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DIY: Do It Yourself
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Old 06-14-2013, 03:56 PM   #1
MisterF
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Join Date: Jun 2013
Location: Pennsylvania
Posts: 30
My Ride: 330i
Dreaded p0420 code thrown after replacing fuel filter/pump

Hey, guys, I'm new to the community. I've been a lurker for a few years now as I've done a few DIY projects replacing old parts on my car, but the past couple of weeks have been quite stressful as I'm trying to balance my life and figuring out what's wrong.

My fuel pump went out not too long ago, so I replaced my filter and pump, but right after I did that, the p0420 code was showing after a few car starts. I've tried using BMW Scanner 1.4.0 to reset the adaptation, and it was fine for a week, but my SES light came up again today. I've done a lot of searching every day during most of my spare time to find out common problems and fixes. So here I am today, asking for help.

I don't have the tools to diagnose the emissions and o2 sensors, so if it's most likely that or the cats, I'm going to take it to a shop. I just want to see if there's any common problems involving replacement of the fuel pump/filter and the code.

TL;DR -- Fuel pump died, replaced it and fuel filter. P0420 shows right after replacement. One post cat o2 sensor already been replaced recently, but the other one hasn't. I have 123456 miles on it, just hit last night.

Here's what the BMW Scanner tool showed before I cleared all codes and reset adaptation. From what I understand, cats are supposed to be really durable, so I'm also trying to figure out what could be causing it to go bad, if it is the cat that has gone bad. Hoping it's just an o2 sensor.

DME -> F6/B8 - Secondary air system, flow rate too low, bank 2
F5/B8 - Secondary air system, flow rate too low, bank 1
E4/B1 - Oxygen sensor controller, bank 2, deviation too great, deviation rich
E3/B1 - Oxygen sensor controller, bank 1, deviation too great, deviation rich
CB/B1 - Oxygen sensor control, bank 2, control limit, mixture limit rich
CA/B1 - Oxygen sensor control, bank 1, control limit, mixture limit rich
EE/B2 - Misfire, cylinder 1, misfiring during warm up, worsening emissions (Misfire CARB_B1)
F1/B2 - Misfire, cylinder 4, misfiring during warm up, worsening emissions (Misfire CARB_B1)
E9/71 - Catalytic converter efficiency too low, bank 1
Shadow-memory:
F6/B8 - Secondary air system, flow rate too low, bank 2
F5/B8 - Secondary air system, flow rate too low, bank 1
E4/B1 - Oxygen sensor controller, bank 2, deviation too great, deviation rich
E3/B1 - Oxygen sensor controller, bank 1, deviation too great, deviation rich
CB/B1 - Oxygen sensor control, bank 2, control limit, mixture limit rich
CA/B1 - Oxygen sensor control, bank 1, control limit, mixture limit rich
EE/B2 - Misfire, cylinder 1, misfiring during warm up, worsening emissions (Misfire CARB_B1)
F1/B2 - Misfire, cylinder 4, misfiring during warm up, worsening emissions (Misfire CARB_B1)
E9/71 - Catalytic converter efficiency too low, bank 1
5A/12 - Exhaust temperature before catalyst, bank 1, signal line, short circuit to negative
5C/12 - Exhaust temperature after catalyst, bank 1, signal line, short circuit to negative
5B/12 - Exhaust temperature before catalyst, bank 2, signal line, short circuit to negative
5D/12 - Exhaust temperature after catalyst, bank 2, signal line, short circuit to negative
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Old 06-23-2013, 12:08 AM   #2
MisterF
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Join Date: Jun 2013
Location: Pennsylvania
Posts: 30
My Ride: 330i
Would it be a problem if my battery was dead for like 3 days while I was working on replacing the fuel filter/pump? Battery might have been dead for a while, I was out of town....I replaced the filter first, then tried to jump start it, but failed, finding out the pump is shot. Then I replaced the pump then jump started it. A couple of starts later, the p0420 showed up. Would disconnecting the battery for 20 minutes reset adaptations that the BMW scanner can't?
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Old 06-24-2013, 06:19 PM   #3
MisterF
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Join Date: Jun 2013
Location: Pennsylvania
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Alright, I'm just going to take it to the shop and replace the post cat bank 1 o2 sensor. I did the bank 2 already a few months ago. I have a leaking oil filter housing gasket that needs to be replaced, too, anyways. Anyone know if replacing the fuel filter or fuel pump could cause a p0420 code to show up due to sudden change in fuel flow or something? I'm wondering if the problem is in the computer or is something physical. Regardless, I need to take care of it this week because my emissions test is due.
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Old 06-24-2013, 09:11 PM   #4
BMARTINW
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Join Date: May 2013
Location: San Diego
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My Ride: E46 S54 SALOON
SPARK PLUGS! Trust me I had the same issue, replace them with the NGK R's double platinum, they look like the Bostch platinum 4's, and look for the little plug in back of the intake manifold,it's just a little cap on the back you could see it with the cabin filter off it might still be there but cracked, some Teflon on tape in the middle will seal it right up again, you should be good and clean your MAF

Last edited by BMARTINW; 06-24-2013 at 09:13 PM.
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Old 06-24-2013, 09:17 PM   #5
MisterF
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Join Date: Jun 2013
Location: Pennsylvania
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My Ride: 330i
Alright, I'll check my spark plugs, but my dad and I just replaced them 23k miles ago. One of my ignition coils did go bad last year, and I had to replace that. I'll also look for this plug you're talking about. What is it for, and why could it be causing a p0420 code? Did your problem also come up after replacing the fuel filter and pump? I seriously thought it was going to be a temp code from the job, but it ended up hanging around.

Last edited by MisterF; 06-25-2013 at 03:23 AM.
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