igzy

iTrader: (18)

After many months and parts replaced, I had finally solved my P0140 problem, yey

Here are the troubleshooting steps that I learnt along the way that may help you in the future should you get this code and if it does not go away after sensor replacement...

P0140 – Heated Oxygen Sensor malfunction Sensor 2 Bank 1 - oxygen sensor reporting lean condition to computer. In this scenario ECM (ECU) tries to add fuel (up to programmed limit) but it never sees Bank 1 oxygen sensor swing rich. So it sets code and defaults to table value for fuel delivery.

I tried to put it in order of price and ease of verification, so here is a check list:

1. Verify the sensor plug to the main harness – it can get loose; check the internals of the connectors themselves

2. Check for exhaust leaks near the sensor itself – repair if you find any

3. Change the O2 sensor – as sensor bank 1 is biased lean so it never signals to ECM that it is rich

4. Not necessary, but does not hurt to reprogram the ECM (ECU) if it has not been done and if you car falls into the TSB category (IMHO, I would avoid this unless you can get it done on the side)

5. Verify the wiring continuity between the O2 connector and ECM – ECM terminal # 72 and White wire from the harness (this is PITA as you will need to go behind the dash to check, so may want to leave it till later)

6. Unscrew and clean the ground terminals of the main harness that runs along the top front of the engine (two GND screws are located to the left of oil cap when standing in front of the car)

7. Check for vacuum leaks – you could use stathoscope to find a leak, main places to check are around PCV, intake, brake buster; also verify that all hoses are hooked up properly and not leaking at the plugs

8. If you have an oil catch canister installed, make sure it is not leaking anywhere like fittings, canister seals (at the end, this is where I found my problem! )

9. If you can, monitor the injectors operation and make sure they are working properly

10. Check the fuel pressure and fuel pressure regulator (FPR) operation – I know this may sound funny, but pull the vacuum hose off FPR and try sucking on it, you should not be able to draw any air out it, if you do, then the internal FPR diaphragm is damaged and FPR needs to be replaced. If the overall pressure is down while the car is running, your fuel pump may be on its last legs

11. You may want to think about changing your fuel filter as insufficient fuel supply may cause it too

12. Pour some real good injector cleaner in (e.g. BG44K) and drive it for some time to get it through the system or get them cleaned professionally

13. Verify that coils harness is plugged in properly

14. Change the spark plugs – one of them may be faulty and not burning all the fuel

15. Change the coils – we all know they are problematic

16. Change the MAF - the ECM does not receive proper air mass reading

17. This is a very last thing you should do – replace the ECM (ECU)

This is not an exhaustive list but should give you a good start at it. I went through all these steps in troubleshooting my problem and at last I shook the oil-catch canister (on advice of my fiancι ) to find out that the canister itself was leaking at its base and as such drawing in air and was tripping my O2 sensor. I had never thought to look there and was the cheapest thing I had to replace, d'oh. I did all these things except for the ECM replacement including 2 sensors, coils, MAF, plugs. What an expensive way to learn...

Larrio

iTrader: (10)

correct me if i'm wrong....

but bank 1 sensor 2 indicates a secondary o2 sensor and is only there to monitor catalyst efficiency. Therefore, that secondary o2 sensor has nothing to do with your fuel trim adjusts and such in the engine. Hence people can run o2 simulators to fool the ECU into thinking the your vehicle still has precats

If you use a multimeter to check your secondary o2 voltage, you'll see that it oscillates in voltage frequency whereas your primary o2 sensors (sensor 1 on bank 1 or 2) will adjust accordingly, detecting and altering your fuel trim

igzy

iTrader: (18)

It is true that secondary sensor is responsible only for monitoring if the system is running rich or lean (which is what P0140 points to) and primary sensor is responsible for fuel trim management.

Yes, you can by-pass the sensor by installing a simulator, but I would do that only for a faulty sensor replacement and given that everything else runs fine. In cases where other things are wrong, like a vacuum leak in my case (which also raises your idle and RPM at all levels and screws up your consumtion) or bad MAF, I prefer to fix the root cause of the problem rather than installing a simulator...

sloppymax

iTrader: (8)

secondary o2s only monitor and do not affect a/f in any way. only the primary o2 sensors and maf do that under partial throttle and the maf takes over on WOT.

igzy

iTrader: (18)

It is what I said too

Secondary - monitor fuel/air
Primary - manage fuel/air

sloppymax

iTrader: (8)

my fault, i must have read it incorrectly.