BMW 523i E39 1996 - Fault code 203 bank 2 O2 sensor and lumpy idle #
Posted by Ian Staples on March 1, 2009, 7:12 pm
Year of Manufacture *: 1996 Engine Code or Type *: 256S3
Hi all.
BMW 523i, 1996, E39, 256S3. Fault code present is 203-O2 sensor bank 2 performance cyl 4,5,6. Live data shows both sensors are open loop until temp reaches 80C, then both go closed loop but only bank 1 switches, bank 2 stays at 4.6v, at this point engine runs smooth, after a few minutes bank 2 goes open loop and bank 1 remains closed loop and engine runs a bit lumpy. Fitted new sensor, still the same, swapped sensors over, still bank 2 faulty. Did notice that when i swapped the sensors over, the new one that was fitted in bank 2 was like new, i mean really clean like it had never been fitted, those three cylinders are certainly not doing anything.
Gas readings when fault present - O2 5-6%, HC 800, lambda 1.2-1.3, gas readings for the few minutes that both sensors are closed loop even though only 1 is switching are within limits (i wouldnt expect them to come right down low instantly as it just come off a fault).
Cant pin down a misfire when fault present, and the plugs all look the same. Have removed inlet manifold, inspected and replaced gasket and hoses, still the same. Fuel pressure is good. Inlet vac reading is good. Compressions are good.
My next plan is to swap injectors around to see if the fault shifts banks, but i cant see 3 injectors suddenly giving problems. The wiring shows the injectors having a common connection and then six connections to the ECU.
Ive probably done a few other tests and failed to mention them in this post.
Re: BMW 523i, E39 - Code 203 bank 2 O2 sensor and lumpy idle
Lambda sensor dtcs on these are usually caused by air leaks.If the inlet manifold has been off ,then I would assume that the breather pipe between cyls #1 and #6 is ok.Another common fault is the crankcase breather/oil seperator valve (sits under inlet manifold).Looks like ice-cream cone.Also is the oil filler cap a tight fit?
Re: BMW 523i, E39 - Code 203 bank 2 O2 sensor and lumpy idle
All the air and breather pipes have been inspected and found to be ok and manifold refitted.
Blanked off where the breathers enter the manifold and made no difference. I know what you mean, ive had the breather unit give grief before.
Oil filler cap is a tight fit too.
CAT has since given up and was undrivable, so opened up and removed contents and welded back together, drives fine again but still has this fault, which is clearly whats seen the CAT off. Will replace the CAT when (or if, ) this fault is fixed, no point at the moment.
Re: BMW 523i E39 1996 - Fault code 203 bank 2 O2 sensor and lumpy idle #
"BMW 523i, 1996, E39, 256S3. Fault code present is 203-O2 sensor bank 2 performance cyl 4,5,6. Live data shows both sensors are open loop until temp reaches 80C, then both go closed loop but only bank 1 switches, bank 2 stays at 4.6v, at this point engine runs smooth, after a few minutes bank 2 goes open loop and bank 1 remains closed loop and engine runs a bit lumpy."
What is the voltage on Bank 2 sensor after it goes Open loop and the engine starts running lumpy???
This is important as has been pointed out by others re air leaks.
"Gas readings when fault present - O2 5-6%, HC 800, lambda 1.2-1.3, "
Readings indicate a lean misfire. Was the HC reading drifting up and down?
"gas readings for the few minutes that both sensors are closed loop even though only 1 is switching are within limits (i wouldnt expect them to come right down low instantly as it just come off a fault). "
0.45 to 0.495V are with the ECM's programmed Stoichiometry range BUT the ECM would expect to see some switching after engine reaches NOT.
Any codes stored???
Cheers
PeterW
Re: BMW 523i E39 1996 - Fault code 203 bank 2 O2 sensor and lumpy idle #
Bank 2 O2 sensor when fault present and open loop and lumpy, im sure it stayed at 4.6v, but i'll check my notes again. You mentioned "0.45v to 0.495v", i think you are refering to the wrong type of sensor there, 0-5v is the range of these, not 0-1v.
I agree, gas readings do indicate a lean mixture causing a misfire, and its only on those 3 rear cylinders, and it cant be narrowed down to 1 cylinder. Again i will check my notes on the amount of drift.
As the engine reaches operating temp, both sensors go closed loop, but only bank 1 sensor switches, it takes a few minutes for the ECU to register the fault and indicate an open loop state on bank 2.
"Any codes stored???" A clue is in this posting title, code 203 - O2 sensor cyl 4,5,6 range/performance.
Re: BMW 523i E39 1996 - Fault code 203 bank 2 O2 sensor and lumpy idle #
on March 2, 2009, 12:14 pm, in reply to "
) this fault is fixed, no point at the moment.