All oxygen sensors CEL at once Audi a4 Avant 3.2 2008


Two days prior everything except EVAP (cel for 2 years now) worked. This morning car was totally bucking and these appeared on the OBD:
1.P2401 Evap Emission Leak; Detection Pump Control; Circuit Low
2.P0031 HO2S Heater Control Circuit; Low Bank 1 Sensor 1
3.P0051 HO2S Heater Control Circuit; Low Bank 2 Sensor 1
4.P0037 HO2S Heater Control Circuit; Low Bank 1 Sensor 2
5.P0057 HO2S Heater Control Circuit; Low Bank 2 Sensor 2
6.P2295 Fuel Pressure Regulator 2; Control Circuit Low
7.P2009 Intake Manifold Runner; Control Circuit Low Bank 1a
I cleared the codes, disconnected the battery for overnight. Reconnected, started engine; rough; checked codes all back.
suggestions from variety of Web comments to check fuse for heater/oxygen sensors. If there’s a fuse on this car I cannot find it. So what to do?

I’d find the pin out of the plug to the O2 sensors to determine which pin is the hot pin for the sensor heater. Then start the engine and check for voltage on the plug side, you don’t need it plugged in. If there is no voltage, then it isn’t coming from the PCM. Then you go looking for that mysterious fuse.

The P2401 may not mean there is a leak. The fault is detected in the Evap emission leak circuit. The fault appears to be that the air pump motor isn’t working or air isn’t flowing. It could be that its air filter is clogged up. If you went through some pretty deep water, that could be the cause.

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Thanks. I’ll give the voltage bit a try. Hopefully I can locate the pin.

My concern with this problem is why two mornings after the car ran fine did the codes for all sensors (I assume there’s four; 1 near exhaust headers and 1 near the catalytic converters) all come on at exactly the same time? The battery voltage was 12.33.

It is likely that all four oxygen sensor share the same power source for the heaters, if the power source fails none of the oxygen sensor heaters will operate.

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I would strongly suggest one of the many Audi enthusiast websites out in the ether… They will have seen and know how to direct you with this issue. It may be a fuse or a relay…and we both know how much Ze Germans love fuses and fancy relays… At least I do anyway.

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Probably a problem w/ one of the main power supply voltages. There’s definitely a fuse for the o2 sensor heater control circuitry, and it makes sense to check that first. The question is: which one is it? There’s lots of fuses and in many locations. I’d guess that one is in the engine compartment, but just a guess. Suggest to start by looking in the fuse section of the owner’s manual. A shop that services Audi and has access to the wiring diagram will be able to find that fuse for you.

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Original ECM being replaced by a used one but both have the exact same Audi part number and manufacturer’s number. My Audi is a 2008 A4 3.2L Quattro Avant with Tiptonic auto transmission.

Original has had a P2404 (EVAP problem) for some 4 years that the dealer has declared the ECM is at fault and needs replacing. All tests including wiring and vacuum lines are ok.

They want $2,439 + $80 to set it!

In addition they said the vacuum was 19.1 inches at the leak detection pump and should be above 20 so they want to replaced the booster vacuum pump for $858!. I bought a new one from a supplier in Phoenix, AZ for $48.56 + a gasket locally and replaced it myself. Not easy but worked out fine with vacuum now at 20.5

I bought the used one from a parts salvage yard in Lithwania, which was delivered via DHL in three days two hours! (pretty amazing!) I replaced the original with the used one without disconnecting the battery (bad me but…) then turned on the ignition without starting. SAFE appeared where normally the total mileage would. The trip odometer remained at 157.X. OBD II meter had 6 codes: 4 for the cam, 1 for fuel pump, and the dreaded P2404! The VIN number was different but checking on it showed the ECM came from a 2008 Audi sedan with a 3.2L engine.

Question: should I clear the codes and start the engine? Anyone’s suggestion here would be greatly appreciated.

I’ve posted here before about fuses I could not find for the ECM but after removing the improperly secured case for it, discovered the fuses and the TOTALLY corroded and rusted relay switches that causes some 9 code errors just a few months ago. Both replaced and I’ll put that episode in this forum sometime latter with photos.

You’ve now got 2 threads, and your last post appeared in the other one, which I responded to

In other words, you should consolidate your 2 threads into 1

I know. I tried to remove these latest comments from the old thread after thinking that not many responses would be forthcoming but could not figure out how to do that.