02 Silverado 5.3L blinking Service engine light

[Trav]

Originally Posted By: bdcardinal
Originally Posted By: Trav
Naw just throw money and parts at it. The euphoria of placing the online parts order and visions of having the vehicle repaired like new again will carry you over for a few days but after hours of fruitless hard labor and failure the let down is merciless. The old emotional roller coaster rides again.

I love when customers come in and say they have a check engine line on and what should they get. I usually ask "did you run the code or have a mechanic look at it?" and the usual response is "no they wanted to charge me." Those are the big money tickets where no parts are returnable. I usually recommend they go to service as it will be cheaper than a shotgun diag or throwing parts at it until something sticks.


It never fails, many people complain about paying to diagnose the problem and rather throw parts at it until they are almost bankrupt. I see it all the time, guy goes to AA, AZ etc and they diagnose an issue as a bad O2, the next thing you know the guy has 2 wide bands and 2 O2 sensors in the hand, puts them in and nothing different, now he comes your way.

The cheapskate then ask you to check it, you do and find out its just a bad purge valve then he calls you a crook for charging him $75 to scan it because AA did it for free.
You tell them the scan tool cost a lot of money and needs to earn its keep, their response is its not their problem how you pay for your tools.

 

[demarpaint]

Originally Posted By: Trav
Originally Posted By: bdcardinal
Originally Posted By: Trav
Naw just throw money and parts at it. The euphoria of placing the online parts order and visions of having the vehicle repaired like new again will carry you over for a few days but after hours of fruitless hard labor and failure the let down is merciless. The old emotional roller coaster rides again.

I love when customers come in and say they have a check engine line on and what should they get. I usually ask "did you run the code or have a mechanic look at it?" and the usual response is "no they wanted to charge me." Those are the big money tickets where no parts are returnable. I usually recommend they go to service as it will be cheaper than a shotgun diag or throwing parts at it until something sticks.


It never fails, many people complain about paying to diagnose the problem and rather throw parts at it until they are almost bankrupt. I see it all the time, guy goes to AA, AZ etc and they diagnose an issue as a bad O2, the next thing you know the guy has 2 wide bands and 2 O2 sensors in the hand, puts them in and nothing different, now he comes your way.

The cheapskate then ask you to check it, you do and find out its just a bad purge valve then he calls you a crook for charging him $75 to scan it because AA did it for free.
You tell them the scan tool cost a lot of money and needs to earn its keep, their response is its not their problem how you pay for your tools.



Great point, plugging in a scan tool and reading a code is one thing. Using the data, and applying knowledge from years of experience and making a proper diagnosis is another story. The problem today is we're living in the point and click generation. People actual capable of making a diagnosis are far and few, but well worth it if you can find them. Tossing parts at a problem is easy, and common. The parts stores love it too.

 

[bdcardinal]

Originally Posted By: demarpaint
Great point, plugging in a scan tool and reading a code is one thing. Using the data, and applying knowledge from years of experience and making a proper diagnosis is another story. The problem today is we're living in the point and click generation. People actual capable of making a diagnosis are far and few, but well worth it if you can find them. Tossing parts at a problem is easy, and common. The parts stores love it too.


Yup especially when they try to bring back parts that were obviously installed and we tell them they are not returnable. They try to hide it by cleaning them off, but the witness marks from bolts on the plastic and the electrical spades are obvious. Especially when it is a part that I mark on the little bushing with threads and the markings are wiped off.

 

[SteveSRT8]

Diagnosis has always been the "meat" of the repair professional. No reason you shouldn't pay for expertise.

In the old daze I moonlighted at a small indie shop. We had two "parts changers" that would simply perform the necessary parts swaps as diagnosed by the owner. They knew little about cars...

 

[Gito]

Replaced the spark plugs yesterday.

I got the following codes:
P0300 Multiple Cylinder Misfire
P0420 Catalyst System Low Efficiency (Bank 1)

 

[Trav]

It sounds like a cat may be toast and blocked, common enough. Remove the front O2 sensors, tie them up with a zip tie out of the way, clear the code and run the engine, if the P300 doesn't come back in a few min of running you probably have a plugged cat. Its going to be loud.
Pull the pipe off the rear of the cat and look through it with a flash light, you will see if its blocked or not (its probably melted) depending on what you find there are a few options. Post back.

 

[Gito]

Originally Posted By: Trav
It sounds like a cat may be toast and blocked, common enough. Remove the front O2 sensors, tie them up with a zip tie out of the way, clear the code and run the engine, if the P300 doesn't come back in a few min of running you probably have a plugged cat. Its going to be loud.
Pull the pipe off the rear of the cat and look through it with a flash light, you will see if its blocked or not (its probably melted) depending on what you find there are a few options. Post back.



Just to be on the same page.
Bank 1 is drivers side, and thats the pipe that I'm pulling off, right? Or do I check both CATS?

 

[Gito]

By the way, the truck is driving good since I replaced the plugs.
No roughness or idle issues.

I want to get to the bottom of all this and replace whats needs to be replaced.

Any advice is greatly appreciated

 

[Trav]

Did you reset the codes after performing the repair? Bank 1 is drivers side. Do you have access to a scan tool to get the fuel trims? If it6s running okay the cat probably isn't plugged badly if at all.
P300 is random misfire not bank specific.

Check this out.

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

 

[DP78]

This is a cat converter. It will cause a miss on that bank as the converter clogs. If you had access to misfire Data you would likely see it's the back cylinders, closest to cat, moreso than the front. I've been working on Chevys and Caddys for 16 years, I've seen it before. You will want to be sure you've don't have an issue causing a failure. Leaking injector or such. Although at the mileage you have it's likely more age than anything. These converters are separate, unlike later models that have them both in one Y pipe. You can get one converter provided it's available.

 

[Subdued]

PO420 is a bad cat converter. I mean, it *can* be a bad upstream O2 sensor, but it's usually a bad converter.

The readings between the upstream and downstream O2 sensors are too close, meaning the cat isn't doing its job.

You can cheat it by putting a defouler between the downstream O2 sensor and the pipe, but that certainly won't address why the cat failed in the first place (probably driving with the misfires)

 

[Trav]

There is little doubt the cat is probably bad but that's not the point at this stage of diagnosing the problem. You need to know if the cat is the cause of the misfires or fell victim to them.
If the cat is not plugged and not creating back pressure chances are good it is a victim of misfiring and not the cause of it, replacing it without addressing the root cause will just damage the new one.

A P420/430 inefficiency code will not cause misfires it simply means the cat isn't performing as it should and is inefficient for some reason, it can still be partially plugged and that's why you need to test it. Ideally you need to scan for fuel trims and misfire count on all cylinders.

Don't just throw a cat at and hope for the best, it may or may not fix it, proper diagnosing and keeping the cart behind the horse is everything, address the problem if there is one other than the cat first then put the cat in.

 

[GMBoy]

^^^^^ Trav is right on the money as usual. Add to this, if the cat is not plugged up. I would just install an anti-fouler (18mm size) to eliminate the 420/430 code and that will buy you plenty of time.

 

[Gito]

I replaced the intake manifold a year ago.

The service engine light at the time went away by itself.
Later I found out that the service engine lights need to be cleared completely from the computer by using the appropriate scan tool because even though the light goes away the code stays behind and can cause problems.

Well I procrastinated and the light eventually came back on.

It might have been that my CAT was already compromised prior to replacing the intake manifold. I don't know.

I'm not sure if replacing the intake manifold corrected the problem which resulted in a BAD CAT or if the BAD CAT is a result of other underlying engine troubles.

Drove the truck to the stealership today and hope that their computers will pick up any underlying issues.

I will update when I get the truck back

 

[Gito]

Got a call from the dealer this evening.

They told me it's a Bad CAT.
Hope that there's more detail on why the CAT went bad.

Not sure if they can show me data or explain more on why it went bad.

I will ask to speak to the Technician that worked on it and hope to get answers

 

[Trav]

He will just use a scan tool on it and check the fuel trims and engine sensor data, no big deal.

 

[Gito]

If there was anything odd, would they be able to notice it and blame that for causing the Cat to go bad?

I did tell the Service manager that I replaced the intake manifold one year ago and he wrote the note down on his paper

 

[Trav]

For sure. The two main culprits for early cat failure are heat and poisoning, any engine condition that causes excess fuel to be delivered by the injectors will raise cat temperatures so normal fuel trim values are a good indicator that the cats temp will remain in the normal operating range.

Things like vacuum leaks, injector clogging, false maf, map, tps, knock sensor and engine temp readings will prompt the ecm to alter timing, fuel injector pulse rates and pulse duration with the effects being measured by the front O2 (air/fuel monitor aka wide bad O2) the fuel trim readings will show this.
The cause of any abnormal trim readings can be diagnosed with the scan tool. A scan tool that can do some basic functions with a few bidirectional commands is a very valuable tool for the DIY mechanic, along with a vacuum gauge you can diagnose most things and save a fortune. I will be testing one 1 just got that is priced right for the DIY.

 

[Vikas]

The question is NOT that the converter is bad but the question is HOW bad? The code trips when the efficiency drops below 90%, so that alone does not tell you much. One really should put a tail pipe probe to check the actual emission before condemning the converter.

 

[Trav]

If its bad enough to cause a P300 it doesn't really matter whats coming out the pipe, its toast.