Hello Mazda Forum,

I am looking at a Mazda 6 2005 - 6 Cyl with ~ 100k mi. The current owner says that these codes are up and wants to dump the car cheap:
P300 - Random Misfires.
P2189 - System too lean @ idle Banks 2. A bunch of other System too lean. (2177 and 2179)
P2197 - O2 Sensor Stuck Lean - Bank 2.

A week before these problems started, an oil change and transmission fluid change were done.
So what I want to know, is how to differentiate between a vacuum leak, O2 sensor problem, or timing chain issues causing the random misfires? I haven't ruled out a MAF problem.

I know to look at my scanner data and look for the O2 sensor controlling or being active, in which case, it is working. I know to look at trims if the sensor is working to identify vacuum leaks but the P300 code bugs me. It is exactly what you get if the timing chain tensioner is malfunctioning and the timing chain has jumped a tooth or two. So how do I diagnose that? How do I rule that in or out.

This will be done as part of a pre-sale inspection. Any ideas?

 

You have to many things going on for to long.
I would first note your DTC then do a simple basic clear codes.
next do a compression test
follow up with a leak down test if the reading are low from the compression test or if comparing the highest to lowest cylinders more then 20%

After the compression test note all the finding then start the engine. If drivable drive until the engine check light returns and get the DTC quickly. If your scanner has the capability look at permanent DTC and your I/m monitors. Not everything you find.

this will give you a better starting point then where you started and posted .

 

Welcome to the forum

 

P0300 is an anomalous DTC when the controlled variable are out of the ECU programming range. Basically many things or a combination of things can generate that DTC. At this point it is less concerning and more or less should be noted but to worried about at this stage from you information thus far.

 

Hey Callisto,

Thanks for the input. It is useful to know that the P0300 code can be triggered by out of range sensors. I don't think I have all the codes, so I am going to get better information and watch the MAF/O2 sensors through operation and warmup. If I don't see a clear problem, I don't think I will buy the car. I have learned from these forums that the Purge Solenoid Valve can have problems (P0443) and the snorkel will crack.

Have a great day.

 

If you get an vehcle prior to 2020 look into getting an Ultra Gauge