It depends on what year you have. Some are in the back of the head and others are in the block where the block coolant drains are located. Some have one knock sensor and others have two.
code 43 is related to the spark control system. (esc) the problem is usually the knock sensor wiring connector is defective and/or the sensor. the sensor is located in the right /passenger side of the engine block near the starter.
Electronic spark control is not receiving sinal from knock sensor Try replacing knock sensor
code 43 except2.2or2.5 4flashes pause 3flashes electronic sparkcontrol knock sensor circuit probable cause faulty knock sensor or mem_cal.
knock sensor
knock sensor
I have a 1990 Pontiac Safari wagon that would not start,after much testing we found one bad fuel injector replaced it and car started but ran terrible, did more testing and found bad ignition module, replaced module runs better but now have code #43 knock sensor and engine is running in default mode switched ECM no help must be knock sensor don't think knock sensor would keep car from starting but the other things mentioned here would. Hope this helps. This wagon has 3.1 engine. Havent changed knock sensor yet.
On your 1988 Celebrity code 12 means the computer is working properly. You should always get a code 12 whenever you check for codes. Code 43 has to do with the Electronic Spark Control, specifically the knock sensor. It doesn't necessarily mean the knock sensor has failed, it could be in the wiring To check the knock sensor measure it resistance. It should read between 3300 and 4500 ohms. If it does not it may mean the knock sensor has failed. One of our cars recently posted a code 43. When we checked it out it turned out the terminal had come off of the knock sensor. When it was put back on it cleared up the problem.
Code 43 indicates a fault in the ESC (electronic spark control) system. It usually means the knock sensor has failed, or the wiring to the knock sensor is faulty. When this fails it causes the computer to retard the spark timing to protect the engine, resulting in stalling, poor performance and reduced mileage.
ESC / Electronic Spark Controll Circuit. and the knock sensor signal.
To attempt to answer your question I looked up the code 43 in my Factory Service Manual. The full answer and diagnostic procedure is much too long and involved to try to post in this format. If you don't have a manual you might be able to use one at a local library. But to give you some level of answer: Code 43 has to do with the knock sensor to ECM circuit. ECS should be ESC which is electronic spark control. The book suggests that the problem could be in the knock sensor, the ECM, or the wiring and connections between the two. Since you have replaced the ECM it would seem that the wiring and knock sensor remain POSSIBLE problems. Look particularly at the connector to the knock sensor. Corrosion or oil contamination in the joint is a possible problem. If not then the knock sensor would be the next check. The book says to connect an ohm meter between the terminal on the knock sensor and ground on the engine block. The resistance should be between 3300 and 4500 ohms. If it is not between those numbers then the book says to replace the knock sensor. The knock sensor screws (pipe thread) into the side of the block nearest the firewall, and goes to water coolant passages. If you take it out it could lead to coolant loss so have a suitable container ready to catch it. It is not in a convenient place to get to. Another thought: The knock sensor grounds on the pipe threads. Corrosion or contamination there could also be a problem. If you take the knock sensor out or replace it don't use thread sealant as it could interfere with the ground.
check the knock sensor if that's not it try the electronic spark control moduel
Code 43 is a knock sensor (ESC system fault). If you have a hard 'check engine' light, try this. Disconnect the negative terminal on the battery for a couple of minutes, then reconnect. Start vehicle. If the 'check engine' light comes on within 15-20 seconds or so, chances are either the connection to the sensor is poor, or the sensor is bad (open). Shut off car, then disconnect the connector to the knock sensor. Read the voltage to the connector pigtail (key on engine off). It should be 5 volts. Then ohm check the socket on the sensor itself (to ground); it should be 3.9k (depending on knock sensor used). Run a jumper between the pigtail and the sensor, making sure you have good and solid contact to both. Key on, engine off, the voltage at the connector should now be 2.5 volts. LEAVE THE JUMPER IN PLACE. Disconnect the battery neg terminal again, for a couple of minutes (to clear the code). Reconnect neg battery terminal and with the jumper between the connector and the knock sensor still in place, start the car. If no 'check engine' light within 20-30 seconds, let car continue to run for a few minutes. If still no light, it's the connector that is bad. It could be the pigtail, or the sensor connector itself. I repaired mine without changing the sensor.