i have a 2004 ram 2wd 3.7 and i cant get the O2 and catalyst monitors to ready status. the truck failed inspection for O2 sensor, i changed both after cat sensors. 4,000 miles later, the monitors still wont clear. went to dealer and they updated the computer, but that did nothing. now there telling me i need a new pcm. i have 3 days before my registration expires and i cant renew until the truck passes inspection. is there anything else i can check before i dump money into buying the pcm? any help would be appreciated. this has been going on for months.

 

It's isn't your post cat sensor causing you grief.. its the upwind... Make certain and get the right one.. I rec ngksparkplugs.com, or something to that effect.. drill down and find a good ntk by ngk..

 

https://dodgeforum.com/forum/dodge-r...s-section.html

 

The code that originally came up was for the after cat sensors. Do u think I should go ahead and change the other 2 before I start messing with the PCM? I guess it can't hurt since the whole monitor problem started after I changed the other 2 sensors.

 

Change all of the O2 sensors, clean the MAF Sensor (WITH MAF SENSOR CLEANER ONLY!), Clean the Throttle Body (WITH Throttle Body Cleaner) then reset the PCM... see if you get different results.

When you don't pass inspection they are suppose to give you a failure report so you can see what the problem is.

Usually when you don't pass the readiness test it is because there is something wrong elsewhere that is preventing it.

There can be a million different things wrong, and replacing the PCM is usually the last resort...

Is your truck modified in any way, shape, or form?

 

your PCM indicates to me, at least, that it is doing it's job by telling you 'not ready'....

do you have a programmer or scanner you are using to clear or observe codes? If so, every single time you use it, it resets the DTC codes to baseline... which means it will take time to build the data back up.. it generally takes 50 miles for catalyst to 'ready', around 70 or so for o2 sensor(s) to ready, and another 20 or so, plus additional key cycles, for 'o2 heater circuit' to ready.. It may take up to 150~200 miles for EVAC to 'ready'.. this is just how it goes, unfortunately..

your upwind o2 sensors carry the brunt of the load when it comes to information to the PCM.. regardless of what many think, the downwind sensor plays a role in a/f trim too- albeit a much smaller role- BUT- it's primary purpose is to tattle on the catalytic converter if it is misbehaving..

is your truck cali emissions or 49 state? cali rigs require a different o2 sensor, and the downwind sensor on cali trucks is a four wire, which indicates it provides more data to the PCM than 49 state trucks are programmed to do..

I would highly rec you replace the sensors.. every one of them.. find NGK/NTK's webpage and drill down into the database to find your specific year and model, and cali emissions or not.. o2 sensors are fairly fragile.. the filament inside them can be damaged easily by dropping them.. add to that, there are tiny passages that sample exterior air- most folks don't know that.. the o2 reading is derived from tiny voltage differences between the exterior reading and the interior reading.. the filament that dangles inside the guarded shroud on the interior probe runs through the center of the sensor (which is heavily insulated) and to just under the exterior vents.. the vents are just tiny holes that perforate the casing, and run around the circumference of the surface where teh wire comes out.. again, the voltage is measured in the center, and under where all that insulation/ceramic/heavy metal is (where it kinda 'bulbs')..

some of the things that will absolutely wreck a sensor is dropping one and damaging the filament- which isn't that common.. what is common that will damage it quick like are oils (not too bad, but possible), grease (clogs them, it isn't necessarily the chemical reaction), and coolant.. coolant is the BAD one.. coolant will render an o2 sensor useless in quick order- which prompts me to ask: do you have a leaking heater core? or, do you have a freeze plug that is leaking? just a little coolant, and that bad bear is toast..

my personal opinion is that TB and TB sensor cleaning isn't going to help you pass inspection, but it will help you run better..



now, you didn't hear this from me.... it is too controversial... but... back to those tiny vents on the OUTSIDE of the sensor- you can block them, and make a functional o2 sensor believe the catalytic converter is operating at peak.. the same thing can be done more effectively using the non-fouler trick.. all that said, I still rec you swap all your o2 sensors...

 

^^ Nice info there.

Just FYI to the OP - when you turn the key to the ACC postion and the MIL goes to a steady position after a few seconds it means the monitors are in a readiness state. If it continues to blink then it indicate the i/m sensors are not ready. Helps when preparing for emissions.

 

The truck only has 40k miles and is not modified in any way. I drove thousands of miles between checking with the scanner. It originally failed for an after cat sensor code. I changed both after cat and thats when I ran into the monitor problem. The sensors went right from the box into the truck, never dropped. No engine leaks, no other problems. I think I'm gonna buy the other 2 sensors today n try that. I did see that the truck has its own readiness test n I try to check it all the time. Light always starts flashing. Oh, and I'm in NY. I'll post back and let u know if the sensors worked. Thanks for putting in the time to post back. It's greatly appreciated.

 

what brand o2 sensor(s) did you use?

another controversial conversation, but: Bosch and Dodge don't seem to like each other.. it has something to do with the latency of signal leaving that thing (the speed and/or delay it reports back).. for that reason, most try to use only NTK/NGK, or Densco sensors.. they don't seem to fart so much.. that, all by itself, may be your issue..

 

Denso is your best bet for sensor brand.. the Bosche has slightly different resistance than the OEM and Denso sensors so it heats up a little slower, and Dodge's don't seem to like that very much...