Avdwaal1

hi,

2006 audi A8 base. I had these codes and many more and cat and evap not ready.

[Explanation of codes ADDED]
P0150=02 Sensor Circuit Malfunction (Bank 2 Sensor 1)
P0155=02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
P2254=02 sensor negative current control circuit/open bank 2 sensor 1


I replaced the o2 sensor (driver side) and now i still have the codes listed in the subject. It seems the o2 sensor heater is not working as it should. i i also checked the vacuum lines, they seem ok. I read somewhere the o2 sensors are controlled by the fuel pump relay?

I checked the relay, the number on it is 191 906 383C. I went online to look for a new relay and several sites suggest the relay should be 8E0951253? Does my car have the wrong relay? Any other thoughts/suggestions?

Tnx.

MP4.2+6.0

As a BTW, no one I know of has these codes memorized, so you will get better answers if you go on to post what they mean. Or, use the VAG COM output which has a text description.

Meanwhile, since you say sensor heater is not working as it should, I would check the physical connector where you plugged the 02 sensor in to the wiring harness before pursuing these other ideas. If you used OE or Bosch (or maybe others), it should have been a direct plug in. If so, look at the car side plug--where the connector locking tab that is easy to break is. Obviously look for broken wires, but also for any (female) connecting pins that have pulled back into the connector housing; you have to open it to see that probably. BTDT. It should be a six pin connector, with 5 of the 6 pins occupied. If you used some other brand of O2 sensor you had to splice in, besides being suspicious in general, review all the connections.

Avdwaal1

I added the description of the codes, good point.

The sensor is a Bosch and it was a direct plugin.

I'll check for the (female) connecting pins.

What about the relay? What type is yours?

MP4.2+6.0

Never touched it--on any of my modern Audis. Seems like a pretty esoteric fix idea to me, hence the more basic stuff like the connector that is prone to damage and issues. But, if you want to troubleshoot it, I would just voltage meter it at the connector first.

Here is a post on the wiring color codes: http://forums.fourtitude.com/showthr...ng-color-codes Notice one of your codes is on the negative power lead for the heater element; thus, look even more carefully at the white wire situation at the connector. If you find voltage at cold start up on the heater element leads, then it has to be localized at the connector or a still defective O2 sensor. If not, then yes it is upstream at a relay, other control electronics or wiring leading to that connector.

Avdwaal1

I started the engine, it was a "cold" (it is 62F here in CA) start.

The voltage over red and white is about -1.50V.
The voltage over Red and ground is about 3V.
The voltage over White and ground is about 5V.

The voltages are the same on both connectors. Kinda weird since the bank 1 sensor does not give any codes.

Arthur

MP4.2+6.0

You are seeing voltage, an indicator obviously that the circuit is complete. However, on the 02 reading wires for the sensor, I think the voltage will vary. On the heater circuit, I think it is pulse width modulated and designed to heat in the opening seconds; thus I think not practical to test with a VM beyond just basic current/no current right at cold turn on that you have confirmed. BTW, "cold" for these relates more to exhaust gas and O2 sensor temps, rather than any ambient temp. weather issues for milder Bay Area or summer weather.

As another idea since you mention both (forward) sensors, assuming the O2 connectors are near each other, try swapping the two connections temporarily. (I have a W12 so have lots of these, but each motor lays out differently for where the connectors are.) If the supposed issues/codes "move" from bank 2 to bank 1, that suggests to me it is either (still) a sensor issue or a fuel/air/emissions equipment issue on the true bank 2 (U.S. drivers) side. If they stay with bank 2 even with the connection swap, then it would be somewhere in the electrical/electronic circuit on the bank 2 side. Given your O2 related signal codes, I expect there is an issue somewhere in that system just as you do.

Also, on your voltage testing, verify the female pins on the car side of the connector are all the way out toward the inner face where they mate up to the male pins on the sensor side of the connector. The pins can creep up inside the connector when they are plugged together if the pin got damaged--can happen if the connector housing is ever changed. Been there, seen that on mine.

Avdwaal1

I verified the connectors on the car side, they are fine, no pins creeped up.

I just cleared the codes, swapped the connectors and drove around for a bit. Now I got:
P2196 O2 Sensor Signal Biased/Stuck Rich (Bank 2 Sensor 1)
P2197 O2 Sensor Signal Biased/Stuck Lean (Bank 2 Sensor 1)

MP4.2+6.0

So, if I am still following, even with a sensor connector swap, it continues to show on "bank 2," which temporarily is now the actual U.S. passenger side with the swap instead of the driver's side. That leaves the electrical and electronic from the connector on back it seems. But also notice no code for the signal type issues, which were all the prior codes you flagged. That may be a connector seating or oxidation issue now addressed. But you may also need two driving cycles (motor temp cold to hot to cold--needs like a 6 hour gap) to force one of the lesser code type issues out. The O2 codes seem to show right away in my experience but some like the air pump, EGR, etc. are usually the two cycle type.

Given from the current codes so far it sees all the way rich to all the way lean though (albeit only one sensor on what is now the true driver's side), I would also look for vacuum issues again. Probably need to dig into diagnostics in Bentley/alldata/other technical resource at this point to try to unravel.

Avdwaal1

I bought vagcom from rosstech. I'll post details of the scan once I have received the cable.

Avdwaal1

I have finally replaced both O2 sensors, but still get:
P0150=02 Sensor Circuit Malfunction (Bank 2 Sensor 1)
P0155=02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)

I have checked the vacuumlines as best as I could (found one loose connection), cleaned the MAF sensor. What else can I try/do?