Audi A3 1.6 8V petrol high emissions


Hi, i have high emissions on my A3 1.6 petrol. The lambda is about right but the CO % is too high. I have no fault codes stored in any system. The rear O2 sensor is at a steady 0.7V, which I would expect, but the front O2 sensor is at a steady 2V although this is a wideband sensor. Any ideas? O2 sensor or CAT possibly?

Where are you measuring that? Wideband sensors deliver information over CAN, not through voltage. You read it via a scan tool in Lambda… which should be a steady 1.0.

High CO is a sign of poor combustion. Since there is no check engine light… I doubt the CAT or O2 sensor is at fault, especially if you can scan the data and see Lambda right at 1.0. I’d be thinking it is not fully up to temperature, the wrong spark plugs are in the engine or maybe the compression is low.

How many miles on this engine?

High CO implies the possibility of an overly rich mixture, preventing complete combustion

This is what is suppsed to happen

CH2 + O2 = CO2 + H20

This is what is happening on your car

CH2 + O2 = CO2 + CO + H20

So either too much gasoline, or too little air. Checking fuel pressure and replacing engine air filter seems like a good idea. Correct equation requires a lot of heat too, so double check coolant is correct operating temp. If not, replace thermostat or whatever is causing coolant temp to be too low.

I’ve had a too much HC problem on my Corolla before, not the same as too much CO, but this might be helpful for ideas anyway. Is your emissions testing done parked at idle, or on a car treadmill at speed? Suggest to not assume it is cat, could well be something easier to fix. Tell us how your 1.6L A3 engine is configured? Model year? Distributor or coil on plug?

Ive fixed the problem, turned out to be corrosion on the coilpack! When I pulled the HT lead off, the leg on the coil pack was that corroded it snapped off! New plugs, leads and coil and it passed no problem!


Great, thanks for letting us know.