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Discussion Starter #1 (Edited)
As I've been b-ching about my continuing check-engine light issue and P0420 code (CEL on over and over, even after some dealer repairs done), I am seeing an interesting pattern.

I am seeing the light come on when I drive slow, especially in a surface-road-speed under 35mph, the typical 1-2-3-2-N-1-2-3-2-N... traffic.

But when I get on the freeway, and REALLY floor the car (hitting the red-light on every gear) on the on-ramp, the light goes away. :)

Is the CEL the car's way of telling me I need to ride "her" hard...? :shrug:


;)
 

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Registered
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9,786 Posts
As I've been b-ching about my continuing check-engine light issue and P0420 code (CEL on over and over, even after some dealer repairs done), I am seeing an interesting pattern.

I am seeing the light come on when I drive slow, especially in a surface-road-speed under 35mph, the typical 1-2-3-2-N-1-2-3-2-N... traffic.

But when I get on the freeway, and REALLY floor the car (hitting the red-light on every gear) on the on-ramp, the light goes away. :)

Is the CEL the car's way of telling me I need to ride "her" hard...? :shrug:


;)
According to the service manual, a P0420 fault (Catalyst System Efficiency Below Threshold) can only be triggered when you're below 81mph and the MAF sensor is registering below 40 g/sec. If you're flooring it, you'll be drawing much more than 40 g/sec through the MAF sensor...

Basically the P0420 fault is only being checked under relatively moderate conditions. The ECU is checking to see if the pre-cat O2 sensor is switching between rich and lean faster than the post-cat O2 sensor during closed loop fuel control. If it's not, that's an indication there's something wrong with the cat.
 

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Discussion Starter #3
According to the service manual, a P0420 fault (Catalyst System Efficiency Below Threshold) can only be triggered when you're below 81mph and the MAF sensor is registering below 40 g/sec. If you're flooring it, you'll be drawing much more than 40 g/sec through the MAF sensor...

Basically the P0420 fault is only being checked under relatively moderate conditions. The ECU is checking to see if the pre-cat O2 sensor is switching between rich and lean faster than the post-cat O2 sensor during closed loop fuel control. If it's not, that's an indication there's something wrong with the cat.
Ah! Great information!

Thanks!!! :up::up:
 
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