chevy383

Ok so to start off when i got the car (98 civic dx d16y7) the plug connector for the IAT sensor was nowhere to be found. Got a connector end and found ecu wires for this sensor where they came through the firewall. Now my IAT has a reading as do all other sensors but the readings are not accurate i dont think. Car runs decent but not full potential.
CEL codes:
P0118 ECT temp sensor 1 circuit high
P0113 IAT sensor 1 circuit high
P1108 BARO sensor circuit high
P0135 o2 heater circuit B1S1
P0141 o2 heater circuit B1S2
sensor readings:
ECT=77°F its about 30°outside and car been sitting for hours
MAP= 14.2PSI
VSS= 158MPH
IAT= 66° its actually 30°out
TPS= 11%
O2 B1S1 1.275V
O2 B1S2 1.275V
All of this is with key on engine off and car has been sitting for at least 4 hours now. Any help with getting the sensors to read more accuratly will be greatly appreciated

Former User

What ECU? The ECU may be bad.

After resetting the ECU, do all the codes return?

Is 7.5A dash fuse 15 blown?

chevy383

It is a P2E. and have not checked fuses. I thought that maybe from me splicing into the sensor ground for the ecu that i had thrown all of the other sensors off a little from the draw of the IAT sensor or from the butt connector but i did use good heat shrink butt connectors and someone on here showed me to a link for ecu pins and it was connector D cant exactly remember pin numbers but it was like d8 and d11 or d12 if im not mistaken. Pulled connecter from ECU put one probe from voltmeter on the pin i needed and went through the wires under the hood and found the one that showed continuity and ran the sensor strait to those 2 wires. From the looks of the 2 blank plugs behind the motor near rack and pinion that sensor ground goes to that blank plug connector and splits to the other sensors right? I think that may have something to do with it but not sure what the correct way to get them back right would be. Dont think it is ECU because i didnt have all of those codes before and anytime i was working with the wires battery and ECU were disconnected.

chevy383

And yes the codes return right after

Former User

Based on this^ information, your rewiring could be the problem or it could have blown the ECU (or both).

Did you check fuse 15?

chevy383

Not yet. It will prob take me a few to get out there and check it. Do you have any information you could share with me on how those blank connector plugs work. The one i believe i would be dealing with had about 5 black wires and about 5 green and black i believe. If i am thinking right on what i saw looking at it it takes like one black wire comming from ECU and splits it into 4 or 5 other wires to go to other sensors and whatnot correct?

Former User

They're junction connectors. Why are you focusing on them?

chevy383

Correct me if i am not thinking in the right path because i am a little puzzled. But ECU pin d8 is IAT wire which is a 5 volt reference right? Well that wire goes directly from ECU to IAT. well the other wire from the IAT goes back to d11 which is sensor ground green/black. But that is not just the ground for the IAT is it? If i am in the right mindset from what i saw there is a group of green/black wires on one of the junction connectors. So the sensor ground comes from the ECU and into the junction connector and then out to other sensors. So since i made like a T into the main sensor ground before the junction connecter could the butt connector or possibly even the fact that i should have just spliced into that sensor wire before the junction instead of after not have an effect on the voltages of all of the other sensors that use green/black grounds? If i am completely wrong then please tell me but it seems like that could play a roll in it since i am getting readings from all of my sensors they are just inacurate.

Former User

Yes

Correct

Correct. It's junction connector C115.

Post pictures of your splice job. Theoretically, all Grn/Blk wires (pins 8-14) at C115 are equivalent.

chevy383

I will when i go out to check fuse. Still getting the kids to bed. But basically i took tape off of harness near passenger side strut above the transmission. Found the green/black that had continuity back to ECU pin d11 and put a butt connector there. One end bof butt connector with one end of green/Black which is the end that goes back to ECU. Other end of butt connector has opposite end of green/black going to junction connector and then another wire along with it that i added to go to the IAT valve since someone had hacked the connector off and i assume taped the end of the wires that were left up inside of the harness. Other wire from the IAT connector i did the same and found the red/yel wire in the same part of the harness i cut open and spliced with heat shrink butt connector and ran wire from there to the red/yel on the IAT connector. My hopes were to bypass having to cut the whole harness open searching for 2 wire ends in there and just splice into them right after the fire wall where i was positive i could find the wires at and run them strait from there to the IAT. My concerns with the wiring were if the size of wire i used would have an impact on it since what i used was just a little bigger than the factory wire. And if using butt connectors on sensor wires could be impacting me since i would guess it wouldnt take a whole lot of voltage change or ground change when only dealing with 5 volts in the first place to make a noticible difference in the actual readings the ECU gets back from those sensors.

nub

Chevy, you're correct on your pin outs and and D11 being shared through the junction by other sensors. In think you have codes for all of the sensors sharing it that apply to your engine/ecu.

I think you need to go back to your IAT ground connection at the ecu. You may have a bad splice on the ecu side preventing the ground signal getting to everything down stream.

chevy383

I was thinking maybe i needed to soulder the green/black wire back together and put some heat shrink over soulder joint and then find the wire comming out of the junction connector for the IAT and cut it after the junction and solder a piece of wire from the junction connector to the IAT connector instead of splicing in before the junction as i did the first time. I have experience with wiring but never got to deep into sensors and things like that. So i was unsure if the size of wire i used and butt connectors instead of soulder and any other variables that i could have thrown in by not going through the junction could cause me to have noticible differences in sensor readings the ECU recieves

chevy383

I will try this tomorrow when i get off. The car drives well but just seems like it isnt up to full potential and with my scan tool on it i could just tell some of the sensor values were off and wasnt sure of which things i should change/avoid doing when wiring up sensors.

chevy383

Is there a good schematic you could link to me for this so i can have one to refer to. Ive been able to find most of what i needed to find but not all in one place and going back and forth between 5 websites and diagrams gets confusing. I even have access to alldata and couldnt find what i wanted as far as a good lay out of sensor to ECU wiring

Former User

Among the CEL codes, only the ECT and IAT share the Grn/Blk wire ground. The O2 sensor heaters and the baro sensors do not.

I suspect the ECU may be bad, but the wiring first must be fixed, if needed.

For example, when the baro code is thrown, you generally must replace the ECU.

Have you checked fuse 15?

nub

You'r right Ron. I know the baro is internal to the ecu. I was thinking about the grn/blk sensor grounds for the O2's but those go to D13, sorry.

Shouldn't he be throwing a VSS and ELD code if fuse 15 was blown?

I Think it'd be worth finding the original IAT wires, they can't be cut off that deep in the harness.

chevy383

Have not checked fuse yet. It is now pouring down rain but will when i get to work in morning and can pull into the shop. Will that fuse throw crazy codes? I know fords can blow a 5 amp fuse and have tons of codes thrown. Im new to the hondas

chevy383

My vss was reading 150mph on scanner with the key on engine off

Former User

Yes, both O2 sensor codes and the ridiculous speed reading could be due to a blown fuse 15. Replace the fuse if blown and make sure it doesn't blow again.

However, be prepared to replace the ECU.

Former User

A blown fuse 15 can inexplicably throw some but not all codes for sensors on the fuse 15 circuit.

chevy383

Well my second o2 is going to throw a code regardless because of the header and havent done a defouler or simulator yet. But front o2 shouldnt have a code. Both o2 were brand new when i got the car not to long ago. And i only had downstream code at first

Former User

Are you refusing to check fuse 15?

chevy383

No that will be first thing i check when i get to work in the morning. Took forever to get our 5 month old twins in the bed and now its pouring rain.

nub

Chevy, your secondary O2 code is for the heater circuit. The defouler won't do anything to "fix" that. The defouler is a work around for a P0420 which is a insufficient catalyst code.

This could tie into Ron asking about fuse 15 which supplies key on power to the primary and secondary O2's blk/yel wire for the heaters.

chevy383

Say the BARO is bad. All the rest of the ECU should still function right? How much does the BARO really effect performance and Drivability. I went to anderson today. About 35 miles away and ran like a champ. I just have a slightly high idle and feel like i am lacking power from false sensor readings