Last November I saw the check engine light come on, right before the car registration was due. I thought this would drain my pocket, but luckily I found a supercharger install video, it helped me decide that I would do it myself (I included the link to the video below).
Not sure this caused the problem, In October 2024, I added a quart of oil, because I saw the oil level slightly less than usual. And, I must say here Volvo should show the amount of oil in gallons or quarts in the digital output.
Anyway, here is my experience, I hope this helps someone.
Observation
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1- Obvious check engine light, OBD code P0171, “and only P0171”.
2- Once the car did hesitate when leaving the gas station, the check engine light was on for almost two days. it felt that the engine was having trouble idling.
3- The OBD reader shows, the oxygen sensor bank 1 output was between .9 to 1.01 (I think the unit is volts but the OBD reader does not show the unit).
4- MAF sensor output 2.66 g/s at idle, 11.37% engine load, a new MAF did not solve the problem.
5- Occasional misfire observed in OBD reader data stream, only on startup, but was not noticeable.
6- Filled engine coolant once in two years, zero coolant leaks so far, I checked.
7- Oil leak from the drain plug, lucky.
8- All Spark plugs looked barely used, cleaned and reinstalled.
9- Intake smoke test shows smoke between the intake and the supercharger, but only when the engine is cold.
How to Fix this
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1- Replaced PCV oil separator box, Diapharagm was broken, mostly likely due to repeated removal of the pcv cap, self-inflicted, Part#32140004.
2- Tighten oil cap gasket using Teflon tape, I didn’t need to but I did this before using a smoke machine. A simple DIY, don’t need to purchase a new gas cap.
2- Cleaned the PCV valve, the valve was clogged and used non-chlorinated brake cleaner.
2- Cleaned and re-installed spark plugs, checked for gasoline oil burn signs, no ash, all dark, all good.
3- Air intake connection with Supercharger, (replaced some seals, which I believe I didn’t need to replace). The bottom screws connecting the air intake to the supercharger were loose.
4- Replaced Bank 1 Oxygen sensor, I don’t believe the oxygen sensor was bad, see the pic. But replacing the Oxygen sensor did fix the issue, the new O2 sensor purchased was, Denso Part#234-9160.
Tools purchased
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1- Universal O2 sensor socket 7/8 O2, 3/8 inch drive.
2- 15mm wrench, preferably a 12in long handle, I couldn’t find a 12in long wrench, did all the work with a 9in. This is for releasing the belt from the supercharger, make sure to buy one with an anti-slip design.
3- Torx bit set, T40, T30 and T25, for supercharger work.
4- TOPDON TopScan OBD reader/writer, this did not help much other than clearing the code. I was hoping to find a smoking gun, but OBD readout of the new oxygen sensor was the as the old one.
5- Automotive Smoke Machine & smoke oil.
Preventative maintenance
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1- Periodically clean the PCV valve and oil separator, probably around every 10K to 20K miles.
2- Always fill oil with 4 quarts, no more, no less.
3- At every oil change look for oil leaks, and always look for the source.
4- Watch for the fuel trim ratio, may reveal more, but I have to do more investigation.
The most likely cause of the lean condition
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1- Clog PCV oil valve, started a chain reaction that eventually led to the lean condition.
2- Slow oxygen sensor, the oxygen sensor was either already bad/slow or was bad/slow from the lean condition.
3- Loose air intake connection with supercharger. I am not sure which one happened first, the bad oxygen sensor or the loose air intake connection, But one thing is for sure in almost every Volvo T6 supercharger video I observed that the bolts were loose, causing the gap between the intake and the supercharger.
4- Less driving, I read in one of the forums that shorter distances allow oil accumulation in the PCV oil separator box, which eventually leads to clogging.
Resources
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1- This video helped in understand the work required to remove and install the supercharger.
2- Sweed speed forums and other forums helped me understand the variables that can cause this problem.
*I hope now that I had this runs past 100k.
This is the picture of the old Oxygen sensor.
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