check engine light went on couple days ago,my truck is a 91 22re..Scanner could not make a connection which is weird to me, so just did the jumper wire..I got three codes 12(RPM signal) 21(02 sensor signal) and 43(starter signal)

I noticed that my code 12 and 43 share the starter signal circuit, is that a clue it could be something in the starter signal circuit? is 21 usually just the 02 sensor?

just looking for some advice this is the first time my truck had the check engine light come on..TIA

 

Reset the ECU and see which come back after a day or two of driving.

 

Is your truck even starting and running? If the truck is cranking then the starter signal is kinda a miss code you could say. Rpm signal is showing up usually pops up when the truck won't start and miss communitcation to ecu. You need to try what abe said first and reset the computer. Pull EFI fuse and disconnect bat for a good bit. Your o2 is prolly just bad or you got vac leaks and or exhaust leaks.

 

truck runs fine, but i have had a starting problem for some time..I could never find it so i just jumped the soleniod to a hot wire and put a push button in between the two in the cab..I replaced the starter, starter relay, and my clutch switch is good..when i turn the key you can here the fuel pump and thats it, it won't turn over..so thats why i installed the push button

02 sensor is probably bad it is the original, and I will try reseting the ECU