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Author Topic: Error Code P420 and timing chain replacement?  (Read 2077 times, 13 Replies)
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rick4675
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« on: May 04, 2016, 08:38:00 AM »

My check engine light recently came on. When I hooked my code reader up to it, I received the P420 (Catalyst efficiency below threshold Bank 1). I immediately thought it must be a problem with the catalytic converter. However, my scan tool gives suggestions for the most common fixes based on vehicle year, make, and model. and it came back as "Replace Timing Chain"! huh?? Does anyone know if a stretched timing chain would cause that P420 code to kick out?? Thanks!
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Speleos
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« Reply #1 on: May 04, 2016, 09:17:54 AM »

That's one of the possibilities - there are many. Best to go to a professional service center if you can't figure it out on your own. It would be good to know what year, model, and mileage you have.
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rick4675
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« Reply #2 on: May 04, 2016, 09:40:19 AM »

Sorry, you're right about knowing the vehicle info. I have a 2009 Acadia with approx 92K miles.
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Speleos
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« Reply #3 on: May 04, 2016, 10:39:28 AM »

If the vehicle has a stretched timing chain issue, it can be repaired under SCA #11340B - Timing Chain Wear. This Agreement (essentially a warranty extension concerning a specific item) is good for 10 years/120,000 miles, whichever comes first, regardless of ownership. Look at the 'Recall' thread (http://www.acadiaforum.net/index.php?topic=10487.0) and others concerning stretched timing chains for details.
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2007 Acadia SLT-2, HiYo Silver/Titanium, no NAV, no HUD, no errors - SLT-2 Club #2 (I try harder), Silver Club #4
2009 Toyota Matrix S, Nautical Blue Metallic
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« Reply #4 on: May 04, 2016, 10:46:22 AM »

Thank you. I will look into that. I am still confused as to how a timing chain issue would kick out the P0420 error code though!  shrug
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Speleos
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« Reply #5 on: May 04, 2016, 11:23:08 AM »

In a nutshell ... Valve timing is one of the things that effects the way fuel is burned. Catalytic converters don't really like unburned fuel passing through them. After a while, they become inefficient at handling the unburned fuel. What surprises me is that there aren't any other fault codes present.  shrug
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2007 Acadia SLT-2, HiYo Silver/Titanium, no NAV, no HUD, no errors - SLT-2 Club #2 (I try harder), Silver Club #4
2009 Toyota Matrix S, Nautical Blue Metallic
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« Reply #6 on: May 04, 2016, 01:37:36 PM »

The absence of other fault codes surprised me too after doing a bit of online research. I will just take it over to the dealer and see what they come back with.
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Craigs2010SLT
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« Reply #7 on: May 04, 2016, 03:48:39 PM »

FWIW, I saw a similar situation with my 2010 at 125,000 miles.  P0420 occurred with timing chain code P0008 (Bank 1 Engine Performance Inefficiency).  P0420 was eliminated by replacing all six coil packs. After 6+ years of continuous use, there was no point in replacing less than six.  Coil packs performance can deteriorate, like everything else.  Inefficient coil packs will also contribute to and magnify poor combustion.  In my case, at least with new coil packs, the unstable idle that accompanied the P0008 was improved.  Coil pack fix - relatively cheap DIY; timing chain replacement - painfully expensive.  So yes, P0420 and P0008 can occur at the same time. Good luck!
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« Reply #8 on: May 05, 2016, 04:53:59 PM »

I, too, just had my timing chain and catalytic converter replaced due to codes P0008 and P0420 about a month ago. My 2010 had about 93,000 miles on it.

I hope I didn't just pay to have the CAT replaced for nothing and the real issue is the coil packs as was the problem with Craig's.
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« Reply #9 on: May 05, 2016, 08:32:10 PM »

Kingsfr - As part of diagnosing the P0420, I looked at the output from the O2 sensor on the Bank 1 CAT using my Flukemeter (has a basic scope function). Clearly, the upstream sensor was performing less than ideal, so it would have been easy to conclude that the CAT was faulty.  However, my approach was to rule out poor combustion first.  Also, a new GM CAT costs a small fortune, so no need to jump to conclusions too early.  Plugs were due for replacement, so it was a good place to start - didn't rectify the P0420, but it did run better.  When the coil packs were replaced, the idle settled down considerably and the P0420 code vanished.  Re-checked the output and waveform from the Bank 1 O2 sensor and it was perfect.  I'm certain that a few CATs have likely been prematurely replaced due to shortcuts in troubleshooting.  In my case, it was unneccessary.  The scope offered irrefutable evidence that this was the 'right' fix.
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« Reply #10 on: May 07, 2016, 08:07:29 PM »

Kingsfr - As part of diagnosing the P0420, I looked at the output from the O2 sensor on the Bank 1 CAT using my Flukemeter (has a basic scope function). Clearly, the upstream sensor was performing less than ideal, so it would have been easy to conclude that the CAT was faulty.  However, my approach was to rule out poor combustion first.  Also, a new GM CAT costs a small fortune, so no need to jump to conclusions too early.  Plugs were due for replacement, so it was a good place to start - didn't rectify the P0420, but it did run better.  When the coil packs were replaced, the idle settled down considerably and the P0420 code vanished.  Re-checked the output and waveform from the Bank 1 O2 sensor and it was perfect.  I'm certain that a few CATs have likely been prematurely replaced due to shortcuts in troubleshooting.  In my case, it was unneccessary.  The scope offered irrefutable evidence that this was the 'right' fix.

I wish I knew more about the diagnosing as you do. Unfortunately, I have to rely on mechanics.
I guess I'll just have to wait and see if the code comes back.
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« Reply #11 on: May 08, 2016, 10:40:55 AM »

For a cat to operate at peak efficiency it needs a relatively clean exhaust sample form the engine provided by good fuel management. When the O2 sensor gets lazy, it is not doing its part to tweak the air/fuel mix, the cat can't handle the extra fuel,  and the PO420 code sets. Why an O2 code wasn't set is likely because its just not bad enough yet to do so. Some believe that if this is the case, then the cat is getting old and not as efficient which it likely isn't if a high mileage vehicle. However, like said earlier, many cats get replaced that don't need to. Other related possibilities need to be addressed including repairing lower numbered code problems first as they often are what trigger higher ones close in sequence. The cat should be the LAST part to condemn not just because of cost but due to the fact they are designed to last the life of the vehicle.   
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Craigs2010SLT
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« Reply #12 on: May 08, 2016, 01:07:04 PM »

This was a really interesting and worthwhile exercise.  As with any problem, it's so important to find 'ground zero' as to the cause, before changing parts.  It tends to be a lot less costly.  In my case, the CAT efficiency dropped below the set threshold to trigger the P0420 because some other processes upstream were failing.  If I didn't fix the upstream processes first, replacing the CAT would have only been a temporary fix.  It's a leading cause of why at times you see repeated failures of CAT's in some vehicles. A CAT is generally only as efficient as what the upstream combustion processes throw at it.  Don't forget, it sits near the end of the combustion food chain.  As the upstream processes become less efficient, they inflict that degradation on the CAT.  The CAT's job is to clean up the mess caused upstream, but there's a finite limit to what it can tell the engine computer to do, and obviously, it can't restore the wear and tear on the plugs, coil packs, chain tensioners or gunk in the throttle body, etc.
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« Reply #13 on: February 16, 2017, 02:04:16 PM »

FWIW, I saw a similar situation with my 2010 at 125,000 miles.  P0420 occurred with timing chain code P0008 (Bank 1 Engine Performance Inefficiency).  P0420 was eliminated by replacing all six coil packs. After 6+ years of continuous use, there was no point in replacing less than six.  Coil packs performance can deteriorate, like everything else.  Inefficient coil packs will also contribute to and magnify poor combustion.  In my case, at least with new coil packs, the unstable idle that accompanied the P0008 was improved.  Coil pack fix - relatively cheap DIY; timing chain replacement - painfully expensive.  So yes, P0420 and P0008 can occur at the same time. Good luck!

Did you get the p0008 code to disappear too after replacing the coil packs?

...I have these same two codes on my 2011. My engine light will stay on for a while and then periodically go off for anywhere between 0-120 miles and then it comes back on. It seems like moisture might be contributing to the light clearing (not lit) as it seems to coincide with times when the air is really damp or I've run the car through a car wash (odd behavior!!!??!!).
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