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SES codes

Beamer

By Beamer
in Ask A GM Technician

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Beamer Enthusiast

Beamer

Posted
Posted

I had my codes read this morning and they came out as:

 

P0420

Catalyst Efficiency

Below Threshold

(Bank 1)

 

and

 

P0430

Catalyst Efficiency

Below Threshold

(Bank 2)

 

 

It sounds like a cat converter problem, but it does not seem to be clogged. I do have a slight leak at the flange gasket on the passenger side that I will replace later today. Will this cause a code like I am seeing?

 

Where are the O2 sensors all at? I see one just before the cat, are there some after, that would kick a code up like this?

 

 

Thanks for the help,

Mike

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted

I have never seen anything but a bad cat cause those codes. The system uses the O2's both before and after the cat to determine a cat's efficiency. No, a bad O2 would not cause those codes.

  • 2 weeks later...
Beamer Enthusiast

Beamer

Posted
  • Author
Posted

Thanks for your response. I have since posting the question and before realizing that you gave an answer, purchased 2 O2 sensors. I guess I may need to look into replacing the CAT assembly. I take it that is a little pricey. Any tips for someone that may find it difficult to slap a large cost in that easy?

 

Thanks again...

 

Mike

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted

Cats are not cheap. Probably $400 to $500 from GM. You can get aftermarket cats much cheaper, though I can't speak for their quality. We would never use anything but OE in our shop.

 

Keep in mind that cats have an 8/80 warranty, so if you have less than 80k on your truck, it's still covered.

Beamer Enthusiast

Beamer

Posted
  • Author
Posted

I just put a tune up on the truck at 117K miles, and I am thinking it was origonal, not sure. The motor definately ran a little rough. It definately runs better now, but my neighbor says it sounds a little off when I drive away.

 

I replaced the plugs with Delphi platinum for this motor, Accel 8.8mm wires, and a cap and rotor from Advance Autoparts along with a Purolater Air filter. This afternoon, I re-gapped the plugs to .060, vice the .045 that they came. And I checke compression and it seemed all good with these results:

 

1 185

2 190

3 182

4 187

5 185

6 185

7 190

8 192

 

This seemed very good to me. I then thought and tapped on the converters when it was running as I have read to check them that way, but did not hear anything different. Is there a definition of what I may hear if they are a problem in general?

 

Also, with the codes mentioned before, reading as the cats are bad, if they are, will that cause my motor to run bad? Or are they basically an after the cat monitor system? Basically, is the info used for the control system of the motor?

 

Thanks for any and all help that can be given...

 

Mike

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted

The cat(s) do not have to be broken and rattling or clogged to fail the efficiency test. They could simply be contaminated or just plain "worn out".

 

If the cats have just lost their efficiency, the vehicle will most likely not run any differently than before. It's only when they're clogged that they will affect driveability.

  • 7 months later...
Beamer Enthusiast

Beamer

Posted
  • Author
Posted

A few months later, I would like to re-vivit my problem.

 

I have a 99 Tahoe with the 5.7L

 

I replaced the cat pipes with a bolt in system from Summit (I know it is not GM, but that is all I could afford)

 

The SES light went out on its own. It has since came back, and I obtained the readout and it has the origonal...

 

P0420

Catalyst Efficiency

Below Threshold

(Bank 1)

 

and

 

P0430

Catalyst Efficiency

Below Threshold

(Bank 2)

 

 

 

 

AND NOW IT HAS:

 

 

PO442

EVAP Emission

Control System

Leak (Small)

 

 

 

 

Could this PO442 have caused my 420 and 430 to come back up?

And what is it sensing wrong, and possibly what could cause that?

 

I can feel a slight miss occasionally, and am sure it is not running up to par.

 

I very much appreciate any and all help given,

Michal

Norseman Senior Enthusiast

Norseman

Posted
Posted
A few months later, I would like to re-vivit my problem.

 

I have a 99 Tahoe with the 5.7L

 

I replaced the cat pipes with a bolt in system from Summit (I know it is not GM, but that is all I could afford)

 

The SES light went out on its own. It has since came back, and I obtained the readout and it has the origonal...

 

P0420

Catalyst Efficiency

Below Threshold

(Bank 1)

 

and

 

P0430

Catalyst Efficiency

Below Threshold

(Bank 2)

 

 

 

 

AND NOW IT HAS:

 

 

PO442

EVAP Emission

Control System

Leak (Small)

 

 

 

 

Could this PO442 have caused my 420 and 430 to come back up?

And what is it sensing wrong, and possibly what could cause that?

 

I can feel a slight miss occasionally, and am sure it is not running up to par.

 

I very much appreciate any and all help given,

Michal

 

The most common reason for that code is the gas cap is loose or not on correctly.

 

Check the gas cap first and see if the light turns off after a few days.

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