My check engine light is coming on and I pulled the codes and they are: 12 and 43
I have a 1992, does anyone know exactly what these codes are, and how do you figure out the fix for them. I understand that the computer might read a problem but that might be the result of something else before it shows a code from another sensor?

One thing I can add is there is a whinning coming from the engine when you first start the car - like a high pitch squeal. I did purchase a stethoscope and tried listening for it but the squeal stopped before I could find it. I thought it might be the alternator.

I also drove the car the other day and if I remember correctly the volts should read 14.2 or close too, but when I stopped at a light the volts dropped to 12.4 or so. Is this common or should it always read in the 14's even when stopped at a light?

Two summers ago I did replace the water pump and the opti spark. The new opti spark is an MSD vented one.

Need help please
Thanks Chris

 

ttt

 

I don't know what the codes are, but just a guess, could the belt be loose or worn?

 

Code 12 is actually the start of all codes stored in the ECM; you should have see another Code 12 at the end of the codes.

Code 43 points to a bad knock sensor or the ECM is seeing a voltage of above 3.62v or below 1.44v when CKT496 (the dark blue wire going to the knock sensor). This voltage range typically indicates an open circuit or shorted to ground.

If the sensor is bad, the ECM will test for engine detonation (knock) under load. The coolant temp has to be 203 degrees or higher and the engine load is based on air flow. You can reset the codes by disconnecting the battery for 30 seconds. Then try some hard acceleration after the coolant temps reach 203 or more. If the CEL comes on at that point and another Code 43 is seen, then it's most likely a bad knock sensor.

A GM Tech-1 scan tool is going to be the best way to check the sensor. It's also possible the MEM-CAL chip is not seated properly in the ECM.

As far as the voltage readings, anything in the low 14v range is fine, especially after start-up. But 12.4 may indicate a bad battery or alternator. Check the alternator output at the stud where the heavy red wire is connected when you hear the noise. I'll bet you have a bad alternator.

 

Code 43 points to a bad knock sensor or the ECM is seeing a voltage of above 3.62v or below 1.44v when CKT496 (the dark blue wire going to the knock sensor). This voltage range typically indicates an open circuit or shorted to ground

Inspect the knock sensor connectors first for grease, grime, oil, etc. Sometimes build-up on them will cause them to throw a trouble code. Remove the connector, then spray with electrical contact cleaner and allow to air-dry before reconnecting. The fix could be as simple as that.

 

Thanks for the imput. I'll try those tips and see what I come up with!

Thanks again for your help!

Chris

 

And the squeal you hear soon after startup may just be your AIR pump. They are LOUD suckers.

Another place to check is the cooling fans - you may have a bearing starting to go on one of them.

My alternator did not make any bad noises before it decided to go out. Volts on the display just started to drop

 

And the squeal you hear soon after startup may just be your AIR pump. They are LOUD suckers.

Indeed. Ever hear the ones on the LT-5's? They sound like WWII air raid sirens!