Help- Check Engine Light Flashing Randomly!

MKWL · September 7, 2009

Well, for the last month or so, my check engine light has been randomly (anywhere from 3 to 35 flashes at a "time") flashing when driving at highway speeds (only at 60+ MPH), and at 50MPH when towing a heavy load (5K+).

I took the truck to advance auto today to get it scanned- it pulled a P0300 code- random/multiple cylinder misfire.

The truck runs 100% (near as I can tell) fine, runs around town no problem (no light so far), and on the highway fine, just the light is flashing at times.

It idles smooth- same as it always has...

Any ideas on the culprit? The truck has 72,000 miles on it, maintained well, original plugs/wires etc.

Thoughts?

txab · September 8, 2009

Here's some info:

http://www.random-misfire.com/

MKWL · September 8, 2009

Okay, thanks.

Does anyone know what the GM emissions warranty covers- and for how long? I bought my truck used in '07 with 40,000 on it, now has 72,000 on it- anyone?

Back to the misfire- anyone think it could be that the truck needs to "re-learn" the crank position sensor? Symptoms?

The thing that puzzles me is that my truck only does it at highway speeds, and it's very random???

hockeypro1411 · September 8, 2009

That makes two of us. I'm tempted to do the electrical tape mod.

txab · September 8, 2009

That makes two of us. I'm tempted to do the electrical tape mod.

You still haven't been able to figure out what is causing your problem? What's the tape mod involve?

MKWL · September 8, 2009

Well, my truck's at the dealer- hopefully they'll have a diagnosis for me by tomorrow- we shall see...

hockeypro1411 · September 9, 2009

That makes two of us. I'm tempted to do the electrical tape mod.

You still haven't been able to figure out what is causing your problem? What's the tape mod involve?

No I still have no idea what's causing it. This thread describes it better than mine did.

Lol you've never heard of the electrical tape mod? You cut a square of electrical tape and stick it over the check engine light. This way you'll never know if it's on.

txab · September 9, 2009

That makes two of us. I'm tempted to do the electrical tape mod.

You still haven't been able to figure out what is causing your problem? What's the tape mod involve?

No I still have no idea what's causing it. This thread describes it better than mine did.

Lol you've never heard of the electrical tape mod? You cut a square of electrical tape and stick it over the check engine light. This way you'll never know if it's on.

Yeah I've heard of that one. Just a little slow on the uptake today.

MKWL · September 9, 2009

I've been reading, found that other guys with the same symptoms had a bad ECM ground- anyone think this might be it? It's at the dealer right now, so I'm waiting to hear back later from them on what they think the problem is...$$$$$.

hockeypro1411 · September 10, 2009

I've been reading, found that other guys with the same symptoms had a bad ECM ground- anyone think this might be it? It's at the dealer right now, so I'm waiting to hear back later from them on what they think the problem is...$$$.

I can't wait to hear what they say. Mine just tells me that it needs new plugs n wires. Apparently me telling him that I replaced them a week ago wasn't doin' it for him.

MKWL · September 10, 2009

Well, GM called me up yesterday- they said that they pulled the code P0300 (duh- I pulled the same thing), and the only way to correct teh problem was to start replacing parts hoping to get it fixed, costing me an indefinite amount of money and time. So, I took the truck out of their hands, and will run it as is until I can get it home in a month or so to have a buddy of mine look at it. The weird thing is, it only comes on with teh RPM's higher than 2K or so, and I can stomp on it and it still runs fine???? I'm at a loss...

Hockeypro- how many miles have you put on yours with the light flashing?

txab · September 10, 2009

I thought I posted yesterday about some info I found concerning aftermarket alarms. Maybe I didn't.

Anyway, found it so I thought I'd throw it out there for those it might affect.

Info - Misfire DTCs P0300, P1380, P1381 and Catalytic Converter Damage Due to Installation of Alarm Systems #02-06-05-004A - (Jan 9, 2004)

2004 and Prior GM Passenger Cars and Light Duty Trucks

2003-2004 HUMMER H2

2004 and Prior Isuzu Light Duty Trucks

This bulletin is being revised to add the 2004 model year and include specific DTCs in the title line. Please discard Corporate Bulletin Number 02-06-05-004 (Section 06 - Engine/Propulsion System).

General Motors Engineering, in an effort to determine the root cause of catalytic converter damage, has determined that aftermarket alarm systems incorrectly installed in vehicles have the potential to cause misfire codes and damage to the converter. These alarm systems use a circuit interrupt which utilizes the ignition circuit on the vehicles.

These alarm systems utilize mechanical relays and normal vehicle movement can trigger these relays to engage and disengage the ignition circuit while the vehicle is in motion. These disruptions of the ignition circuit, which occur in milliseconds, may cause more fuel to be commanded. Over time, this dumping of fuel on and off again can cause misfire codes and ultimately damage the converter assembly.

Important

Engineering could not identify any alarms that utilize solid state circuitry that would eliminate this concern. Because of this, it has been determined that all alarm systems must be routed through the starter circuit in order to avoid this condition.

Dealers must be aware of this issue and take note of the wiring on vehicles with alarm systems that come in for repair, particularly for catalytic converter damage that seem to have no known root cause.

hockeypro1411 · September 12, 2009

Well, GM called me up yesterday- they said that they pulled the code P0300 (duh- I pulled the same thing), and the only way to correct teh problem was to start replacing parts hoping to get it fixed, costing me an indefinite amount of money and time. So, I took the truck out of their hands, and will run it as is until I can get it home in a month or so to have a buddy of mine look at it. The weird thing is, it only comes on with teh RPM's higher than 2K or so, and I can stomp on it and it still runs fine???? I'm at a loss...

Hockeypro- how many miles have you put on yours with the light flashing?

Probably around 5,000. I can't feel a misfire when it flashes. From what you describe, we've both got an identical problem.

brims · September 12, 2009

Well, GM called me up yesterday- they said that they pulled the code P0300 (duh- I pulled the same thing), and the only way to correct teh problem was to start replacing parts hoping to get it fixed, costing me an indefinite amount of money and time. So, I took the truck out of their hands, and will run it as is until I can get it home in a month or so to have a buddy of mine look at it. The weird thing is, it only comes on with teh RPM's higher than 2K or so, and I can stomp on it and it still runs fine???? I'm at a loss...

Hockeypro- how many miles have you put on yours with the light flashing?

Tell them to do that, but you're not paying for anything that doesn't directly fix it. I know it won't work, but hey. That's crap for them to just throw your money at it. They are the technicians they should be able to know what the most likely cause is and test for that.