P0300 Diagnostic Code - Random Misfire
Symptoms.
Engine may stumble or miss
Engine may be hard to start
you may notice no issues
Cause
Failing spark plugs or spark plug wires
Bad coil or coil pack
Failing oxygen sensor(s)
Bad fuel injector or more than one
Stuck exhaust valve
Bad catalytic converter
EGR valve or valve passage clogging
Bad camshaft position sensor
Bad PCM or ECM
The Fix
Best first action is a tune up, new plugs, wires, inspect all hoses and wire connections then reset the code. If it returns you will need to narrow it down to a system, coils and coil packs should be tested, catalytic converters for function ( do you smell rotten eggs?). A misfire that jumps cylinders could indicate a lean condition, do you have any other codes along with the 300? this will help clue you in to the source, check valve function to make sure they are opening and closing fully.
This is probably pone of the most difficult codes to troubleshoot, so start with the basics and work your way into the more expensive options, in many cases a good old tune up solves the problem, back it up with a fuel system cleaning and see where you stand.
under the hood by the engine
Reduced engine power is always accompanied by a trouble code. You must get the code diagnosed in order to establish your fix procedure. Get the code read at Autozone or someone that has a OBDII code reader.
You have to replace the cluster. Then the dealer must reprogram it with the appropriate mileage. You can find vendors on EBay. www.trailvoy.com Trailblazer enthusiasts forum
REMOVE ALTERNATOR FROM DRIVERS SIDE OF ENGINE BLOCK.
We have complete instructions at our enthusiasts forum at www.trailvoy.com very simple fix!
The P0300 is a multiple miss-fire code. The P1130 & P1135 are fuel air metering codes. Generally speaking you want to fix the first fault code in the list if you pull multiple codes at once. One code can cause other codes to appear. Fix the multiple miss-fire problem, clear the codes and see if the other two comeback.
Have a mechanic test the fuel sensor circuit. Likely the sensor has gone bad and will require replacement.
Start with replacing the thermostat.
replace cat
change your o2 sensor
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