My car was working fine last week. About 4 days ago, it started stalling and running rough, and my Check Engine Light came on. It was a P300 code. I took it to Pep Boys, and they said it was the spark plugs and spark plug coil, so I had them replace it. Ended up paying about $450 for all of that (including the diagnostic). Got my car back yesterday and it was running good and the CEL was off, so i thought the problem was solved. Now today the CEL popped on again, took it to Autozone and it's showing 420 (catalytic converter)....
Does this mean that Pep Boys did NOT need to replace the spark plug coil? Are these related? Why would my car be fine 5 days ago, and suddenly nothing is working? I can't afford to replace the catalytic converter when I just yesterday dropped $450 on the plugs and coil.

 

Probably not needed. Inexperienced mechanics just read the description and go with it. I am currently working on a p0420 that I am hoping to find is the #2 O2 sensor, but is probably the cat.

If there was ONLY a p0300 code, then they totally blew the diagnostic. There should have been at least one other code like p0301-p0304 which would pinpoint the particular cylinder. Since you now have the p0420 my guess would be a bad injector or 2. But, further diagnostics was and is called for.

If this is a 2006 HHR a new cat only runs around $120 (on EBay) and is probably a 1 hour or less job + gaskets. 2008 onward run $180, or so.

 

X2

Head on back to Manny, Moe, and Jack.

Give them a chance to make things right, or get your money back and head elsewhere for more diagnostics.

 

If your car was running rough before they replaced the plugs and a coil and now it runs well it probity needed the parts that they installed. The p0300 is a random cylinder misfire. The p0420 is catalyst efficiency below threshold. A misfire can shorten the life of the cat. Also a weak 02 sensor can set the code. I agree that you should take it back and have them recheck there diagnostic. Good luck

 

$450 for plugs and coils....wtf...I would attempt it blind before I paid that...what a rip off some of these places are, and they might not have fixed the problem? F that

just my opinion...not trying to get sidetracked

 

Not necessarily at all - the problem is back, or a variant of it. The first codes can have many causes. If the codes were cleared at the onset, without replacing anything, the problem would have been cleared until the hard error occurred again, or when the parameters were hit ad determined by the drive cycles.

 

I checked Ebay for coils for 2006, they run less than $200. The Boys seem to have Pep'd $200 in labor to remove the air filter housing.

 

May be the cost of those iridium plugs. You know how those precious metals costs have skyrocketed.

 

I was including $50 for the plugs.