After rebuilding the car after painting I've been driving about for few days and everything was fine. Today SES light came on during driving and it went away few seconds later... It came on few more times after that so once at home I checked the codes and it shown code 43 (ESC). Is this caused by knock sensor? Should I change it? The car drives just fine, no loss of power or any other suspicious issues.
I had all the wiring out for painting but everything is now connected properly (I hope), and the knock sensor connector looks fine.
I will order new knock sensor anyway but maybe someone has got some other ideas?

BTW
The car is 91 Z28 305 TPI code"F"

Thanks for your help.

 

Might be the EST wire - the one that you disconnect to check/change timing - maybe it got disconnected.

 

Either the sensor or the connector/wiring. The sensor resistance should be about 3.9 K ohm (3900). Can measure it with the connector off between the center terminal and the sensor body or engine block.

Note that the sensor is in the water jacket, so expect coolant when removed. Although, sometimes enough 'stuff' has built up in the lower area of the water jacket that it won't leak much.

If the EST/BYPASS connector was open that would set code 42.

RBob.

 

Thanks for that. I've ordered new knock sensor anyway just in case.
When I was putting the interior of the car back (just minutes ago) I closely inspected my ECM (it's lying in the passenger footwell) and one of the three big connectors was not on properly. I pushed it in until it clicked, I will go for a drive later on to see if it helped.
Once the knock sensor arrives I will change that as well, to be on the safe side

 

Any updates?