Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Hi, I have a 2000 Dodge Dakota 3.9L and I'm having issues I need to get resolved asap as it's keeping me from passing Ca smog which I need to register the truck. I'm getting two O2 sensor codes; p0138 and p0141. Both pertaining to my downstream heated O2 sensor. I've replaced the sensor, albeit with a non-OEM sensor and it didn't help at all. I used the "live data" mode of my OBDII reader and found that the voltage on that sensor was stuck on one volt, with no fluctuation at all. From what I understand from Scanner Danner's videos Chrysler uses an isolated power circuit for their O2 sensors meaning the power circuit is 100% isolated from the PCM. My factory service manual seems to bear this out. From, what I can tell the 12v path is as follows. Battery to Automatic Shutdown Relay to a 12 amp fuse. From there it splits into two, each one going to an O2 sensor and then out to a ground that is not in the PCM. Here's where it gets weird. With the key on, I applied my test-light to my fuses. All checked out fine except the O2 sensor fuse. It showed "ground" on each side of the fuse instead of power. I next put the test-light on the wire that heads from there to the sensors and sure enough, it too showed up as being a ground as opposed to a 12-volt power source. It left me totally scratching my head. I then visually inspected the ASD relay socket where I discovered something else that I can't explain. The socket that correlated to pin 87 was empty meaning there was no metal for it to make contact with at all. I always thought that pin 87 fed to whatever accessories needed to be powered after the switch in the relay was thrown? So it seems I have a relay socket/wiring issue, right? But then it occurred to me... "What about all the other things controlled by the ASD relay? Like the fuel pump, fuel injectors etc? How can they all still be working? So I'm completely stumped. Can anyone shed any light on any of this? I'm thinking there's something obvious I must just be missing. Any help would be greatly appreciated so I thank you in advance as I really need to get this resolved right away. Not just to get my registration current but for my piece of mind as well. It's already taken a year or two off my life expectancy. Thanks again, Tom
ASD doesn't stay on KOEO. It'll usually come on for a couple seconds when the key is first turned to run then goes off and doesn't get turned back on until the engine is cranked. And like you said if there was a problem with the ASD the engine wouldn't run.
Since both codes are set by high O2 signal voltage I'd forget about the heater and check voltage on the signal.
I wouldn't dismiss the heater circuit, just yet. Chrylser uses a 5 volt bias on the O2 signals. Until the sensors heat up, voltage will be high.
But, as Matt T stated, ASD will only remain energized for a few seconds, after the key is turned on, unless there is a crank signal.
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
This may be an old wives tale, but I have owned Chrysler and Mitsubishi vehicles for years. Be careful using generic O2 sensors in these vehicles. That has given ME grief more than once. I have had good success with Bosch or OEM from the dealer.
...Jim
Last edit: 3 years 4 months ago by J.D.. Reason: spelling
