Please Help!! I have a 2002 Audi A6 and it was working perfectly fine until a week ago! At the time, I noticed a small problem with the oxygen sensor and have decided to replace it. So I brought one off the internet. But after I change the sensor, my audi won't even start! Well, it would start the first time and then die, and if I try to start the second time, it won't even start up, just cranking. I thought it was a problem with the fuel injector, so I brought one and changed it, it didn't help at all. Everything else with the car works just fine, except it won't start.

I live two hours away from an audi repairshop/dealership, so there's no way I would be able to get the car there for them to check it out. Please Help!! I love this car to pieces!! Any information is welcomed!

 

The O2 sensor should not prevent the car from starting.
You must be having something else going on (bad fuel pressure regulator, bad fuel pump, bad air meter sensor, bad coolant temp sensor, bad ignition control module, bad coil/s, vacuum leak - if you unplugged stuff to have enough working room, did you connect everything back together after replacing the O2 sensor?, etc)
Did you have or do you have a CEL?
If you do, then probably the best first thing to do is to scan the car and retreive the DTC code/s, which most likely will point you in the right direction.

 

As Chefro said, you disconnected something while working on your car, probably the MAF sensor. Go reseat all electrical connectors and vacuum lines. Its something simple.

Good luck,

Bob

 

Thank you guys so much! I checked all the parts and I am almost certain that all parts are connected properly. Yesterday I tried to start the car, for the first time, it lasted more than a minute then it died again. Does that mean something, or if its repairing itself? Sorry this must sounds like a stupid question. Thanks for your help!

@chefro: can you buy the CEL online or do you have to go to a audi repairshop?

Thanks

 

CEL = "Check Engine" Lamp
also known as
MIL = Mulfunction Indicator Lamp.
It is the lamp on your dashboard that illuminates an yellow plastic "cover" that has a little engine painted on it. Any and every car nowadays has it and signals a malfunction.
If the light was on recently, or it is on - you need to scan the car to see what trouble codes are stored in the ECU (electronic control unit) memory.

If you don't know what CEL is, then how did you know the O2 sensor needs to be replaced?

 

I once ordered an O2 sensor from the web and it was bad. It could be that you have a bad sensor.

 

@chefro

Sorry about that, this is pretty embarrassing but I am really challenged when it comes to fixing cars. A friend of mine is an electrician and he knows a bit about cars, so he changed the O2 for me :-) No, the light was not on before he changed the sensor.

@hxgaser

My friend then changed back the old sensor, but we still have the same problem.

Thank you guys so much!

 

Ok, did you disconnect the battey when the sensor was being changed?

 

did not disconnect the battery when i replaced the o2 sensor, but the ignition switch was turned off when changing it.
now it still has the same problem: the engine only can start one time. the second time it won't start no mater it is in warm condition after running a while shutting down itself or after first start shutting the engine with the engine still cold. There's only P0050 when scan the ECU. after waiting about 2 hours, it can start just like normal again. but only one time starting.

now it using the old O2 sensor, scan is p0050. it does nothing with starting.

I try it many times. some times the speedometer is up and down very unstable . it evey lock the door after 30 km/h, luckly i have the other key in hand.

 

oh, by the way, already replaced the fuel filter, 6 sparkles,
checked the fuel relay when start the engine. first start the relay has output. but the second time, the relay coil lost power just on then off. when turn the key back from ignition, the fuel relay on/off one more times. it seems the ECU won't keep the fuel relay working.