Hey all,

My brother purchased a 99 s70 for the wifey recently and the dreaded check engine light has come on. A quick trip to AutoZone reveals a generic code p0030 which has some thing to do with the heated oxygen sensor (the precat sensor, I believe). I apologize in advance for the long post, but want to give as much information as possible to better aid in correct diagnosis, as well as help others out with similar problems.

I bench tested the factory o2 sensor using the propane torch/multimeter approach, which gave me no output. It was probably the original part and there's over 100k miles logged on the clock. After some quick readings with the multimeter, I was able to locate what I believe to be the signal wire (red on the factory sensor). With the key in the on position, that was the only wire out of the five coming off the sensor that was dead (not even a ground). Out of the others, two read 12 volts, and two read 2.5 volts. If I remember correctly, the grey and black showed 12 volts and the yellow and white showed 2.5.

We were able to locate a cheap one wire universal online, but it turned out to be bad, right out of the box. A local parts store had a universal 4-wire Bosch in stock, so we decided to give it a try. After the bad experience with the first universal, I bench tested the new one, which tested fine.

I connected the signal wire (black) on the universal to red on the old harness, and connected the heater wires (whites) to the grey and black. I'm assuming 12 volts is used for the heaters since I have no reason to believe it would be 2.5 volts. (Trying to "ohm" out the wires on the old sensor got me nowhere either.) I did not connect the ground wire (grey) nor the yellow and white on the old harness.

Once it was all installed, we reset the light by pulling a fuse under the hood, and went for a test drive. We drove around for a little over 20 minutes, including some highway without the light ever coming on again. However, the next time we started up the car, the light was back on again.

Now, I know that the old sensor was bad and in need of replacement, which we did, but I'm not sure where to go from here. I don't believe the etc or mass air flow sensor would give this code (someone please correct me if I'm wrong). I've checked for vacuum leaks as well but have been unable to turn up anything there either. I wish repair manuals were a little easier to come by. I don't know if there are any relays or modules I need to have checked? Is there anyway to check if the etc "warranty" has been done?

Thanks again for reading and any help you can offer is appreciated.

 

We went through the same thing at work. In the end ended up replacing both O2 sensors. That is what fixed the problem.

These cars don't like universal sensors.

Also is it Turbo or Non?

 

Thanks for the info, tech. I'll let him know. It's the turbo model.

 

Ok also check for a vaccum leak in the induction hose just before the turbo. There is a valve check where it goes into the pipe.

 

Okay, will do. Thanks again for all your help.

 

I have the same code in my 2000 V70. (in fact it was coming up twice. Does this mean 2 sensors are gone?) It is running really sluggishly. My mech put another MAF meter in this morning and it removed the suggish symptoms. The one he put in is not new, he just had it lying around, and as it fixed the symptoms, he is putting a brand new one in tomorrow. Is it likely i am going to need new o2 sensors as well? Could these code be thrown by the MAF? Why would the symptoms be gone after changing the MAF if it really the o2 sensors? Its been happening since i jump started it last week. I probably fried something.

 

Let me start out by saying I'm no expert, and have limited experience with Volvo's, so take my advice accordingly. I'd say it's possible. If the MAF was reading incorrectly, (low), then the pcm may be leaning out the fuel mixture. When this happens, the o2 sensors read too much oxygen content, and the pcm may be overcompensating with too much fuel delivery. Then the cycle begins again, causing the sluggish condition you describe. The obd2 may then falsely diagnose this as a faulty o2 sensor.

I wouldn't think that a jump start would cause this, probably just a stroke of bad luck. If the check engine light has gone away, and the sluggish running has also dissapeared, you're probably in the clear. Remember, if there is a code, it won't pop back up until after 2 more driving cycles. If the code does come back up, don't use universal o2 sensors, Volvo's don't like them.

I haven't been here for a while, because a short while after clearing the check engine light, thanks to the great folks here, my sister-in-law was t-boned by some kid with a suspended license, totalling the car.
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My experience with Volvo's is limited, so take my advice accordingly. My twisted logic tells me it's possible that the MAF could throw that code. If the MAF sensor read incorrectly (low), then the pcm would only allow a limited amount of fuel delivery. This would cause the o2 sensors to read too much oxygen, causing the pcm to compensate by enriching the fuel mixture. This sluggish running rich/lean cycle created by the MAF may then be misdiagnosed by the obd2 as a lazy (faulty) o2 sensor.

If the check engine light has been remedied, and the sluggish condition has disappeared, I'd say you're probably in the clear. Remember if the light is going to come back, it won't do so until after two driving cycles. If it does come back, don't use universal o2 sensors- Volvo's don't like them.

I'd probably be here more often, but shortly after clearing the codes, (thanks to the great folks here), my sister-in-law was t-boned by some punk kid with a suspended license, totalling the car. It's a good thing for him I wasn't there.
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