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Canuck Tech
Canuck Tech, Auto Service Technician
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Experience:  Red Seal Journeyman Technician, 20 Years experience
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Volvo 960: Hello I have a question about my 1997 volvo 960.When

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Hello I have a question about my 1997 volvo 960.
When I connect OBD 2 tester, it tells that fuel 1 CL- fault
And, the rear oxygen sensor(B1S2) seems not working because the voltage is 0.

The history is like this.

last week, once the readiness cycle was done and, at that time, it came up engine check light that tells rear oxygen sensor is not working, the code is P0141.

So, today I changed the rear oxygen sensor but, seems not working...

please give some advise, Is there any relation between readiness cycle and these problem??

Thank you
The car won't pass the readiness cycle if the computer is not satisfied that the sensors are not working properly... I can give you a few more details on how this works shortly... In about an hour and a half, if that is OK - gotta get into the office. Canuck.

One of the main reasons the rear oxygen sensor is there is for doing the catalyst efficiency test. The engine computer monitors the front oxygen sensor, and expects it to switch between approximately 100 millivolts and 900 millivolts. If the catalyst is functional, the rear oxygen sensor should be relatively flat in its output, but not at zero volts.

The catalyst stores and releases oxygen - this is why the output is not variable like the front o2 signal. So, if the car is warm, and the rear o2 sensor output is stable (but not 0) the cat is functioning. If it stays low all the time, this could indicate a lean running engine, but I think there would be other symptoms, like a P0171 code.

Are you trying to pass an emissions test, or are you seeking general information? Canuck

Customer: replied 4 years ago.

I'm trying to pass CA smog emission test!
I already taken to there 10 times, and every time I was said that I need keep driving to finish the readiness cycle.

I drove about 1500 mile, and then it seems the readiness cycle was finished, but at the same time, engine check light came up(p0141)
When I checked the oxygen sensor, the wire was torn, so I replaced it.



OK - is the Check Engine light on now?

Customer: replied 4 years ago.

no, I cleared the Check light.

I hate to say it, but you need to drive it again. Can you check Readiness Tests with your scanner?
Customer: replied 4 years ago.

I can check the sensors such as o2, cat, etc blinking or not. I'm using innova 3130. After stop blinking, I think the readiness has done.

Now I'm worried that whether the rear o2 sensor is working or not.

Before I changed the torn oxygen sensor, the engine check light did not come up until I finish the readiness cycle, even though it was broken!

So, I'm worried about being same situation that the rear sensor is not working, and waste time.

I understand your concern. If I understand you correctly, you could look at the rear oxygen sensor voltage to determine whether or not it is working. If you were to hook up the scanner, and start the engine cold, the oxygen sensors would start working in about a minute. The voltage on the front sensor should vary between .100 volt, and .9 volt. The rear should do the same, until the catalyst starts to get warm, at which point the rear oxygen sensor should move less, and be much more stable. Let me look at the innova tool website to check out that tool... Canuck
There should be a green LED that comes on by the I\M label. Green means the monitors have run
Customer: replied 4 years ago.

After I drove hour, the rear oxygen senser seems to be working because the STFT B1S2 vary between -10% and 90%. However, the B1S2 voltage doesn't change, it stay 0 voltage.
What can be guess from this??

On board diagnostics regarding European cars can be a little tricky, and I am going on experience here... Even though there is supposed to be a common communication protocol between the scan tool and the vehicle, it is entirely possible that the car is working fine, but there is a glitch in the scanner software that is causing the rear O2 sensor to read zero.

With the scan tool you have, you are somewhat limited... and honestly, you may need to take a trip to the Volvo dealer if you want to make sure the readiness tests have run.

I feel your frustration trying to pass CA emissions... but I don't know of another way around this... Obd II is complicated, and without boring you with unnecessary details, it is a progressive diagnostic system. As an example, the front O2 sensor must pass a heater test and then an operation test. Next, the rear O2 sensor must pass the same tests. But there is very specific criteria for these on board tests, and the vehicle has to be operated in a certain manner for the test to run. I looked up the code you supplied, and guess what? There was no information as to what it takes for that rear O2 sensor diagnosis to run! AGGGGHHHH!

Moving along, once the oxygen sensors tests have run and passed, then the catalyst diagnostic needs to happen - catalyst efficiency... and so you see it takes a while for the car to run its diagnostics and set the Readiness Monitors.

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