Code P0154

[Homeoboxter]

Dear Community,

I`m having this code P0154 coming up every now and then, which indicates a discontinuity issue between the O2 sensor and ECU. What does typically cause this? Is there a connector that usually fails and I should look at? Or it`s more likely that the sensor itself is dying and I should just go ahead and replace it?

Thanks for any input!

[Stl-986]

1st thing to do is check the connector & the wiring. Wouldn't hurt by spraying some electric cleaner on the body side of the connector (not on the o2 wiring side), clear the code and see if it comes back. If it does and you have checked the wiring continuity back to the DME then it's time for a new o2 sensor.

[Homeoboxter]

Thanks. After clearing the code, usually it comes back in a day or two. Today it just came on while idling at the red light, so I think it`s unlikely that it`s some connection issue because then it would come on when hitting a speed bump or such. I`ll check the connectors just in case.

[Stl-986]

cars vibrate...it can still be the connection. Until you get under the car you dont know if it is even plugged in all the way. Double check it & clean it first...it's free, then check wiring...again free and if all that is good then replace.

[blue62]

You could use a Digital Multi Meter and back probe the first connection from the sensor.
Back probe the Sensor side of the connection. get the Sensor up to operating temp. and see if you get a voltage signal. if not the sensor is toast. If you get a voltage signal then you have a wiring issue.
I believe these O2 sensors are four wire. look for two wires that are the same color, usually white but not always. They are the heater circuit. probe the other two they are the signal wires. Polarity doesn't matter.

[Homeoboxter]

Originally Posted by blue62

You could use a Digital Multi Meter and back probe the first connection from the sensor.
Back probe the Sensor side of the connection. get the Sensor up to operating temp. and see if you get a voltage signal. if not the sensor is toast. If you get a voltage signal then you have a wiring issue.
I believe these O2 sensors are four wire. look for two wires that are the same color, usually white but not always. They are the heater circuit. probe the other two they are the signal wires. Polarity doesn't matter.

Excellent information! But shouldn`t it trigger CEL right after I erase the code if it`s toast? CEL comes back usually in a day or two.

[JFP in PA]

Originally Posted by Homeoboxter

Excellent information! But shouldn`t it trigger CEL right after I erase the code if it`s toast? CEL comes back usually in a day or two.

No, hard codes are only triggered after certain parameters (# of times repeated, number of miles, etc.) are met; until then it remains "pending" and the check engine light stays off.

[blue62]

Originally Posted by Homeoboxter

Excellent information! But shouldn`t it trigger CEL right after I erase the code if it`s toast? CEL comes back usually in a day or two.

CEL could be from a faulty connection, faulty wiring, or a failed O2 sensor.
I you back probe with a DMM the way I described you will know if it is the O2 sensor or the wiring.
And you will know with the least amount of work.

Back probing can be a little fiddly sometimes but I feel it is the best place to start for your issue.

Remember you want find the connection closest to the O2 sensor and back probe the O2 side of the connection. Not the harness side.
your O2 sensor should be a four wire.
It will have two wires that are the same color. Those are the heating circuit.
You want to back probe the other two wires.
Polarity doesn't matter.
Then you have to run the engine for a few minutes to make sure the O2 sensor is heated up. They have to be around 600-650 degrees F before they start to function.
If you have a OBDII scanner hook it up and watch the other O2 sensor for when it starts working- goes into closed loop. Then you will know things are heated up.
If the suspect O2 sensor is working it should show a rising and falling voltage between I think it is .2 -.95 millivolts.

If you get a voltage signal from the suspect O2 sensor when you back probe it as described then you have a wiring issue. If you don't get a voltage signal from the Sensor it is toast

Hope this helps in some way.

Oh to answer your question:
Some Codes have to happen twice back to back over two drive cycles before they trigger the CEL.
The first occurrence they are set in an area of ECU memory called pending codes. Second occurrence moves the code to permanent code memory and triggers the CEL.
Most issues which are not immediately harmful to the cats are handled this way.
A misfire which can harm the cats sets the CEL on the first occurrence.
That's my current understanding of how it works.
**************** could change tomorrow LOL

[Homeoboxter]

Fantastic, I`ve been enlightened! I`ll try troubleshooting this with my multimeter once I get to it perhaps in the weekend. Thanks Guys for all the input!

[blue62]

Originally Posted by Homeoboxter

Fantastic, I`ve been enlightened! I`ll try troubleshooting this with my multimeter once I get to it perhaps in the weekend. Thanks Guys for all the input!

Let us know how you go
Once you figure back probing out it is something you can us the rest of your days.
Watch some youtube vids like Scanner Danner he is always doing it.