensed version of VAG-COM, multiplexer and lead, this includes all updates for the future.  £40 will buy you both recent edition copies of Elsiwin & Ektra from eBay (15-11-07).  So if you are in the motor repair trade and considering specializing, look no further than VAG.  Taking into account the need for service light reset, electronic parking brake reset & diagnostics, buying a genuine copy or VAG-COM with all the functions working and free future updates, is superb value for money.

    VAG engine re-mapping.  VAG group cars do respond to re-mapping well.  Only a fool would attempt it on a BMW or Mercedes!

    Page updated 21-02-18

    (date information written)