The Cost of Free Diagnosis

The Cost of Free Diagnosis

Let's start with some basic examples of the process of diagnosing a vehicle.


Let's say there is a customer with a 2004 VW GTI with a 1.8t engine in it.  His check engine light comes on and he brings it to the dealer.  The dealer scans the fault codes and finds this fault.

16795 / P0411 - Secondary Air Injection System: Incorrect Flow Detected


The technician now has a direction to start his diagnosis.


The secondary air system is installed on the vehicle for emissions purposes.  It injects air into the exhaust to assist in burning unburned fuel in the exhaust system before it reaches the catalytic converter.


The secondary air system consists of some simple parts.

  • The Combination Valve also called Kombi Valve(this valve opens and closes to control when the air flows into the exhaust)
  • The Secondary Air Injection Pump (electrical pump that pumps air)
  • The Secondary Air Change over valve also called N112 valve (this valve controls the opening and closing of the Combination valve)
  • The Secondary Air Pump Relay also called J299(this controls the power to the Secondary Air pump)
  • The Pipes that carry the air to and from the secondary air pump



The technician will likely start by checking the hoses for the secondary air pump to be sure that they don’t have any cracks or breaks in them.  Then he will run a protocol on the vehicles diagnostic to electronically operate each part of the system.  Once he has ruled out the Air Pump, Change over valve, and Relay.  He will take a vacuum pump to check the operation of the Combination valve.

Let's say it all checks out good, then what?

If you brought your car to the dealer or a shop who specializes in VW and Audi they know that this fault is sometimes caused by a bad Diverter Valve also called DV, or Turbo Recirculation Valve so they will take their vacuum pump and check to see if the diverter valve holds vacuum.  If it doesn’t then they know this is your issue and your vehicle has been diagnosed.   Customer needs a new Diverter Valve 06A-145-710-N



Now let's say the same customer takes his vehicle to an Auto Parts Store. 

They scan his vehicle and print out his fault codes.  So now he knows his fault is P0411- Secondary Air Incorrect Flow

What does he do?

Possibly with some help from the gentleman at the auto parts store they can look at the secondary air hoses to make sure they are not broken or disconnected.  Once they have verified this is these are good what do they do next. The scan tools they have do not have any test features so they don’t have any more ability to diagnose any further.

What happens next might vary but most people would probably start replacing parts.  Maybe you start with the least expensive the Secondary Air Pump Relay, and then move on to the Changeover Valve.  Once you have replaced them maybe you go buy a Combination Valve, and once that doesn’t work finally the Secondary Air Pump.


Replacing all of these parts with aftermarket parts is over$650.00 just for the parts.



So all this time and work and money have been spent either working on the vehicle or paying someone to do so, and your problem I still not fixed.  By this point I’m sure our customer is a pretty frustrated guy, and may take his vehicle to someone to diagnose the vehicle.  If he does so, he will find out that for the vehicle could have been repaired for around $250.00and save a lot of time and aggravation.


I offer this insight to anyone interested to possible help guide you to the understanding, that when you pay for vehicle to be diagnosed the technician doesn’t just plug in the car and know what the problem with the vehicle.  It always requires further investigation.

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