Hello All,

I have a 2004 RSX Base engine/wiring installed in 2002 Insight. Just got it running after issues with transmission noise. I took extreme care in wiring, checking each circuit with DMM 3 times.

ECM/PCM won’t go into closed loop, throwing MIL codes P0135, O2 bank 1 sensor 1 heater malfunction and P0600, communication issue. This is a Wide Band Air Fuel Sensor. Checked fuses, battery voltage on both. Checked grounds, .2 ohms on both A4 and A5 to G101, the main engine ground on the intake manifold. Please see the diagram below:



[img]file:///C:/Users/Bob/AppData/Local/Temp/msoclip1/01/clip_image002.gif[/img]
Above the red line is 02 Insight, below it is 04 RSX.

I am not getting any voltage at C101-6. I AM getting battery voltage at ECM/PCM E8. This means the heater circuit is working, just not being turned on by the ECU.

What this is telling me is that the ECM/PCM is NOT grounding the heater control at E8. It is grounding the PGMFI Main Relay control, and the engine runs fine, although no closed loop.

Is there someone there that can give me some hints as to why this ECU is not turning on that heater?

 

I just spent some time mucking with O2 sensors... it won't ground the relay if that code is up. You can try clearing the codes and trying again, but it knows very shortly after "Key-On" if the response rate of the heater circuit is incorrect and it will just store the code again. The fix is replacing the sensor. (or try a known good sensor)

From the manual "Deterioration of the primary HO2S can be evaluated by its feedback period. When the feedback period exceeds a certain value during stable driving conditions, the sensor is considered deteriorated and the ECM sets a DTC" That sounds like the sensing element deterioration to me, but based on my experience I think it does a similar thing with the heating circuit. The temperature of the sensor is important and it uses PWM on the ground side to adjust the sensor heater current to maintain a temperature... as I understand it, this is part of why the primary O2 sensor is fancier than a normal 4 wire sensor.

 

Thanks for the reply, That is the direction I was heading. I had read that on other Honda ECUs, that O2 sensors having too low resistance across the heater coils have been known to take out that part of the ECU. That is a worry here. But if as you say, "it knows very shortly after "Key-On" if the response rate of the heater circuit is incorrect and it will just store the code again", then there is hope that circuit protection exists in the computer. Honda has been known for having very reliable computers.
Thanks again.

 

Keep in mind that the factory O2 sensor is very sensitive to vibrations. If you've dropped the sensor or something fell on it, it is probably bad. Also, if you start the car on an open header (without it secured somehow to minimize vibrations) or without the exhaust secured properly, the vibrating or shaking exhaust/header will also ruin the sensor fwiw.