Bear with me. New here. Hopefully I posted in the right section..

1999 prelude SH, I've got a Check Engine and ATTS light that comes on a moment or so AFTER the car starts. The lights are not present at any other time apart from when the car is running. The car has vibrant headers, megan test pipe, DC exhaust, cold air intake, and a VAFC. The car was tuned by a reputable shop with this setup by the PO. Both 02's are hooked up.

So here's the deal. Took the car to both advance auto parts and autozone to have them run an obd 2 scan on it (definitely obd 2, no swap as far as I know), both with and without the car running (since the lights don't appear until the car is on). Tester showed no codes (CEL and ATTS lights were clearly visible). Tried a reset and lights were still on.

The car runs excellent except vtec doesn't seem to hit as hard as it should. Solenoid gaskets are good and filter is clear so I am attributing the vtec condition to the CEL. Because of this I am guessing I have a secondary 02 issue? I have no clue whether it is a bad 02 or getting bad readings because of the test pipe.

Going to try something like this before I take it to a dealer and let them run a Diagnostic on it. Going to get out the multimeter and do some testing first though.. BLOX 02 CEL Eliminator

I'm thinking I know what the issue is with the 2nd 02, but I want to be sure. I have tried jumping the CEl and ATTS codes from the manual jumper and still get nothing. It just doesn't make any sense to me why I cant get codes from the car?? Is there a way to test the OBD 2 plug and make sure it is functioning correctly? Shorts are common in them so I hear. Or possibly the PO has swapped to an OBD 1 setup??? That was never mentioned but who knows?

 

The idea of the car being switched to an OBD-1 style ECU has potential... the common symptom of a dead diagnostic port where there is power present (powers up a scan tool) but no data stream exists makes logical sense. It is possible that the single data wire is damaged, but unlikely. An OBD-1 ECU will not communicate with the diagnostic port and thus, no data will be relayed to you. Also, the ATTS system gets no instruction from an OBD-1 ECU, so the system trouble light will be illuminated on the dash. You can check MIL codes manually by using the service connector and a paperclip.

The obvious fix would be to re-install a "SH" ECU from a '97-01 (insert your car's model year here) Prelude and have the immobilizer married to the new ECU and existing key. The problem with this choice is that since you have a test pipe in the exhaust system, you will ultimately get a CEL for a 2nd O2 (catalyst in-efficiency). You can try to use a de-fouler to remove the sensor from the direct exhaust stream, but positive results using this method are hit/miss.

Pull the carpet back and expose the ECU... take a pic and post it here so that we may help you better.

 

Back from the dead! havn't had any time to dig into this until today.

Shot of the ECM. There are spliced wires are for the Vtec AFV Controller installed by the PO. I assume so anyways.. There is a loose red wire that runs to a N02 switch that is not hooked up. Other than that everything looks good.



Also found this guy unplugged. Not sure if it's related. Looks like emissions solenoid maybe?? I don't know what it is or where it goes. The two hoses on the left go to the throttle bodies. the plug goes down into the passenger side of the bay towards the cab.