Check engine light...

:biggrin: Hello, I recently got a b16a1 swap in my 1990 civic HB SI, I know that the stock wiring harness was used in the swap. I was wondering if the engine light could have something to do with the ECU looking for an oxygen sensor I don't have. I believe there is one sensor on my exhaust now, but the ECU is looking for 2. Does this sound logical? Is there a way I can fix it without adding another O sensor? (which my exhaust I believe only has a hole for one sensor) I have DC Headers and Apex exhaust. Any help would be great! Thanks!

Um either you have the wrong ecu or your o2 sensor is bad what ecu are you running?

I believe it's the pr3 ECU. The car runs a little rich but not too bad really. I thought that the 88-91 civic's in japan were made with 2 O-sensors instead of 1 like the usdm version. But i'm not certain.

no obd0 and obd1 had one o2 sensor. obd2 had two o2 sensors

obd0 has 2 o2's...mine are spliced together and I dont throw any codes but I do run rich. Best thing to do is have a shop weld another bung on and hook the second o2 up. Before any of that I'd count the number of times the light on your ecu blinks and find what code it is throwing...unless you've already down that.

obd0 has 2 o2's...mine are spliced together and I dont throw any codes but I do run rich.
yeah my bad, i was thinkin of D-series.

Ok thanks guys, I will try that and see if it helps any. I will let you know what code my ECU is throwing as well. Thanks for the help!

Well my ECU is flashing a code 23, if i'm reading it right. It flashes long 2 times and short 3 times. If this is correct isn't that a knock sensor code? It is the only code it throws but i'm not sure if they only throw one at a time or not.

if the engine is running fine, just take the light off the dash where the check engine light is that should fix ur problem!

lol jk : P Make sure u didnt accidentaly get an auto ecu if you have a manual tranny, sometimes that can throw it off

Hmm... if you have a PR3 you do not have a code 23, no such animal. You have a code 10(Intake Air Temp Sensor) and a code 13(Atmospheric Pressure Senor also called PA sensor).
The codes are thrown in a repeating series in your case I think its doing this:
Flaaaaaassshhh_________Flaaaaaassshhhh_flash_flash _flash__________then its repeated Flaaaaaassshhh_________Flaaaaaaassshhh_flash_flash _flash__________ over and over until ya fix it. On the long pauses you can almost count to 3 before the next code is thrown, short "pauses" are very quick like as soon as the light goes out it comes right back on.

Mojoe (Hmm... if you have a PR3 you do not have a code 23, no such animal.)

- i'd say you are wrong. When I turn my ignition key to the on possition, my ecu flashes once quickly, to let me know it's working, after that I get: Long,Long,short,short,short (long pause count to 3) Long,Long,short,short,short, over and over again. Which to me means i'm throwing a code 23 which is my knock sensor code.

PR3 ecu codes

1) Primary oxygen sensor- Defective circuit or unplugged/ Defective sensor
2) Oxygen sensor "B" - Defective circiut or unplugged/ Defective sensor
3) MAP (Manifold Absolute Pressure) Sensor - Defective circuit or unplugged/ Sensor
4) CKP (Crankshaft Position Sensor) - Defective circuit or unplugged/ Defective sensor
5) MAP (Manifold Absolute Pressure) sensor -Mechanical problem/ Disconnected piping
6) ECT ( Engine Coolant Temperature) Sensor- Defective circuit or unplugged/ Sensor
7) TP (Throttle Position) Sensor -Defective circuit or unplugged/ Defective sensor
8) TDC (Top Dead Centre) Sensor -Defective circuit or unplugged/ Defective sensor
9) CYP (Cylinder) - Defective circuit or unplugged/ Defective sensor
10) IAT (Intake Air Temperature)sensor- Defective circuit or unplugged/Defective sensor
12) EGR (Exhaust Gas Recirculation) -Defective circuit or unplugged/ Defective sensor
13) Atmospheric Pressure Sensor - Defective circuit or unplugged/ Defective sensor
14) IAC (Intake Air Control) Valve- Defective circuit or unplugged / Defective sensor
15) Ignition Output Signal - Missing or defective ignition output signal
16) Fuel Injector System - Defective circuit or unplugged/ Defective fuel injector
17) VSS (Vehicle Speed Sensor) - Defective circuit or unplugged/ Defective sensor
19) Automatic transmission lockup control Solenoid Valve- Defective circuit or unplugged/ Defective solenoid. A/T Only.
20) Electronic Load Detector - Defective circuit or unplugged/ Defective sensor
21) VTEC Solenoid Valve- Defective circuit or unplugged/ Defective solenoid
22) VTEC Oil Pressure Switch - Defective circuit or unplugged/ Defective switch
23) Knock Sensor - Defective circuit or unplugged / Defective sensor
30) Automatic Transmission Signal- Defective circuit or unplugged/ Defective sensor
31) Automatic Transmission Signal "B"- Defective circuit or unplugged/ Defective sensor
41) Primary Oxygen Sensor Heater- Circiut malfunction
43) Fuel Supply System - Defective or malfunctioning Fuel Supply Sytem
45) System too lean or too rich - Malfunction in the fuel monitoring systems
48) LAF (Lean Air Fuel) sensor - Defective circuit or unplugged / Defective sensor
54) CKF (Crankshaft Speed Fluctuation) sensor- Defective circuit or unplugged / Defective sensor
61) Primary Oxygen sensor circuit- High/ Low Voltage, Or slow response
63) Secondary Oxygen Sensor circuit- High/ Low Voltage, Or slow response
67) Catalyst System Efficiency Below Threshold- Malfunctioning catalyst system
70) Automatic Transmission - Malfunction with Automatic Transmission Controls
71-74) Random misfire in Cylinders 1-4- Condition present Creating Misfire
80) EGR (Exhaust Gas Recirculation) Insufficient Flow Detected
86) ECT (Engine Coolant Temperature) Circuir Range / Performance Problem
90) Evaporative Emissions Contrlo System - Leak Detected In Fuel Tank Area
91) Fuel Tank Pressure Sensor- Low Input
92) Evaporative Emission Control System Control System- Insufficient Purge Flow


i would have to say you are correct

oh and btw u sould get the second O2 sensor in there all u have to do is go to a parts store or muffle shop and get a O2 bung and weld it to ur header

Thank you for the list, the list I have is in my 90-93 integra haynes manual. There is no hole on my header for an O2 sensor. Would it be feesable to just hook one up to my ECU and leave it laying next to the ECU or something?

u need both O2 sensors hooked up just run by ur local muffler shop and ask them they sould do it for cheap the O2 bung is only like 5 bucks at most and then it just drill a hole and weld it on

if you dont wanna bother with hooking a second one up, then connect both wires to the same sensor. yeah, its not exactly the ideal setup, but its better than nothing hooked up at all.


and about the knock sensor code, the only possibilities are that your sensor is bad (highly unlikely, they detect vibration, so its doubtful it rattled apart on the inside, unless you hit it putting the engine in), the connections arent well done (butt connectors instead of soldering), or not using shielded wire (this is a lot more important than it seems)

I only used one O2. I had the shop clogged the second hole on the down pipe.

Well I took the knock sensor out of my spare block and replaced it in the new one and all seems to be ok. My ECU has stopped flashing me the 23 and all seems to be ok with my electrical system now. Now all I have to do is put my front end back together and have it inspected and I should be able to get my title for it. It's been a rough couple of months but i'm finally feeling like it's going to be a victory. hehe. Thanks for all the help!!

EDIT -- Nevermind, it's still throwing the code. It wasn't in the beginning but after warming it up and everything it's still throwing the damn 23. My idle also seems to be fluctuating from 1k to 2k after my engine warms up. When warming up it runs at about 3.5k RPM...does this seem high to anybody else? I know I need to replace my PCV valve because the one I have now is broken. But I still can't figure out this damn code 23...could it be because it's not wired with shielded wire??

yes, shielded wire is a must