This just started yesterday. After letting the car warm up, due to cold weather, while driving with the heat running, I noticed that the Check Engine Light started flashing. Good thing that I was already at work. After work, the car had been sitting for hours, the light stopped flashing. How do I diagnose this problem and whatcould it be?

 

Probably not related to the heat being on but could be related to the engine temperature. A flashing CEL can only mean one thing. Severe cylinder missfire detected. Was the engine sluggish or running rough when the CEL was flashing? Need to get a code that will hopefully be a P0301-P0306 which would tell you which specific cylinder was missfiring instead of a P0300 random missfire.

 

The engine did not get sluggish or start running rough. I kept an eye on the Temp. Gauge and it never went above the normal level. With the P0301-P0306 codes, do the last number indicate which cylinder it is? If it is a random missfire, do I need to replace all the plugs? The last time that the car was tuned up was around Sept. '06.

 

Yes the last digit indicates the cylinder #. Sept 06 was not that long ago that you should need new spark plugs unless theywere champions or something. NGK or NDbest for Mazda. What engine do you have JEMac?? The 2.3 supercharged or regular 2.5 V6?

 

I have the 2.5 v6. Back in Sept. '06 I also had the EGR Valve replaced. Don't know if this is related to the CEL or not. The CEL only comes on if the Heat is on for a period of time. If I do not turn on the heat, the CEL does not blink. Don't know why. I wonder if it is some type of sensor for the heater core that may be indicating a problem there.

 

No sensors in the heater core or in the cooling/heater system that would cause the CEL to flash like that JEMac. Missfire code is being set but is not related to the heater being on. Check the code #.

 

I got 2 codes. One is P0300-Random Misfire and P0400 (I think) for EGR Malfunction. I recently had the EGR Valve replaced. I will try to replace all of the hoses before I replace that valve again. Any advice on the P0300 code? I do have the spark plugs that you recommended. A friend of mine said that it could be the Spark Plug wires, not OEM, that could be causing the problem.

 

Plug wires could be part of the problem as well as distributor cap and rotor. Random missfires are rather more difficult to diagnose as the code is not giving you a specific area to look at. The P0400 EGR flow malfunction code could be the cause of the random missfire too if the valve is sticking fully or mostly open at low rpms.When the CEL was flashing, did the engine idle appear to be rough. That could be indication of EGR sticking open as it is usually more evident at idle as opposed to higher rpm's. The EGR flow malfunction could also be due to loss of vacuum supply to the boost sensor solenoid and boost sensor due to a restricted or clogged port in the manifold. By this would mean that the EGR valve is working perfectly but the PCM is just not "seeing" it due to the clogged vacuum port.

 

I will try an replace the vaccum lines that are associated to the EGR Valve to see if that solves the problem. I have not clue as to where the boost sensor or the Boost Sensor solenoid are located. I will attempt to replace any hose that I see that have anything to do with the EGR Valve. I will also replace the plug wires, update the plugs, distributor cap and Rotor button with OEM Parts to see if that helps. I did not loose any type of power when the light started blinking. I was actually speeding down the highway at 90mph when it came on. I am at a learning curve. The only other Mazda that I own is a '97 626 that keep having the same problem with the EGR Valve code. That car has a bigger problem. It keeps running hot dispite changing the thermostat and water pump. While driving, it will shut down. If it sits for an hour, it starts right up.