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O2 sensor

Having O2 sensor bank 1 heater circuit short on a 03 BMW 325i. Changed O2 sensor, reprogram DME - no solution!
Symptoms: chk eng light - code p2231
Engine surge upgrade
Poor gas milage

Come on guys, no bites at this apple?

Have Check Engine Codes on O2 Sensor and Speed Sensor for 1996 Lexus ES300, with high miles. When codes were reset previously, the vehicle passed the smog test, but the radiator blew within 35 miles! Two years later and with a new radiator in toe, it needs another smog check now and am told I need a new or rebuilt transmission when they recently “pulled codes.” However, the car has a checkered history: it was stolen and recovered; it survived another hit-and-run at the gas pumps affecting the front end and it was rear-ended while stopped for a jaywalker, too. As the shifting problem it now experiences occurred shortly after a more recent hit-and-run accident (affecting the driver’s door), could the thrust of force on the door have disrupted anything internal to the tranny? Or, is it more likely that the poor ole’ Lexus is just “mechanically-exhausted” and should finally be retired to the closest “James Bond Museum” for classic-car crashes?!?!?"?!?!?

@jsprar, the code refers to a shorted circuit on the O2 sensor heater. If a new sensor did not fix it, then the circuit needs to be looked at. The short is not always in the sensor.

The only thing I will add is that based on the surging and poor fuel economy there may be issues other than an O2 heater sensor circuit and I’m assuming the correct upstream O2 was changed and not the downstream one.

Thanks for adding to the conversation. Agree there is something else wrong but the question is what??? Dealer claims they bypassed harness and wired sensor directly to DME as part of their testing. This claim rules out wiring harness ??? Wish they had kept the bypass on for an extended period - at least I could have confirmed they actually did it. Think they want to sell a new DME ( DME is programmed vin specific - can’t buy used)

You won’t get a lot of help here for a specific issue like that on a BMW. German cars are notoriously overly complicated (Rube Goldberg affairs) and they keep repair information close to home. You are at the mercy of the dealership.

I have not worked on that many German cars…a few Passats and only one BMW.
But I have to give them some credit. I currently am replacing the Water Pump on a BMW 525i and found it very mechanic friendly.
Unlike any American car…where you have to remove almost everything that runs off the belts and their brackets, this one is simple.
Pull the fan shroud and fan, a few hoses, remove the serpentine belt, remove the pump pully, remove the 4 nuts holding the pump in, and pull the pump. They even give you two threaded holes that when you run two bolts into them, they push the pump and it’s o-ring from the housing.

An American company would design it so you’d have to buy a special puller…another tool.

It took me less then an hour and the new pump is in. I just have to wait now for the thermostat and housing that was the real leak problem. There was a small, dried spray of coolent under the hood and even a pressure test showed no leak. A friend of the owner convinced him it was the pump and he insisted I change it out. I ended up finding that the temp sending unit on the thermostat housing was rotted out inside.
THe prices though…pump $50 Thermostet housing with thermostat $110 holy housings.


Well, thanks to all who contributed to the discussion. The dealer promised a plan of action by 7/30/14.

I have never seen a water pump that requires a puller of any kind. But a new one for $50? Hate to tell you want a new one cost for my Saturn, but the Thermostat and housing was a lot cheaper. No fan to remove on the Saturn but it did have six bolts instead of four.

Caddy made a water pump that twist locked into postition. Of course if you had to remove it, it was stuck and just would not come out.


I believe you needed a special tool to remove that pump

Are you saying it wouldn’t come out, even if you were using the correct tool?

@Kieth; You read too fast and don’t think about what a person is saying.

From my post
"An American company would design it so you’d have to buy a special puller…another tool."

I’ve never seen one either, but “If an american company designed this…they would make it so you had to buy a puller”

THe prices though…pump $50 Thermostet housing with thermostat $110 holy housings.
Sorry, I should added the word Cheap behind $50

$110 Holy housings…doesn’t that sound like, I think it’s high.

Comprehension is everything!!!


Ok guys, here is the update. Decided against replacing the DME - main computer. Instead, bought an OBDII scanner and learned a lot about fuel trim. Ended replacing the downstream O2 sensor for bank 1 - bank 1 sensor 2 based on the fuel trim numbers. So far, original - code P2231 - has not returned.
Moral of this expensive hunt? Replace O2 sensors in sets, analyze fuel trim #, and other live data before contemplating repairs. A fault code on an individual part doesn’t mean that component is defective.


P2231 seems to be for the heater circuit of Bank 1 sensor 1 . . . the upstream sensor

You said you replaced the downstream sensor . . . that would be bank 1 sensor 2

Is it possible you actually replaced the upstream sensor . . . the one before the catalyst?

Because the downstream sensor’s only purpose is to monitor the catalyst efficiency. It shouldn’t have an effect on engine surging

Forgive me for saying this, but something doesn’t quite add up, in my opinion

Yes, bank 1 sensor 2 is the one AFTER the cat. Replaced bank 1 sensor 1 - before cat - twice. It appears computer uses BOTH sensor output to calculate injector pulse rate. Guess the delta between the two sensors did not compute!

On the side notes of special tools and difficult water pumps how about the GM Quad 4 where the pump is driven by the timing chain. Most of the manufactures today require special tools to work on the cars from pullers to tools to set cams. The days of a few 9/16 bolts and the water pump is off are long gone.



First you said “Ended replacing the downstream O2 sensor for bank 1 - bank 1 sensor 2”

Then you said “Replaced bank 1 sensor 1 - before cat - twice”

Which is it?


Like I said earlier, the downstream sensor is used ONLY to calculate catalyst efficiency

Friend, seems you are in the mood for fighting. My goal is not to justify the repairs that WORKED for my P2231 code. Instead, I am posting to give others options while trying to solve their O2 sensor problems.

Please don’t get upset with db4590. He knows what he’s talking about and the posts did come across as a bit muddled. He’s just trying to bring some clarity to the discussion.

You also had a complaint of poor fuel mileage. Problems that lead to fuel mileage can ruin O2 sensors so hopefully any sensor replacement is not a band-aid for the symptom instead of the cause.