so i have a 99 civic si running a p28 chipped, i want to go back to obd2 to pass smog when i plug in the stock ecu it works, the car turns on and runs just cel comes on. i bought the car like this already, so i want to know how to go back to obd2 it has the stock engine harness because it plugs in to the stock ecu but the p28 has like a jumper it plugs into that is attached to the ecu. so any suggestions on how to go back, so i can pass smog. please help.

 

plug in the stock SI ecu, and find out what code it is throwing..

 

it says o2 sensor and air temperature sensor i replaced and reset still get the codes im thinking it was repined or something.

 

oh and cel dosnt blink the srs does, i cant explain that.

 

So according to this Im missing a few wires from connector B for the obd2b. Im missing #6,7,8, and 15. And from connector C #6, which ones do I need. because im not sure if i need them all or just #6,15 and the one from connector c please sombody help me out. and if ther not there does that mean that i have to rewire them or are they probally cut somewhere up alittle bit?

 

anybody with obd2 to obd1 how did you do it and explain to me so i can go backwards thanks in advance.

 

And how would i know if he only used the jumper harness and didn't change anything else in the car. Becasue my stock ecu plugs in the car turns on and drives fine, the only thing is check engine come on and it wont go away.

 

bump

 

I've converted OBD2 cars to OBD1 and OBD1 cars to OBD2.
It's not that difficult, really.

the codes you're seeing, just go through them like you would any OBD2 car.
O2 - primary or secondary? I'm betting secondary since OBD1 doesn't use it. You may have to add one into the exhaust.
IAT - no idea since OBD1 uses the IAT as well.

 

probably throwing one of 2 or three codes
since yours is a obd2b car its probably all three

one for the air temp sensor that is pre throttle body, hopefull no one cut the plug from the harness and you can just put it back and plug it in

one for secondary o2, should just have to put it in the exhaust and the wires should be hanging there under the car

one possibly for crack flux sensor. (on the oil pump behind the crank pulley) again, stock your car should have one. depends on if they uplugged/removed, or swapped to a diff motor/block whatever.