Volkswagen Aftermarket Radio Caused Smog Test Failure

I have a stereo installed in my Volkswagen VW Cabrio which is not from the factory. It is an aftermarket radio.

From what the smog check place told me is my VW is failed the smog test because my MIL light wasn't working properly and that they could not get any data from my vehicle for the emissions part of the test.

Of coarse my Volkswagen fails the smog check now because the malfunction indicator lamp is not working. I understand that however how is it that the smog report has numbers for the emissions part of the smog inspection, indicating that my VW is a gross polluter if they can't get any data from the vehicle.

I would think that there wouldn't be any numbers on that emission part of the vehicle inspection report. Am I not correct?

Also the first thing that this smog station guy who did this smog test said to me was that the stereo in my car wasn't hooked up properly and that it would the MIL lamp to turn on as soon as a replaced the MIL lamp. He asked me who put it in my car because it wasn't the original stereo and it would cause a smog check failure. He specified first to get the stereo hooked up right and then get the MIL light fixed. He mentioned I will need to take my VW to a shop so they can find out why it is a gross polluter and then why the MIL light is illuminating. He also said it was going to cost me like $600.00 to do this. But he really insisted the stereo was the big problem. It doesn't make any sense to me. Will you shed some light?

Thank you very much.

Answer:

The smog technician is correct about your VW's stereo possibly causing the malfunction indicator lamp to illuminate. It will be known for certain after you replace the MIL light and get the light working.

In 1997 VW and Audi started installing radios (stereos) capable of self diagnostics in most of their vehicle models. In essence these were smart radios capable of sending fault information to the vehicle's ECU (engine control computer) as well as important speaker volume data, radio preset information, and various other media and control function.

In the early days a "k-line" connection was used to connected the radio to the ECU, and more recent computer systems use the CAN (Controller Area Network) system via the CAN-high and CAN-low signal wires.

In either case an improperly installed aftermarket stereo will severe ECU communication and trigger the Malfunction Indicator Lamp on; causing the vehicle to fail the smog test.

We recommend resorting to the original factory stereo, or finding a local professional aftermarket stereo installer who can wire your VW's radio to function properly with the ECU. It can often be done by installing an interface adapter between the aftermarket stereo and ECU. Search or ask about "Smart Radio Wiring Harness" for newer Volkswagen models.

posted by SmogTips Support