Need help with p0135 CEL

dcintron3790 · May 16, 2017

Hey guys I have a 1999 Honda Accord LX ULEV F23A4 2.3L Automatic. I was getting a CEL for the code p0135, I did some research and found out it was for the o2 sensor, or Air/Fuel ratio sensor to be exact since my motor is the F23A4 model. I purchased a new sensor which is the Denso 234-9025 Air Fuel Ratio Sensor from Advanced Auto Parts. On Amazon I looked at the reviews of that exact sensor and there is a lot of positive reviews specifically for the engine that I have. I also tried to test the voltages and continuity coming from the harness and on the sensor itself. Everything comes in normal, so I am wondering what else can I test for? Still currently getting a CEL. p0325 has just popped up as well. Not sure if they are linked.

dcintron3790 · May 16, 2017

Update:

I narrowed it down to the PCM/ECM module, the connector 31p which is the blue connector is missing a black/white wire. I've looked up the pinout and the wire that is missing is for the PO2SHTC (Heated Oxygen Sensor). Seems like someone has been tinkering down here as well, I see some exposed wiring. I tried to find the missing black/white wire but I am not seeing one. I also notice the harness going into the oxygen sensor has a black/white wire, but I am unsure if the connection stops elsewhere before going into the sensor itself. I've tried connecting a new wire from pin-1 to the harness going out to the o2 sensor, of course I reconnected all of the connectors back into the PCM. But I still get the check engine light. My guess is that its not the same black/white wire.

dawg316 · May 16, 2017

did you erase the code after the repair?

p0135 is for the heater circuit in the o2 sensor. not fimiliar with the ULEV wide band o2 sensors but the o2 harness should have 2 wires similar colour usualy 2 green. those 2 will be the heater circuit.

the ecu will send 12v power to the heater circuit durring the open loop timer when engines cold for lets say 30-60 seconds before it switches to closed loop

when you checked your voltage did you see 12 volts coming into the o2 sensors?

see if the ECU is supplying the 12 volts at the ecu pin

dawg316 · May 16, 2017

using this ob2b ecu pinout it dose look like connector C pin 1 black/white is for the primary o2 sensor heater circuit.

see if that is outputting 12 volts when the engine is first started

dcintron3790 · May 17, 2017

Thanks for the reply. I did erase the code after replacing the sensor. I will retest my voltages tomorrow to make sure I am or am not getting 12v to my Primary O2 Sensor. It does read the temp because I saw on my diagnostic app on my phone it read the that the sensor had not yet reached its functioning temperature. Once it reaches the temperature it goes into "closed loop, using o2 sensor for fuel mix" then goes into open loop system failure. I have also checked my PCM connector C pin 1, it was missing. No metal "clamp or housing" within the connector itself. And no black/white wire. I noticed this when trying to follow a diagnosis procedure for p0135 in the 99-01' Service Manual that is posted on here. I soldered a new wire to that pin and clipped the connector back into the PCM, and used the new wire to bring around front to the black/white output towards the o2 sensor. Not sure if thats the same wire. But I took a look at a circuit diagram for the PGM-FI and it looks to me that it goes straight from the PCM to the Sensor. Maybe I have that right and something else is wrong as well. It is a thinner wire than factory not sure if that matters.

dawg316 · May 17, 2017

hmmm let me know if that works out. also with the new pin that you installed on the ecu want to check and see if you got voltage coming out of it aswell?

dcintron3790 · May 18, 2017

So ive tested pin-1 correct voltage is coming out, also found another missing white which is for pin-16 which is a white wire that is a incoming signal for the o2 sensor. I soldered a new wire to pin-16 and pin-1, then I went around to the engine bay with the wires and connected pin-1 wire to blk/wht on the harness, and I connected pin-16 to the white wire on the harness. I could be having a bad connection as I am only able to tape the wire around the white incision I have made in the white and black/white wires, which could explain why my CEL is still on. But this time it flickers, and the battery light comes up on screen as well. Not sure if a bad or a good thing. I have a diagram showing me the circuit of the o2 sensor to the PCM and it shows the white wire has a split before going to the o2 sensor. I've also noticed a white wire in a loop in my harness which I am unsure if its the white wire I need for the sensor or a different one, but if its that one then its connected to something that it shouldnt be connected to which could possibly be the reason for the CEL still on and the battery indicator to show up as well.

dcintron3790 · May 18, 2017

I have tested pin-16 and voltage is coming out, at the required voltage.

dawg316 · May 18, 2017

heres where im not shure if i can help you, being a ULEV it runs a wide band o2 sensor and the pinout i provided above shows the pin 16 is o2 signal input into the ECU for a narrow band ( 0-1 volt oscilating wave) signal

you shouldnt of connected a pin to it and ran the wire TBH

the only code you had was for the heater circuit and not for the oxygen sensor. which would indicate a working sensor but a faulty heater circuit only.

a flashing CEL is never a good sign. also a battery light isnt either, but ithink those are just false lights beeing triggered.

remove what you did with pin 16.

leave the pin 1 heater circuit wire fix you did on tho. that repair seems correct

seb9316 · Oct 15, 2018

EDIT: I am getting the same P0135 code, but figured out it was in fact my 02 sensor and not the wiring harness as I first suspected. Sorry for the inconvenience