tatatana

Hello,
I have a working 2001 Audi A4 quattro AWD 1.8 with the engine light on and with a mileage of 115kmiles.
I scanned the car twice, first time :
P1114 Bank 1 Sensor 2, Resistant Too High
p1118 Oxygen Sensor Heater Circuit, Open Bank 1 Sensor 2
p0140 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
p0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2 Sensor 2)
Warm Up Catalyst Efficiency Below Threshold (Bank 2)

Read more at: http://www.obd-codes.com/p0431
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p0134 02 Sensor Circuit No Activity Detected (Bank I Sensor 1)

Then I reset the car and drive it for one day :
p1114 Bank 1 Sensor 2, Resistant Too High
p1118 Oxygen Sensor Heater Circuit, Open Bank 1 Sensor 2
p1400 EGR Valve Circ Electrical Malfunction

I would like to know what should I do?replace all O2 sensors, only the downstream ones or?
And what could happen if I do nothing?
What is the most important the O2 sensors or the EGR problem?

Prospeeder

Yes replace the rear oxygen sensor. As for the P1400 which is actually secondary air injection related im sure, since these dont have EGR. Just visually inspect the vacuum hose from the air injection valve on the rear of the head, to the solenoid under the manifold. Then the supply vacuum from the solenoid to the intake. Then that the plumbing from the pump to the valve are intact, and that the pump operates for 2 minutes when the engine is started cold. The pump is in the lower passenger bumper area. Theres also the relay for it in the box under the wipers with the ECU, as well as its 40 amp fuse.