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BMW 3-Series (E90 E92) Forum
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Code P0421 and terrible gas mileage
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03-28-2023, 07:38 PM | #1 |
Enlisted Member
21
Rep 36
Posts |
Code P0421 and terrible gas mileage
I have a 2006 330i with a little over 200k miles on it. Car runs great, but a few weeks ago I had my CEL come on and scanned it with a generic OBD scanner. Came back as 'P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)'. I have also been getting really bad MPGs lately as well.
Any idea on what could be going on? I was thinking may O2 sensor? Anyone else have a similar experience with this code? |
03-30-2023, 10:48 PM | #2 |
Brigadier General
2851
Rep 4,322
Posts |
The o2 sensor is cheaper than a new cat converter.
I can’t find which sensor relates to P0421, but my guess is the rear sensor is bad. You can diagnose it with a better scan tool/voltmeter. |
Appreciate
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