tgates

12 is No reference pulses to Electronic Control Module (ECM).
-How do i solve this problem?

43 is Low voltage at electronic spark timing circuit.
-How do i solve this problem?

Injuneer

"12" indicates the PCM has entered diagnostic mode - its a "handshake". It always flashes "12" three times when you short the ALDL pins to starts the sequence.

DTC 43 is for a faulty knock sensor circuit, at least on the TPI engines. Pull the harness connector off the knock sensor. Key on/engine off, measure the voltage from the single wire in the connector to the block. Should be 5V. With the wire still off the sensor, measure the resistance between the single pin on the sensor, and the block. Should be in the range of 3,300-4,500ohm. Put the harness connector back on the knock sensor. Measure voltage from the single pin the the block. Should be in the range of 1.5 - 3.5V.

tgates

every code chart that i look at says that code 43 for 1991 camaro 5.7 tpi "Low voltage at electronic spark timing circuit."
-anyone know what to do to fix this???

Injuneer

OK... and I'm working off the Howell Engine Development manual, which includes copies of the GM factory diagnostic charts and logic diagrams. Code 43 = Electronic Spark Control (ESC) Circuit - 1990 - 1996 TPI and LT1.

Your charts showed 12 as a valid fault code. It isn't. Think about it.

But since you apparently you feel you have all the answers you need, I'll butt out and let someone else take this one.

RedIrocZ-28

I got this: The ECM did not detect a knock signal during near wide open throttle operation with coolant temperature above 194� F or the knock signal was present for 5 seconds or more during normal engine operation.
Electronic Spark Control (ESC) Circuit .

http://www.troublecodes.net/GM/

Kevin91Z

Code 12 is normal. It just means the engine is not running.

Code 43 is the fault in the knock sensor. Either its unplugged, or there's a short in its wire. Perhaps the wire melted against your headers?