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Discussion Starter #1
I'm getting a 0420 error on my 08 Outback, which is probably a sensor on the exhaust system. But the twist is that when it happens, it disables my Cruis Control. The Check Engine light comes on and the Cruise light blinks and is disabled until the code is zero'd out. Then it's fine for a few days or a month but it always comes back. I figured out that the Cruise and Exhauset sensors are on the same system and replaced the main relay for it, but it only lasted a couple weeks then got the error again. Any ideas?
 

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2004 Outback Wagon, 2.5, 4EAT, All weather package.
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1,040 Posts
By design, the car is supposed to disable the cruise control when the check engine light is on.
 

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I simply cannot abide useless people.
2006 2.5i and 2002 3.0 wagons.
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12,306 Posts
1: A CEL automatically disables the Cruise. It's how they get people to actually pay attention to them.

2: That code is most commonly a failing oxygen sensor, or leak in the intake/exhaust. RARELY the cat.

3: Thread moved to correct forum.
 

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2001 VDC/SC One of a Kind
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14,436 Posts
How many miles on the car?

I have a customer with an 08 Impreza that has had 2 CATS in 80k miles. I can never find what made the CAT fail other than just a crappy CAT with a short lifespan. Both times the CAT came from Subaru.

And they did that with the Cruise so you wouldn't ignore it and make things worse.
 

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1993 Legacy LSi with still functioning Air Suspension, 1999 Outback 2.5L 5MT lab Rat
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191 Posts
The cruise on your car is part of the electronic throttle control, which is why when any engine code occurs Cruise Control is disabled. P0420 code is more than likely a failed Catalytic Convertor, or with the Fed Government now allowing 15% ethanol blending in Gas a potential intermittant False fail. Cars are designed to run the predominant blend at time of manufacture but if the Fed changes blending rules, its tough to account for that after the vehicle has reached the service stream (ownership)Check with your local dealer about potential ECM software updates that may be available as well as potential warranty replacement under the PZEV warranty. Cat. Converters are Spendy $$$
 

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2001 VDC/SC One of a Kind
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14,436 Posts
The cruise on your car is part of the electronic throttle control, which is why when any engine code occurs Cruise Control is disabled. P0420 code is more than likely a failed Catalytic Convertor, or with the Fed Government now allowing 15% ethanol blending in Gas a potential intermittant False fail. Cars are designed to run the predominant blend at time of manufacture but if the Fed changes blending rules, its tough to account for that after the vehicle has reached the service stream (ownership)Check with your local dealer about potential ECM software updates that may be available as well as potential warranty replacement under the PZEV warranty. Cat. Converters are Spendy $$$
http://www.subaruoutback.org/forums/66-problems-maintenance/49537-p0420-diag.html

Forget what you may have been told about a 420 automatically being the CAT. Yeah, high alcohol blends and the winter blend with the oxygenated agents and anti gels effect the WB sensor and rear O2 sensor outputs to the ECM. The car may think its running lean with winter blends. Higher alcohol content is adjusted through injector pulse to add more fuel. The computer doesn't know the alcohol level, it only adjust the pulse according to the WB data. And, since its an 08, and I don't change CATs very much because its generally something else with engine performance, I have installed 2 CATs on the same car in 80k miles and all the engine performance checks out, all sensors operating properly and the ECM had the latest software updates on a 2.5 SOHC and maintenance was by the book. The owner was running crappy Wal Mart and a grocer shelf blend until the last CAT was installed, so that could have been a major factor.
 

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06 Outback 2.5i, 05 Outback Limited
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So... umm... my cruise isn't supposed to work with CEL on?

P0420 for the last year and a half.... cruise works fine...
 

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2001 VDC/SC One of a Kind
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So... umm... my cruise isn't supposed to work with CEL on?

P0420 for the last year and a half.... cruise works fine...
Yours is cable driven with a CC module running a second cable. The 05 up use electronic throttle control. The throttle position and CC are all run through the electronic unit.
 

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06 Outback 2.5i, 05 Outback Limited
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868 Posts
Yours is cable driven with a CC module running a second cable. The 05 up use electronic throttle control. The throttle position and CC are all run through the electronic unit.
Oh. Thanks, doc :)
 

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Discussion Starter #10
Thanks for all your help everyone! The car has about 50k on it now. I tend to drive up to Iowa quite a bit where they have the ethanol blend at the pump. I do try to support the farmers so I always buy it. Could that be causing my trouble? It ran fine for about a month when I was running on non-ethanol blends.
 

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I simply cannot abide useless people.
2006 2.5i and 2002 3.0 wagons.
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12,306 Posts
By ethanol blend do you mean E10 or E85?
 
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