EH_special

Hello All,

Have a 1994 Honda Civic VX, brand new rebuilt motor, almost all the sensors are new - ECU, IACV, etc. and it is throwing an error code on the 02 sensor (#1). The sensor was relatively new, about 2 years old. I replaced with a new one (5 wire, expensive!) and the ECU light is still on. It comes on immediately after starting the car, even after I reset the ECU. Idle is fine, power is fine, vtec kicks in, however it does feel like it is loading up a bit and little on the rich side. I checked the fuel pressure and it is within normal range. I even had a spare ECU, exact match, plugged it in and it still threw the code. I did get the vtec/temp/gauge plugs mixed up, but when I put them in the proper place it ran fine, with the exception of the ECU O2 code I am still getting..... Appreciate any help!

EH_special

BUMP****

anybody on this?

ezone

You sure it's not code #10 instead of #1?

One long flash vs one short flash, the difference might not be real obvious if you don't have any reference to go by.

If you leave the O2 sensor unplugged you should get a different code (maybe code #48?) for sensor heater circuit fault.....that way you can see the difference in length of flashes (4 long, 8 short) and reevaluate your original code as #1 or #10

EH_special

Thanks for your reply.

Yes, it is a #1 - long flash. To verify, I took the O2 Sensor off, unplugged, motor was warmed up and when I checked the codes - #1 and #41 appeared== Code1 Heated oxygen sensor A and Code 41 Heated oxygen sensor heater. I plugged the O2 Sensor back into the harness. Shut off engine, then I cleared the codes ( disconnected battery, held brake pedal to drain all current from electrical system).. Started car and within about 2-3 seconds the ECU light came back on. Shut off, checked codes and it is this again - Code1 Heated oxygen sensor A.

I guess this test points directly to the O2 sensor as being the problem?...or an engine condition still??? it is a new sensor 5 wire (expensive) never had issues with before It is NGK. Unless you can think of something else.

ezone

Can't really tell......there's a boatload of troubleshooting that can be done to narrow the possibilities.

If you have a FSM follow the trouble chart for D15Z1 code 48, there's a confusing mess to go through with volt/ohm meter that should help if you actually do it...until it says to try a known good control unit. Then you may be screwed unless you have a friend with a clone of your car that actually still works correctly.


Grab a good wiring diagram....... verify continuity of each wire from that sensor to the ecm, power source, or ground as shown by the diagram

(6 of the wires go from ecm to sensor, only one sensor wire goes to chassis ground)




EDIT: Wait, you say only 5 wires on yours? (my diagram shows 7?)
7 wires in the harness plug but connected to a 5 wire sensor will not work
WHat engine does it have?
How recent was this fresh rebuild? How long did it work before this new sensor code happened?
Check all of the harness junction connectors on the fender nearest the battery, maybe not fully latched or corrosion or moisture or terminal damage

EH_special

Just to clarify, the code 41 is what I got when I unplugged the O2 sensor , the code 1 was also still showing. When I plugged the O2 sensor back in, the 41 went away but the O2 was still showing. Which is the issue I am trying to figure out, not a 48 code. Yes, it is a 5 wire (VX) and the sensor was the original one on the car when I got it. It is the correct one for the car. I replaced it with a new NTK unit, exact match.

I do have a Chilton SM so I will go through the troubleshoot for it. I will check the terminal junctions as you said. See what I come up with...

ezone

I was looking in factory service info, I only see 4 wire sensor or 7 wire sensor for 1994 cars. I found nothing referring to 5 wire sensor so far for 1994.

What's your VIN, and what is the engine code on the engine now in the car?

EH_special

At work, so can't check the vin but it is a 1994 Honda civic hatch VX, almost 100% stock, rebuild was about 4 months ago and it is the d15z1 vtec-e with lean burn, and the 5-wire wide band O2 sensor (aka Lean Air Fuel (LAF) sensor)