Yes! This is what happens exactly.
I have measured the resistance of the heater - about 4 ohm.
Is that OK?

 

Yes, that is a fairly accurate reading for a good heater.

 

Hi, I'm still waiting for the new sensor.
I have checked the bank 1 sensors:




The upstream is with a gray connector, two black wires for the heater, white and blue wire for the signal. It's not lambda, but a current sensor, right?
The downstream is with a black connector, two white wires for the heater, black and pink for the voltage signal.

At the back of the engine are the bank 2 sensors:


The upstream is the same as in bank 1 - grey connector, two black wires for the heater, white and blue wire for the signal.
The downstream is again with a black connector, but the wires are like at the upstream - two black wires for the heater, white and blue wire for the signal..
Is this normal?

 

2v6, O2 sensors are a current sensor per se. What they are trying to do is keep the sensor a finite amount of degrees above the exhaust temp. This is done by heating up the sensor. Because of the materials used in the sensor, as oxygen flows past the sensor, it cools off the sensor. Therefore, the more oxygen that goes by the sensor, the more it is cooled, the more current that is needed to warm it back up to the finite degrees above the exhaust. But, most people see a voltage reading (just the current passed through a resistor resulting in a voltage across the resistor) is what you see. People understand voltage easier than they do current.

As for the wire colors on the sensors, I would not get too caught up with that. Technically, a supplier can put whatever color wire on a device that they want. Now, most have agreed to a standard (ie, 2 black wires, a blue, and a white), but just when you think they all did that, nope, you get one where they didn't. hence why a lot of people tell you to refer back to the factory wiring on the other side of the connector. That remains constant unless you get someone to make a repair and they don't match up the wiring.

 

Maybe I have a wrong explanation in the previous post - so Bank 2 sensors are in the front of the car (engine) or in the middle of the car (back of the engine)?

 

2v6, bank 2 is on the front of the car, under the air box. Bank 1 is on the side of the engine facing the firewall. It gets a little confusing with a transverse engine because there is no real left/right side which is how most people describe things.

 

Thanks for the clarification Thermo!

What will happen if I "exchange" the upstream and downstream sensors? Just connectors place.
Are the sensors the same type?

 

No
The upstream sensor is the one before the catalytic converter. Downstream is the one in the catalytic converter. Upstream reads air/fuel mixture and sends signal back to engine control unit to adjust fuel mixture. The downstream sensor simply determines if the catalytic converter is working correctly and not clogged or burning out.

 

Hi Dell Gailey,

I believe that the catalytic converter is missing.
So in this case is it possible to exchange the connectors?

 

2v6, if you don't have a cat in the car between the two sensors, then, that would explain why you are getting an error code. The computer is looking for a difference in the oxygen levels between upstream and downstream sensors. Can you reverse the sensors for a quick check to see if the error moves. Sure. You are not going to hurt anything. But, this WILL cause an error code to happen (now the car sees the downstream O2 levels higher than the upstream levels). Hopefully what I just said will answer some questions that you have been pondering and make sense of what you are seeing.

 

Old thread but I missed it the 1st time around so thought I would throw in... If your catalyst inside the converter is missing as was suspected the upstream and downstream O2 sensors will move in sync. Same changes at the same time (or separated by a small fraction of a second). This will cause the car to throw a P0420 or P0430 code "catalyst system efficiency below threshold". P0420 is Bank 1, P0430 is Bank 2. I bought my car with that error thinking it was simply a bad O2 sensor. Turned out to be a catalytic converter that was completely empty.

 

Not easy to see as upstream & downstream are very different technology O2 sensors (wideband & non-wideband).

 

Quantitatively yes, different units but qualitatively the downstream sensor should be very steady compared to the upstream. If they are both working and both signals are changing at the same frequency you have a problem. That is my understanding. I was pretty shocked when I compared the downstream O2 sensors between bank 1 which had an empty tube where there should have been catalyst and bank 2 which had a good cat. One signal changing several times per second and one barely changing at all.

 

With wideband the upstreams should be steady.

The upstreams simply do not do that when wideband.

You seem fixated on both upstreams & downstreams behaving as if the same technology - but they aren't.

 

I am fixated and I appreciate your patience trying to set me straight. I understand the technology is different for the wideband sensors. They are measuring air/fuel ratio and not just a too rich or too lean switch. Sensor output is a varying current not voltage. The piece that I am hung up on is the input to the O2 sensor is the same regardless of sensor technology: A/F ratio changes due to various engine conditions that requires the O2 sensor feedback to the ECU. The ECU is making A/F adjustments many times per second based on O2 sensor feedback regardless of what type of O2 sensor is used.

The graph below is sensor current as reported to the OBD by my wideband sensor upstream of the catalyst on bank 2 of my 2005 X-Type when I drove to the grocery store yesterday. Also below is the ECU's interpretation of what that means in Air/Fuel ratio taken from the OBD. The sensor output level is low but I wouldn't say either the sensor or the A/F ratio computed using the sensor is steady. Steady being relative of course.

 

The upstream sensor is situated before the catalytic converter whereas the downstream oxygen sensor is located after the catalytic converter. The upstream sensor monitors the level of pollutants in the engine's exhaust and sends this information to the ECU that continuously adjusts the air-fuel ratio. The downstream sensor measures the level of pollutants passing through the catalytic converter. The information from the upstream and downstream sensors are compared by the ECU. If the readings from the two sensors become more similar to each other, the ECU triggers a catalyst inefficiency code.

Oxygen sensor 1 is the upstream oxygen sensor in relation to the catalytic converter. It measures the air-fuel ratio of the exhaust coming out of the exhaust manifold and sends the high and low voltage signals to the powertrain control module in order to regulate the air-fuel mixture.The voltage generated from the O2 sensor should be from 0.1V to 0.9V, with 0.9V on the rich side and 0.1V on the lean side. When the powertrain control module receives a low voltage (lean) signal, it compensates by increasing the amount of fuel in the mixture. When the powertrain control module receives a high voltage (rich) signal, it leans the mixture by reducing the amount of fuel it adds to the mixture. The powertrain control module’s use of the input from the oxygen sensor to regulate the fuel mixture is known as a closed feedback control loop. This closed loop operation results in a constant flip-flop between rich and lean, which allows the catalytic converter to minimize emissions by keeping the overall average ratio of the fuel mixture in proper balance.

However, when a cold engine is started, or if an oxygen sensor fails, the powertrain control module enters into open loop operation. In open loop operation, the powertrain control module does not receive a signal from the oxygen sensor and orders a fixed rich fuel mixture. Open loop operation results in increased fuel consumptions and emissions. Many newer oxygen sensors contain heating elements to help them get to operating temperature quickly in order to minimize the amount of time spent in open loop operation.

Oxygen sensor 2 is the downstream oxygen sensor in relationship to the catalytic converter. It measures the air-fuel ratio coming out of the catalytic converter to ensure the catalytic converter is functioning properly. The catalytic converter works to maintain the stoichiometric air-fuel ratio 14.7:1 while the powertrain control module constantly flip-flops between rich and lean air-fuel mixtures due to the input from the upstream oxygen sensor (sensor 1). Therefore, the downstream oxygen sensor (sensor 2) should produce a steady voltage of approximately 0.45 volts.