Check Engine light blinking

Daryl LBZ · January 8, 2016

Thank you for the help though

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No problem. Just throwing out ideas.

saxplayer07 · January 8, 2016

No problem. Just throwing out ideas.

I appreciate all the help I can get

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Daryl LBZ · February 8, 2016

So did you ever figure out what the issue was?

saxplayer07 · February 9, 2016

So did you ever figure out what the issue was?

Random misfire (however not yet proven) and evap system leak. But the light still blinks around 70-80mph.

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Daryl LBZ · February 9, 2016

I'm stumped on this one. Sounds like you'd basically have to just throw parts at it which isn't very fun for the wallet.

Cosmic Charlie · February 9, 2016

My 2004 did it on the highway ONLY - was bad ground

google silverado grounds ....

http://www.2carpros.com/questions/chevrolet-silverado-2002-chevy-silverado-service-engine-soon-light-on-p0300

Daryl LBZ · February 10, 2016

My 2004 did it on the highway ONLY - was bad ground

google silverado grounds ....

http://www.2carpros.com/questions/chevrolet-silverado-2002-chevy-silverado-service-engine-soon-light-on-p0300

That's where mine has done it too, the only two times it's happened. Since I replaced the ground wire that goes from the battery to the engine block and frame it hasn't happened again.

intheburbs · February 10, 2016

It has to be something loose. The fact that it only happens at highway speeds, when the airflow through the engine bay is at its highest, is the key. What else could be the cause? Something is loose, and at higher speeds, it flaps in the wind and causes a misfire.

Daryl LBZ · February 10, 2016

That's a possibility. I know on the ground I replaced the smaller one was corroded pretty good, and so was the frame where it was bolted to. The best thing to do is probably just go over all the grounds first, and see if that fixes anything.

Kevinreitan · February 15, 2016

Just curious if you ever found anything. i get a flashing CEL but only uphill at HWY speed. its not storing a code.

2003 silverado 4.3

Cosmic Charlie · February 15, 2016

My Guess - at highway speeds the very high energy ignition does NOT ground good enough with the higher rpms --

my flashing CEL went away with the replacement of the ground under the drivers side door jamb / rocker panel area on the frame

silveradosid · February 16, 2016

my 2001 chev with the 5.3 did this. took it to dealer, multiple misfire codes. they replaced plugs and wires, cleaned the throttle plate. got truck back and first time on the highway it did it again. I was poed. it turned out that the cats were almost plugged, new cats and truck ran like new.

saxplayer07 · March 1, 2016

My Guess - at highway speeds the very high energy ignition does NOT ground good enough with the higher rpms --

my flashing CEL went away with the replacement of the ground under the drivers side door jamb / rocker panel area on the frame

Well I checked both grounds under the driver side of the cab and under the battery and both are in good condition.