nexgen91

Got a B18CR swap in my 96 Civic DX, and a CEL code 10 for IAT that will not clear, I have replaced the senosr with a brand new one and a known good sensor and its still there, checked voltage at sensor and got 14 VDC, contacts are clean as well. When I disconnect it the engine idles weird, hook it back up and back to normal. I have reset the ECU numerous times and the CEL keeps coming back, tried a different ECU and it is still there, no other CELs present car runs fine with the exception of my slipping soon to be replaced clutch. I searched and could not find much info on this code, anything that it might be hiding that I have overlooked? Thanks

HondaPartsHero

What ECU? Which of the IAT's are you using, the one on the manifold or did you reuse the Civics? What color are the wires going to the IAT?

0HAMOTORSPORTS

You may have the incorrect connector plugged into your intake air temp sensor. You should only be getting around 5 volts at the sensor. Here's a quick diag process:

Intake Air Temperature Sensor (IAT)

What color wires are at the IAT plug on your harness? Possibly a photo??

nexgen91

Ill try to get pics up later, the wires chilies are black and green. There is a connector near the dizzy that is the same but with blue/blk trace and black wires. Also forgot to mention I have a 97 ex harness. What color should the wires to the iat be? I also checked the resistance of the iat and its good.

HondaPartsHero

You have the power steering pressure switch connector plugged into it. The EX connector isn't round but square but the ITR manifold has a round style plug. You're gonna have to find that connector on your harness and cut and splice a round style OR get an OBD2 Civic IAT and put it in your intake arm. The colors of the connector are green/blk and red/yellow. The blue/blk and black connector is for the VTEC pressure switch, your ITR engine is JDM so it probably doesn't have one so this won't plug in.

https://honda-tech.com/honda-civic-d...guide-3146770/

HondaPartsHero

Your connector VS the ITR IAT sensor


OBD1 vs OBD2 Civic IAT



What the OBD2 IAT looks like if you put it into your intake arm

nexgen91

Ok did some more troubleshooting and searching here is what I got so far, I have tried both a P73 and P72 ECU, I have the OBD1 style IAT, I dont have a OBD2 one as the car had a OBD1 engine in it before I did the swap.

The wires on the connector are Green and Black:


Here is a pic of the connector close to the IAT that appears to be the OBD2 IAT connector, thing is the wire colors are red/yel and blk/yel:


I tried hooking it up to the IAT but still got the CEL, so I checked for voltage and got 5VDC from the red wire to chassis but not from the red/yel wire to the blk/yel one so I went to the ECU and shot there, it is getting 5VDC from pin D8 (IAT) to chassis ground, and also to pin D11 (sensor common ground). Appears there is a open in the common ground between the splice group and the sensor, but if I try to jumper the sensor straight to the ECU I get the following CELs (- is long, . is short): 10 (-) (IAT), 20 (- -) (Electrical Load Detector) ,and 41 (- - - - .) (Primary Oxygen Sensor Heater) now I didnt have the car running during any of the testing just turning the ignition on not sure if thats why I got the 41 or not but it goes away when I take out the jumpers as does the 20, but the 10 stays. Also trying to jumper the sensor ground to the chassis does not clear the CEL, the resistance on the sensor is within spec, and I tried multiple sensors as stated earlier. Any ideas? Thanks for the help BTW

HondaPartsHero

DO NOT CONNECT THAT TO THE SENSOR, that is the EVAP purge wire and you could either fry your IAT or your ECU as it will send too much voltage to the sensor and possibly the ECU. Look around your harness you should have a connector that looks just like that black one but has green/black and red/yellow, that is the IAT connector. When you find it connect it to a round style plug like you have plugged in to the IAT now.

nexgen91

Which one agree you talking about the one with the blk/yel and red/yel wires? I dont see another one with the wire colors specified, what is the general location of the ex iat sensor in the bay?

nexgen91

Here is a pic of the plug near the dizzy that has the square connector:

HondaPartsHero

That is the purge vent control solenoid. The IAT should be in that general area unless you have it plugged up to something else

nexgen91

In this pic that is the connector with the blk/yel and wht/grn wires is pretty close to there. That is the one that goes to the IAT or the EVAP valve?

nexgen91

Gave up on the connector and rewired it to the ECU and splice group using some spare plugs/pins, got rid of the 10. Im still getting the 20 and 41, is the car safe to drive with those? Any idea what might be going on?

HondaPartsHero

What ECU are you running?

nexgen91

P73

nexgen91

Ok so I think I figured out the 20 and 41, the alternator fuse was blown, replaced it and those went away thing is, the 10 is now back and the engine is offering really high (between 2-3k both cold and warm), unless I unplug the IAT sensor.

nexgen91

Ok I threw the P72 at it just for SnG, the high idle went away (adjusted per directions found on HT) but the code 10 is still there I also got some other code to (w/ P72 attached) I think it was like a 13 maybe something the B18 doesnt have? What are the chances that either or both of my ECUs have the IAT circuit fried? I got it wired straight to the damn ECU connector and Im getting the right voltage at the IAT connector, IAT reads correct resistance as well (three different IAT sensors). When I unplug the sensor the idle changes, so to me it seems like the ECU is sensing it (each of the IAT sensors themselves produced variations in idle speed as well)
Someone got any idea how I can troubleshoot this farther? Thanks

HondaPartsHero

Where did you wire the sensor at the ECU?

nexgen91

D8. That is where the JDM P73 pin out says the iat goes. Got the bottom wire on the sensor (red/yellow) going to D8 and the top wire (closer to clip) going to the blue splice group on the harness. When I put the P73 back in the high idle comes back and still have the CEL 10. With the P72 Im getting a 10 and a 22 (VTEC pressure switch).

nexgen91

Think if I just put a .5k Ohm resistor in the sensors place (just to test it) it will let me know if the sensor is bad (CEL go off if everything is working at least)??

nexgen91

Is there a fuse that may be causing this issue, thinking maybe I am overlooking something?

HondaPartsHero

I'd try to tap the other wire to D11, don't replace it just tap or splice it.

nexgen91

Ok did that and the 10 went away but the 20 and 41 come back, the alternator/sp sensor fuse got blown again as well. BTW I don't have any of the EVAP stuff hooked up, because I don't have it. Any ideas?

nexgen91

Solved:
Splicing the sensor ground wire from the IAT sensor into the ECU harness at D11 caused fuse 15 (Alt/SP Sensor) to blow which in turn caused the CEL 20 and 41. After tearing the whole harness apart I discovered that the original IAT sensor wires had been cut and left inside the harness. I rewired the wires to the connector and re-installed the harness back in the car, which has cleared the code 10, and also the 20 and 41 are now gone.