2003 Tahoe flashing check engine light

[OR VietVet]

In all my years in shops, I never saw a flashing CEL. Lots of flash once or twice then off or on solid when came in shop.

 

[rockola1971]

In all my years in shops, I never saw a flashing CEL. Lots of flash once or twice then off or on solid when came in shop.

Ive seen it many times BUT it happened when engine was under a load (driving). Flashing CEL means there is active misfire happening on 1 or more cylinders. You may not even be able to hear it but those knock sensors sure hear it.
The last time I saw it was on my 03 Tahoe 5.3L FF last year when I had a bad spark plug wire. It fell apart at the spark plug boot just inside it.

 

[Scottydoggs]

OP's title for this thread included "CEL Flashing"...

GM Owner's manual mentions this on CEL:
"Light Flashing — A misfire condition has been
detected. A misfire increases vehicle emissions
and may damage the emission control system on
your vehicle. Diagnosis and service may be
required."

Anything rising to the level of making the CEL flash would have a code stored, even if it is only pending.

Before I got my Tech 2, I saw pending codes on my system with my Zurich scanner from Harbor Freight.
I didn't even have an active CEL on mine and was able to see a history of codes that were either old or still pending.
A lot were things like brake lamp and other issues that were repaired by the previous owner, but they didn't fully wipe the code history after the repairs were complete.
I found them under the GM OEM Enhanced sub-menu.

Anyway... I was just saying that there should be a history record of all stored and pending codes that the OP should be able to access to see what was going on.
I could be wrong, but I don't think pending codes just disappear when the engine is shut off. I am pretty sure the computer just sits on them until enough errors are collected to trip the CEL warning on the cluster.

if your using a cheap simple scanner the codes are gone. even my hptuners wont show me code history. but a pricey scanner will do all that and more. most of us dont have one of them real good scanners or tech 2's. most if at all have a 20 dollar actron.

im aware of the flashing cel op has. id put money on his cats are shot. like i said only two things really make the cel flash, cats are bad or you need a tune up like super bad.

 

[OR VietVet]

Ive seen it many times BUT it happened when engine was under a load (driving). Flashing CEL means there is active misfire happening on 1 or more cylinders. You may not even be able to hear it but those knock sensors sure hear it.
The last time I saw it was on my 03 Tahoe 5.3L FF last year when I had a bad spark plug wire. It fell apart at the spark plug boot just inside it.

You are likely still in shops and my shop times, after 35+ years, ended in 2010 and has been quite a while since I controlled rig flow in a shop and listened to customer complaints about their rigs.

 

[rockola1971]

You are likely still in shops and my shop times, after 35+ years, ended in 2010 and has been quite a while since I controlled rig flow in a shop and listened to customer complaints about their rigs.

Nope not me. Havent worked in a shop for many decades. I dont have the patience for customers anymore. They are not always right, they are usually dumber than a hammer.
Seen some of the type right here on this forum but I can keep it to myself and make fun of them just not out loud unless I call the wife in here to see what exactly is mixed in with mankind.
I dont mind helping people out here at all just like you and many others do here. What I do mind is when someone refuses to listen and then ends up chasing their own tail or makes things worse. I let them fail.

 

[OR VietVet]

Nope not me. Havent worked in a shop for many decades. I dont have the patience for customers anymore. They are not always right, they are usually dumber than a hammer.
Seen some of the type right here on this forum but I can keep it to myself and make fun of them just not out loud unless I call the wife in here to see what exactly is mixed in with mankind.
I dont mind helping people out here at all just like you and many others do here. What I do mind is when someone refuses to listen and then ends up chasing their own tail or makes things worse. I let them fail.

Could not have said it better about customers coming in to shops, loved talking to women because they did not pretend to know more about the rig than me, and I have been called out here by someone asking for help and I tell them that year, make, model, engine, trans, previous work, chronological order of events and decent info sharing would really help. Just like when I was running shops. I then tell the person asking for help, "cant help you if you want to find a safe room from my requests".

I really respect your advice and how straight forward you are with info. Keep it up.

 

[garren19714]

Probably his is non-Flex. FF trucks this year have a fuel filter.

@garren19714 are you sure it's a 4.6L?

Hard to believe that a flashing CEL would not have a current or history code.

Scanned again and no codes

 

[rockola1971]

Scanned again and no codes

Did you check for pending codes or historical codes? Does your scanner have those options?

 

[MassHoe04]

Did you check for pending codes or historical codes? Does your scanner have those options?

I agree with @rockola1971. Whatever the computer thinks is important enough to trip the CEL light and make it flash has to have some reason in the memory banks somewhere...

It could possibly be some weird grounding issue. But, even if they were false codes or a bunch of pending only codes, the computer would be hanging onto that information.

Owner's manual specifically calls out a flashing CEL as indication of a "serious misfire". If it were me, I would tend to focus my attention on fuel and ignition before pulling cats apart.

Heck... Go for the easy stuff first! Get your hands on (buy/borrow/find a friend) a Tech 2 or other bi-directional scan tool. See if any buried code activity points to a simple problem with more accuracy than guessing. You will save a lot of time and money.

$300 for a Tech 2 clone. A good bi-directional scan tool (like an Autel tablet or similar) can run $600-$900 for a really good one without going overboard. Tech 2 will likely pay for itself with one or two repair diagnoses. A tablet will also pay for itself, but might take a little longer.

Good luck!