platanaso47

Hello everyone here's my issue.

the car:
i have a 99 lx 4 door auto, with a mini me swap.

the problem:
i bought a 99 ex wire harness, obd2a p28 ecu and obd2a-obd2b jumper harness. my problem is im throwing a cel for 02 sensor. when i bought the car the man told me the sensor was bad, so when i went to change it, i saw the wire harness has no 02 sensor connector in it. so i ordered a 2000 ex wire harness and lo and behold it also has no primary 02 sensor connector...wtf? i looked at my cousins civic 96 and right by the distributor there are 4 wires and 1 of those wires connects to the top 02 sensor....whats going on here? how come my wire harness only has 1 02 sensor connector...and also i checked the part number on the engine harness and it is in fact for a 99-00 civic ex. i thought it was from a eg chasis but the part number is impossible. i need help before i shoot this car. i just wanted a stock civic, but i get this!!! any diagrams, any info would help...i will even post pictures of the harness if need be!!

fleabag

Well there are a few things you should know.. One, ALL CIVICS HAVE TWO O2 sensors, period, just wanted to get that out of the way. Alright, secondly, you should understand how the catalytic converter setup differs from the DX/LX/CX, HX civics with the D16Y7 or D16Y5 engine and the Civic EX with the D16Y8 engine. The civics with the Y7 and Y5 have the same type of catalytic converter which is a 4-1 integrated exhaust manifold with catalytic converter. This allows for quick warm up and lower exhaust emissions. Now the EX civics with the Y8 engine have the standard exhaust manifold that then leads to a catalytic converter down stream.

Alright, so this difference is important and I will tell you why. The civics with the Y5 and Y7 engines, since the catalytic converter is just right off the engine, the Primary and Secondary O2 sensors are on the same engine wiring harness. One on top of the cat and one just below the cat. However, the civics with the Y8 engine the Primary O2 sensor is just at the exhaust manifold while the secondary O2 sensor is located part way down the underside of the car, just after the catalytic converter. This means that the Secondary O2 sensor harness can not be found on the engine wiring harness for the Y8 engine. Instead, this sensor harness is part of the interior cabin harness which drops down through a hole in the area of where the shifter is. This also means that the cabin wiring harness that came with your Civic LX (D16Y7) would not have an O2 sensor wiring harness that comes off the interior cabin wiring harness since that sensor harness is integrated into the engine wiring harness for that particular engine.

As for you not being able to find ANY O2 sensor harness on the primary harness, well it should be there unless it has been cut from both harness' you've looked at since there should be at least one O2 sensor harness off the engine wiring harness due to the location of the PRIMARY O2 sensor. Have you actually tried looking up the check engine code to see which O2 sensor it is looking for? If you have to pass emissions in your area then you'll definitely have to get both sensors working but if not, then at least try to get the primary o2 sensor working, otherwise the car will not run optimally. Are you sure you didn't just plug in the O2 sensor plug into something you weren't suppose to plug it into and that's why you can't find it? There should be AT LEAST one O2 sensor harness off the main engine wiring harness.

As for you not having a secondary o2 sensor harness, you either should replace the interior cabin harness with that from an EX or you should go back to your stock Y7 harness and then run an extension from the secondary O2 sensor harness all the way back to where the catalytic converter is.

HondaPartsHero

Actually to clarify ALL OBD2A/B CIVICS HAVE TWO O2 sensors. This for 96up civics/integras.

But I agree with Fleabag on just using your LX harness and making the necessary adaptations to a few of the sensors, namely: extending the two O2's, wiring up the 2 wire IACV (see links below), and adding VTEC and knock sensor. The easiest plug and play method aside from this is to get a 96-98 EX engine harness and then just wire directly to the ECU plug the secondary O2 wiring. Although you will still need to do a similar exhaust setup for the manifold and cat to have the correct secondary O2 routing. If you have any wiring questions feel free to PM me or check my sig below for any wiring help.

4 wire secondary O2 wiring
http://ff-squad.com/wp/?p=395

3 to 2 wire IACV
http://www.ff-squad.com/tech/wiring/wiring.96-98.jpg

fleabag

Well, any Civic with a catalytic converter has two o2 sensors, one to measure the mixture before the cat and one to verify the catalytic converter is working. I don't know how they did this for late 70s early 80s cars that are carbureted and don't need the O2 sensor to adjust fuel mixture, but they definitely need one to confirm the catalytic converter is working, so that when it stops working, you get a check engine light for that.

94EG8

No. OBD1 vehicles don't have a secondary O2 sensor after the catalytic converter. They also wont throw a CEL for a bad or non existant cat because there's no way for the ECU to monitor it.

BryanM.

iTrader: (1)

OP if I were in your situation I would run wires from the 02 sensors directly to the ECU.


Some people need to have the internet taken away for them when they start typing stuff they know nothing about. Especially in a tech forum.

HondaPartsHero

As well as OBD0 (non OBD as some call it). Pic for reference below. Notice in the 92-95 there is no secondary O2. Also the pic for 99-00 EX shares the same picture with the 96-98 EX however the primary O2 location for 96-98 EX civics is higher up on the exhaust manifold. For 99-00 the primary O2 was placed right before the catalytic.

92-95 EX (D16Z6) Exhaust



92-95 EX (D16Z6) Exhaust manifold



96-00 EX (D16Y8) Exhaust



99-00 EX (D16Y8) Exhaust manifold



96-98 EX (D16Y8) Exhaust manifold

fleabag

****, you're right.. I must have confused vehicles.. I just checked the service manual for a '92 Civic and I couldn't find any secondary o2 sensors.. I guess my 1991 LS400, despite being OBD-1, has 4 o2 sensors.. There are a few 70s and 80s vehicles that have o2 sensors despite being carbureted I know that much.

94EG8

Forgot about OBD0, but yeah. Before anyone mentions it some OBD0 engines (B16As for example and I think some '88 - '91 Preludes) had 2 O2 sensors, but they're both primaries.

platanaso47

yes you have a point fleabag. there is 1 02 sensor on the wire harness. the reason i bought the EX engine harness is i thought with the mini me swap that i would'nt have to wire the vtec...since its already in the wire harness, but now im missing the 02 sensor connector. when i lay my wire harness in the car, the 02 connector seems to lay closer to the back of the engine...after reading what you posted i thought it would sit in the front of the motor to connect to the manifold connector. now if i manage to connect the plug to the front of the car, can i run a wire from the secondary to the ecu pinout? my car is throwing a code for both 02 sensors, the one on the top is disconnected and im assuming its throwing off the second one...hence why it is throwing to cel and yes i need to pass emissions since i live in pa, im actually 5 months overdue on emissions. im going to send a picture of the wire harness and show which 02 sensor im talking about.

HondaPartsHero

Good call

apexi_rsx

Your right the Y8 harness only does have one O2 sensor connector on the harness but the motor has 2 O2 sensors. It's because on a Y8 Wiring Harness the secondary O2 Connector is ran into the floor harness. i ran into this same problem a long time ago when i had to buy a new harness. you may have to depin the one from your old harness and intergrate it into y8. that's what i had to do.

platanaso47

thanks what im going to do is get the wire and pin them to the connector that i have (extra one) and plug it directly to the ecu. im going to run it to an obd2a from a del sol 97...with an obd2a to obd2b jumper harness. the only issue that im having is that the 02 sensor connector does not reach to the front....it reaches more to the rear of the car....is this correct? thanks for the help guys, this is my first post and already im getting knowledgeable answers. apexi if you remember the pinouts that would be a great help and parts hero i might hit you up to buy the extension if i dont get the 02 cable to reach the front of the motor.

platanaso47

apexi do you have any info on how you did that? im having my cousin do the pin for me on my p28 obd2a but im kinda worried that it wont start, cause it was running before on a p2p. anyways hope i get this running before the snow storm.