Just got a 1991 Blazer VIN Z with 4.3l

SES light come on on the way home, checked codes and got 42 & 43


Code 42:
"The EST signal did not change when the ECM applied bypass voltage to the ignition module."

Code 43:
"ECM did not detect a knock signal during near wide open throttle operation with coolant temperature above 194F or the knock signal was present for 5 seconds or more during normal engine operation"


So, in searching the board, 43 leads to replacing the Knock Sensor... any particular one, or both?

I couldnt find anything on the code 42 though.

The truck runs well enough, but then again I am used to driving 20+ year old POS cars...

I just want to take care of any potential problems while I have the money to do it.

let me know what you think.

 

DTC 42 is for the Ignition Control Module in the distrubutor. The easiest thing to do is pull the module from the distrubutir and take it to an auto parts store and have it tested. They all (to my knowledge) test them for free. I like to have them tested at least three times one after another. Others like to have them tested like ten times one after another. If it's good post again. There are more tests you can do. Just pretty late to post them tonight.
DTC 43 I wouldn't just replace them cause you have some extra coin. That's the way you don't have any extra when you need it. There are some checks you can do on the circuit. First just see if the connector fell off of one of them. Kinda low on the motor. Too late tonight to post troubleshooting.
If anyone else wants to jump in go for it.

 

Knock sensor - down behing the distributor I think, or on the passenger side between the oil pan and exhaust manifold... Its a real bugger to get a hand onto. Look for the connector to be broken off or unplugged, I wouldnt stick my hand in there if the motor is hot and you are going to get your knuckles bashed getting it out.

Ign Module - Unhook battery. Take off the distributor cap while leaving all the spark plug wires attached to it and twist out of the way. Pull the rotor straight up and off, dont worry about which way it points, it only goes back on one way. The module has the 2 wire plugs attached into it, unplug them and use a small torx screwdriver to undo the 2 screws that hold it on. Have the parts place test it a few times and a new one will be less than 40 bucks if it fails. You can also do what I do is just get the new one, and if it doesnt work, clean it up really good and return it to the youngest guy working there telling them you never needed it afterall.

Also check in here tomorow and Ill bet Gimpy can give you some troubleshooting pointers for it, hes my car repair guy now!

 

I'm retiring.
I had put the troubleshooting procedure here but when I went to post it, it disappeared. Sucks . Get back with you later.

 

DTC 43
Real quick caise I gotta split. The two knock sensors are located pretty far down on the engine adn of course in the back of both sides. They will have a single blue wire going to them.
1) Disconnect both sensors and check the voltage at the connectors. Should be 5 volts. If both are at 0 you either have an open or grounded circuit between the splice and the PCM (terminal B15) or a bad PCM.
2) If you have one at 5 v and the other at 0 v you have either a open or ground in the 0 v circuit betweenthe sensor connector and splice
3) If you have both connectors reading 5 v measure resistance between sensor terminal and ground. Should be 8200K ohms (believe this is a typo in the book - probably just 8200 ohms) Resistance range soec - if knock sensor measures lrss than 2100 ohms or open circuit replace sensor. @ scenarios here are possible. Within spec - 2100 - 8200 ohms?
A) If Yes you have either a faulty knock sensor connection or a faulty PCM
If No you either have a faulty knock sensor installation or a faulty knock sensor.
This is the way to troubleshoot problems. If you just want to throw parts at it you might fix it but if it's a wire problem all you did was waste your money. If you read enough of these posting you'll see where guys have thrown hundreds if not thousands of dollars at a problem by replacing parts and still have the same problem. I call this "shotgun troubleshooting" and pretty soon you won't have any of that "extra money" left that you have now. Besides it's kinda fun to see what was really wrong and fix it. You should get yourself a good service manual for your truck, one with a good troubleshooting procedure in it as well as it should tell you how the systems operatte. That's the first step in repairing a problem. The best are the factory manuals, second (IMO) are the Chilton books and if I need something to start a fire with the Haynes manual (just doesn't give you enough info or leaves you hanging). Good luck. These are really easy fixes. If you haven't worked on one of these you're really in for a treat.