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DTC P2097 Post Catalyst Fuel Trim System High Limit Bank 1
The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio.
Fuel trim biasing is used by the ECM to keep the post catalyst HO2S voltage within a range of 580-665 mV as possible. This allows optimal catalyst efficiency under light load conditions, such as at idle or a steady cruise. The ECM constantly monitors how lean or rich the fuel trim bias is commanded. If the ECM detects that the fuel trim bias is commanded rich for more than a calibrated amount, DTC P2097 or P2099 sets.
You do not have to have the diagnostic light staying constantly on to have an issue with the car. It will be in the ECM's memory if any faults are present, as you said it had a couple of faults. Yes lack of power can be caused by a faulty Oxygen sensor . The only way to check is to hook up your scan tool and put it in live data mode and read the outputs of the sensor. If it's coming up Bank 2 then I take it, it has a Bank 1 sensor as well so compare it to that. Also take into consideration that fuel, spark or air leak can cause out of speck readings as well. Some cars oxygen sensors are the same for bank 1 and 2 so even swapping them around and re checking codes can be a great test. Cheers
Hi Rm. Your problem is with the air fuel mixture control. Carry out an inspection to see if there are any broken intake ducts or broken, cracked or loose fitting vacuum tubes. A defective knock sensor, camshaft or crankshaft pick up sensor could result in your code, but would usually record as a fault on the read out, as would the lambda and oxygen sensors, so have a look for air leaking into the manifold. Regards John
Hi Brad, I think it would be a good idea for you to take the vehicle for a diagnostic scan to a workshop where the technicians know what they are doing. The sensors may not have been the problem, but instead the information they are reading. The OZ sensors are oxygen sensors and read the amount of un-burned oxygen in the exhaust gas after combustion. In other words the fuel injected may be too much and the engine is running too rich, which relates to the high consumption. Try replacing the spark plugs and the air filter, but do take it for the scan. Regards John
your front oxygen sensor/lambda sensor is broken. you need to replace it. it stalls because o2 sensors start to work at higher temperatures(when cold car uses previous know error free mixture ratio - rich mixture). when engine is warmed up, your o2 sensor cant read correct values and engine controller cant decide on required amount of fuel to be burned in chamber.
Not sure, but I believe the lambda sensor is the feedback sensor, to determine if the mixture really is right.
On most cars that is the oxygen sensor I believe, and is located in the exhaust manifold or the top of the exhaust pipe.
P0420 is one of two things, it is either a catalyst failure (below threshold) or rear lambda.
The rear lambda should have a steady waveform when the engine is running if not then P0420 will be stored.
Cats and lambdas are very common on Subaru.
As the car is older than 2001 it does not come under R103 regulations therefore you could cut out the old cat and replace with a Carsound (Magnaflow) universal bullet. That will save you £££
The Subaru lambdas are now available aftermarket so try a motor factor, not the dealers.
If UK email me for info on where to purchase any of the above.
1.The oxygen sensor is located where the manifold comes together and meet the exhaust pipe. 2. The second one would be located after the catalytic converter. Go to this website and you will see an example. http://www.walkerproducts.com/locations.html