1999 Blazer 4wd 165,000 miles
I do not know the history of this vehicle, but I doubt if it has had much maintenence.

Codes
P0300 random misfire
P0420 catalyst effiency low
P0751 shift solenoid valve performance
P0753 shift solenoid A valve performance

I will attack the P0300 with a tune up, new fuel filter, new plugs, & check plug wires, cap & rotor.

P0420 I believe the PO300 may have been there for some time so I expect the misfire to have caused the P0420. Is it likely that the catalytic converter is shot or is it possibe that it might be ok after the misfire is fixed? If the converter is bad is there any downside other than excess emissions and throwing the P0420 again if the converter is not replaced?

P0751 & P0753 The driver says it takes longer than normal to shift up through the gears. However I'm not confident she knows exactly what it is doing.
I will check the electrical connector at the transmission first. Which solenoids are these codes referring to? Where are they located? I assume they are inside the pan. Are they easy to change? Any trouble shooting advice before changing the solenoids?

 

I had the last 2 codes you listed last week, researched it and everything I read said to change the ignition module in the steering column, so I went to the junkyard, found 1, pulled it, replaced mine and problem solved for a mere $8 a new 1 is $100 and I wasn't sure if it was going to fix the issue so I figured take the cheap way out to elimate possibilities. Well, 1st elimitation and my issues were gone! Could be something different with yours but its a place to start! Hope this helps!

 

P0300

P0420

P0751

P0753

Have you taken a read through any of the above threads?

 

Thanks 06. Did what you found give any reason why the ignition module would cause the solenoid codes to set?

 

This is due to a drop of voltage in one of the ignition sources from the ignition switch. The wiring schematics are linked to in my sig.

 

Thanks Sisk. I did do a search and found all of those except the 751. I'm not clear if they are for the same solenoid or 2 different solenoids.

I expect a tune up will clear up the 300 code. I was just wondering if the catalytic converter might be ok or if it is likely to be ruined.

Thanks Kyle. Is there a way to diagnose this before replacing the part? 06 said module. Is there a module also or are we just talking about the switch?

 

Have a look at the Tech Article (DIY) Index link in my sig. Look for the Ignition Switch replacement how-to's. There are two, the book method and then one that Jason (Wolfpack) wrote up.

As far as testing it, I suppose you could tap off of the power wire running down to the transmission and monitor the voltage.

 

No problem Terry. I wasn't sure if you knew the DTC board was there. A lot of times people post up about codes and don't realize they're all explained in great detail on the DTC board.

 

I really appreciate your pointing those out. I do search before posting but don't always find everything. This board is great about pointing out previous posts etc. to people. I will probably work on it Monday and see how things go.