2002 Base v70 / CEL codes P0420 & P0328

Mr. Detail · Post by **Mr. Detail** » 16 Sep 2026, 14:55

Hi again guys. Hope you had a great summer!
My older v70 with 228k miles on her gave me a couple of CEL's today. (P0420 & P0328)

P0420 after looking it up says it could be the CAT converter (Bank 1) or possibly a bad Mass Air Flow sensor.
Should I look into replacing the MAF sensor first? I am pretty sure the price of that CAT converter is up there.

P0328 after research, says it is the Bank 1 knock sensor causing that code. Do I need to replace that also or is it
possible that the P0420 is causing the other code to come up.

Many thanks as always for your help.

Post by **chrism** » 16 Sep 2026, 19:43

P0420 refers to cat converter efficiency which is derived from information received from the downstream O2 sensor. I’ve read that the O2 sensor signal is ignored for the first couple minutes after starting a cold engine (when the engine is running super rich). An interesting experiment would be to clear the codes then start the cold engine and let it run about 30 seconds. Shut it off and scan to see if P0328 appears. If P0328 DID appear during that short engine run then I would be inclined to look into the knock sensor first.

Post by **vtl** » 17 Sep 2026, 05:17

If your 2002 runs on factory-installed oxygen sensors, they are both overdue. Replace them every 150k miles or 10 years.

Post by **vtl** » 17 Sep 2026, 05:20

I checked my old records: the base 2002 V70 I had back then asked for the front sensor in 2016, at 145k miles.

Mr. Detail · Post by **Mr. Detail** » 17 Sep 2026, 07:09

Gentlemen, would a factory installed oxygen sensor or OEM be considered a Bosch one?

Mr. Detail · Post by **Mr. Detail** » 17 Sep 2026, 07:10

Also does the naturally aspirated 2.4L engine like mine have just 2 sensors?

Mr. Detail · Post by **Mr. Detail** » 17 Sep 2026, 07:15

chrism-
No codes after running your 30 second test just now.

Post by **vtl** » 17 Sep 2026, 07:19

Mr. Detail wrote: 17 Sep 2026, 07:09 Gentlemen, would a factory installed oxygen sensor or OEM be considered a Bosch one?

Depends on who made the ECM. Bosch for Bosch, Denso for Denso, Siemens for Siemens. Run your car by FCP website.

Post by **vtl** » 17 Sep 2026, 07:24

Mr. Detail wrote: 17 Sep 2026, 07:10 Also does the naturally aspirated 2.4L engine like mine have just 2 sensors?

Yes. Upstream sensor for close-loop air-fuel mixture, downstream sensor for CAT health monitoring. The upstream one usually goes bad first, but the downstream sensor may light up a cat efficiency error sooner than ECM understands the upstream sensor lies. Volvo's CAT is top-notch, fully metallic, hard to kill, unless owner tried hard.

The oxygen sensor related errors are registered after 3 consecutive engine starts and following detection of the sensor failure.

Mr. Detail · Post by **Mr. Detail** » 17 Sep 2026, 11:50

My original ECM went bad I think back in 2023. My local Indy Volvo mechanic replaced it with a re-manufactured Volvo ECM. That one lasted less than a year and it was under warranty, so they gave me a new re-man for no charge.