a flashing engine light usually indicates a bad catalyst converter...the 0300 code is a multi cylinder missfire...you may want to tune it up before you try anything else..please print
CONDITIONS FOR SETTING THE DTC
ACTION TAKEN WHEN THE DTC SETS The PCM illuminates the Malfunction Indicator Lamp (MIL) under the following conditions:
CONDITIONS FOR CLEARING THE MIL/DTC IMPORTANT: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than the three ignition cycles. Review the Freeze Frame or Failure Records for the last failure conditions.
DIAGNOSTIC AIDS IMPORTANT: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
TEST DESCRIPTION The numbers below refer to the step numbers on the diagnostic table.
allot of alcohol in the fuel would cause the light to flash and you would get a lot less mpg's.....also,as i said before a bad catalyst would cause all the problems you just gave..
a muffler shop may be able to check the converter with a sniffer...another thing you may want to look at is the fuel pressure,,a weak fuel pump may also cause this,,these must have no less then 60psi at all times
Your answer was a little hard to interpret. So you had two occasions where this didn't work? My vehicle (6.0L) is having the 60-70MPH flashing check engine light with a P0300 with no noticable misfire or performance issues. Would it make more sense to relearn, or replace the sensor if that's the issue? I think the sensor cost is about $65, vs dealer time which would be more than that. When installing the new sensor do you need a Tech2 to sync anything or is it just plug and play?
Here is the service bulletin ...On this concern
Subject: 97-05 Vehicles with 4.8 5.3 5.7 and 6.0 Gen III V8 Engines and Misfires on One Bank - kw CEL diagnostics driveability DTC P0171 P0172 P0174 P0175 P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 #PIP3056 - (07/12/2004)Models: (00-05 Cadillac Escalade - C6 and K6) and (02-05 Chevrolet Avalanche - C1, C2 K1 and K2) and (99-05 Chevrolet Silverado - C1, C2 K1 and K2) and (00-05 Chevrolet Suburban - C1, C2, K1 and K2) and (00-05 Chevrolet Tahoe - C1 and K1) and (99-05 GMC Sierra C1, C2 K1 and K2) and (00-05 GMC Yukon - C1, C2, K1 and K2) and (03-05 Chevrolet Express G1, G2, G3, H1, H2 ) and (03-05 GMC Savana G1, G2, G3, H1, H2 ) and (04-05 Buick Rainier S1, T1 ) and (03-05 Chevrolet Trail Blazer EXT S1, T1 ) and (03-05 GMC Envoy XL XUV S1, T1 ) and (03-05 Hummer H2) and (04-05 Cadillac CTS-V DB) and (98-02 Chevrolet Camaro FB) and (97-04 Chevrolet Corvette YB) and (98-02 Pontiac Firebird FB) and (04-05 Pontiac GTO VB)The following diagnosis might be helpful if the vehicle exhibits the described symptoms.Condition/Concern: Check Engine Light with a P0300 due to 2 - 4 cylinders misfiring on the same bank of the engine. DTCs P0171, P0172, P0174 or P0175 may also set for the misfiring bank.Recommendation/Instructions: If the published misfire diagnostic does not isolate the cause, perform the following suggestions as necessary:
Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.NOTE: GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition.