O2 sensor circuit electrical issue/ Help Please

rickerho

Joined
May 26, 2013
Messages
19
Location
canada
Hi, hoping someone can help me. I have F1 code 24 O2 sensor heater 2/4. I changed sensor cleared codes but code is there immediately. So started going through service manual checks. O2 sensor was in fact ok and so is new one. I have found no ground at White wire with yellow stripe at black plug to 2/4 oxygen sensor. I'm at the point in trouble shooting where it tells you to plug in an ECM test harnes. So I called around to local dealers and they don't have one. Does anyone know where I can find a picture of ECM that shows which pin is for what? From the wiringdiagram in service manual I can't tell which O2 sensor is which nor does it show wire colors...so pretty hard to trace.
Thanks for any help anyone may have.
 
Go to this site and download the Setup Instructions for the 2004 ST. Open the file, or better yet save it and then go to the end of the document to view the schematic for either the ABS or non-ABS version. The O2 sensors are at the far upper right hand side of the schematic.

The black plug for O2 sensor 2-4 shows White and a Black/White wires connected to the heater. Green/Orange and a Black/Orange wires connected to the sensor.

One thing I noticed after looking at both the schematic and then the troubleshooting section for code 24 was that they refer to a White/Yellow wire in steps 4 and 5 for the negative connection. Well there isn't a White/Yellow wire used anywhere in O2 sensor 2-4 according to the schematic so one of those documents is wrong. (Note: I'm referring to a 2003 version of the service manual. Perhaps it has been corrected and updated). I think they meant making the negative connection to the White wire instead.

I haven't been able to find a pinout of the ECU connectors for the early version of the ECU (used 2003-2007 IIRC). If you look at that link I provided earlier and download the setup instructions for the 2008 ST you will see the schematic in this document shows a pinout of the ECU. However this ECU is using 33 pin connectors whereas the older ECU uses 26 pin connectors.

Good luck and keep us posted...
 
Thanks for the information Scooter! You're exacrly right the ground wire is white not white /w yellow. Now my problem is where does that whie wire come from? According to diagram it goes to ECM. If ECM is above rear wheel then there are no white only wires there? Any idea where this ground comes from? I'm thinkng it must go through a conector some where and change colors? Do you think Honda will give me this information? The dealer doesn't seem to have any more information than what Im showing in manual and what you provided.
 
So finally fixed this...ends up there are 2 white wites at ECM but they looked yellow. So there was a bad conecction at ECM for white wire that provides ground to 2/4 oxygen sensor. Repaired and now code 24 gone.
Still wish someone could provide me with a pin out diagram for these 26 pin connectors as that would make trouble shooting so much easier.
 
Glad you got this problem sorted out, now I hope you can get out and ride before winter sets in.
 
rickerho said:
Still wish someone could provide me with a pin out diagram for these 26 pin connectors as that would make trouble shooting so much easier.
Click to expand...

At least part of it can be divined by looking at the color of each wire and comparing it to where it goes on the wiring diagram. Some of it can also be picked out from the service manual, as I'm pretty sure the pinout of the test harness is the same as the connectors.

--Mark
 
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