Hi Acurazine Followers,
I have a 2013 RDX All Wheel Drive that has a current permanent p3400 code, that failed CA smog, with 113,000 miles on her.

Back in 1/9/2025, I had an p3400 flashing fault code, my mechanic replaced the Variable Timing Control Unit, for bank 1. I also changed just because they were inexpensive, both pressure sending switches.The light reset & I assumed that the repair fixed the p3400 code, off I drove her until I needed my smog checked, 7,000 miles later. It didn't pass smog for my April registration, back to the mechanic.
The shop just checked the whole car out again, not finding any wrong, just the permanent p3400, that won't go away.
Mechanic thinks it is either a pcm issue or a piece of crap in the oil passages that feeds the variable timing control unit for bank one. It is not enough psi loss to trigger a p3400 flashing light, the pcm won't reset to clear the permanent fault code p3400.
Shop is a bit baffled about the code, not sure what to do next, other then putting a bomb to it.
Maybe I should sell it cheap and buy a new car? Or Throw some Seafoam in it, change the oil, drive it and see it it resets the code?
Loss in p3400 hell!,
Mark

 

If the DTC is permanent stuck and cannot be cleared via self-diagnostics, a scanner, and a hard reset (by disconnecting the battery), then replace the ECU. They are available Used on eBay for $30; have your mechanic link it to the immobilizer—that takes just 15 minutes of labor.

 

Ok which cpm do I pick? It has to be a 4wheel drive pcm correct?
Is my mechanic wrong about a pressure issue with resetting the pcm? What software and computer ie apple or pc does the mechanic need? Is a software upgrade available for the 2013 RDX?
Even if it has not flashed a cpm fault code, why replaced with a used pam?
Can I do this with a laptop and computer?

 

The most correct approach is to open the hood, remove the plastic cover, and take a photo of the part number itself so you can order an identical replacement.
You need a diagnostic scanner that features a function to link the ECU to the immobilizer. Every repair shop has a scanner like that.
First, resolve the emissions inspection issue, and *then* mess with the updates.
If it isn't displaying, then how exactly are you unable to pass the inspection?

 

I am not sure I understand, it isn't displaying, a flashing fault code p3400? The smog shop stated that the p3400 permanent fault code was not fixed with replacing the vcm control unit. Take it back to your mechanic, how them fix it right. I am not really clear what is going on, the mechanic is confusing me with an oil passage issue and not the pcm. But you seem to think that the pcm is an issue and not an oiling issue?

I guess I can force the shop to use my eBay purchase pcm and see it the permanent p3400 code goes away after a couple of hundred miles.
I just don't know enough about the variable timing on Acuras...

I have a scanner, but it just tells me what codes I have, and can only clear codes that just flashed.

 

I also don't understand why the Check Engine light isn't coming on—did you perform all the resets I listed above?
Try to find another mechanic who knows what he is doing.

 

I am not sure why the check engine light doesn't come on, all I know is the p3400 permanent code is still showing. The shop has not figured out what is wrong with the car. The only thing I know is they once again changed the rocker arm oil pressure switch on bank 1. Of course it didn't fix the problem, so I have the car now.

I will go out and find a plug and play PCM from a place in Oregon. They have done my Ducati reflashing of my ECUs. I'll have them check my current PCM, see if I bricked it. If I did, I'll get them to sell me a refurbished unit. At this point, I am done with leaving it a shop for months, only to have nothing done correctly.

 

What exactly did they do when reflashing the Ducati ECU? And how does this relate to the RDX ECU? Did those guys happen to mess with your original ECU? It is possible to programmatically delete the code mask—which prevents the "Check Engine" light from coming on—but the fault code itself will remain active. That is why I strongly recommend buying a used unit from eBay rather than messing around with refurbished ones.

 

No one has touched the RDX PCM, it has not been refurbished, it still has the factory program on it.

The reason I mentioned the Ducati, the program on the ECU which also has an immobilizer on it, sometimes gets corrupted and causes issues with the motorcycle starting, running correctly etc. You may have to reflash the the original ecu with a new program. Sometimes the original ecu can't be reflashed, which at that time you need to go out and buy a virgin ecu and have the program reflashed with the immobilizer deleted or installed. I am making an assumption, that you can also take that same Acura PCM/ECU, have a shop like the one that did my reprograming on my Ducati ECU, do the same with the Acura control unit. They check and see if the Acura PCM has a fault, or is damaged, they refurbish, reprogram and you plug and play the unit back into your car. If they can't repair your PCM, you buy a virgin unit, have them reprogram it like a Honda/Acura dealer would do.

I don't want to go to a dealer, or another shop to have a used PCM reprogramed with the vin of my car, which I understand that needs to be done with a used PCM. Or am I missing the point, you can't get a refurbished Acura PCM and use in the car, a used PCM is the best?
I have an idea that a used PCM could have the same issue I am having right now, it is later going to be corrupted or stop working correctly because of age and constant starting and shutting off sequences?

Did you have an issue with your PCM, how you fixed the problem was buy a used one?

 

New codes popped up after I disconnected the battery cable to reset PCM, in the AcuraLink. Electric Power Steering 85, Tire Pressure Monitor 85, Airbag System, All Wheel drive 41, and Vehicle Stability Assist 86.
The shop never told me about those codes, but I bet they deleted them.
Should I be concerned about them, is this stating that there is an issue with the PCM? Do I delete the messages or what?

 

Acura's self-diagnostic system is capable of storing error codes; this has no impact on vehicle operation—it simply means that no one has cleared the multimedia errors for a long time. The garage is not obligated to clear them, as they work via OBD-II and are not concerned with the Acura multimedia system.
As for ECUs: if they are selling for $30, that indicates that nobody needs them—precisely because of their extreme reliability. Consequently, attempting to refurbish a component that costs only $30 is about the most foolish thing one could possibly do.

 

Acura's Self-Diagnostis system has been reset by me every time, my car has thrown a fault code. As I said, I just disconnected the battery last night, I wanted to get in some drive cycles to see if the permanent p3400 code would go away. I have driven the car for about 7k m miles, since the control unit was replaced and it hasn't reset. I am no expert on the variable timing on this Acura, if the code is still there, can I be damaging my car, I drove the car for almost a year thinking the PCM reset?

As for the ECU/PCM, I would like to know why you are saying to spend the $30, have you experienced this issue, p3400 Cylinder Deactivation System Bank 1? Can I reprogram a used PCM with my laptop and purchase the iHAD software for one day? It around $65 for a one day license or $2,500 for 1 year.
Even tho the shop replaced the control valve, it has not reset, in your estimation, it is a problem with the PCM and nothing to do with an oiling issue?

 

Why is it even necessary to reprogram a used ECU? What is the benefit?
If you have a active code in your ECU, you are unable to pass a smog inspection because of it, and the "Check Engine" light is not on, then the problem is electronic—not oil-related.

 

On my motorcycle, I can't use a used ECU on another bike, without reprograming and matching it to the bike immobilizer. I am assuming that is the same with a used PCM from another car?

So I will be buying a used PCM for my car, it sounds too easy not to. I don't have to to anything special just plug and play or do I need a special scanner tool to rewrite the vin of my car and replace it on the used PCM?

Before I buy the used PCM, should I get the 37820-R8A-A54, or the new superseded unit of37820-R8A-A57?

Thx for helping me out with this!

 

You will need to register the ECU with the immobilizer; this can be done using any standard, budget-friendly ($500 range) Autel automotive scanner, or at any auto repair shop(10 minutes of job). Be sure to order the specific part number currently installed in your vehicle; if you opt for a new superseded ECU, you may have to visit a dealership to have it reprogrammed.

 

I decided to reset the computer, before I start changing out the PCM/ECU. I drove 15 warm up cycles with 200 or more miles. I just took it to another smog shop, which was able to pass the car. The permanent code p3400 is still being shown. But I will have two years, before I go thru the whole smog mess again.
The car doesn't go into Econo mode, right now the best gas milage I see is 23 mpg freeway/city. Before I was getting around 26-28 mpg freeway/city, when I didn't have the permanent fault code p3400 stored.
I told the smog shop owner about a year ago I had a mechanic replace the Spool Valve for bank 1, due to a permanent p3400 code. Two days after the part was replaced, I had the check engine light come on, p3400. The mechanic that replaced the spool valve told me that, said he fixed the issue, the check engine light never has come back on. He never told me the p3400 code never reset and was a permanent code still. Plus he just shared with me that a metal cap was found in the valve train area near the spool valve assembly. He just pushed it back into the valve assembly, that was newly replaced. Since the CEL never came back on, he assumed he fixed the car.
The smog shop owner said that the yellow check engine light may come back, because the last mechanic did not fix the problem. He said it still is a mechanical issue, not an ecu, which you would get fault codes for if it was. In rare situations, they may reprogram the ecu, but a Honda/Acura ecu don't normally fail.

I was going to try to fix it myself, but I found an independent Honda/Acura shop who can do the work. The new shop said that if the last shop replaced the spool valve assembly with an aftermarket Honda/Acura part, that is maybe why the metal cap popped out during operation of the car. The part was maybe assembled incorrectly and failed, which is why the PCM has not reset for over 7,000 miles of driving.

I will kept the group informed on what is going on with fixing the p3400 code...

 

This sounds scary.

 

Yet another proof that there is no point in speculating on forums and wasting other people's time if the mechanics involved are, from the very start, uncertified incompetents who have no idea what they are doing.

 

This variable timing stuff on my Acura, is something I never had to deal with. I assumed that my "Fired Mechanic" was being honest and truthful to me about my car & his ability to fix my car's smog issues. It seems all he did was replace parts hoping things would go the right way.
It really makes me mad that he took me for about $1000 to replace a part that most likely have to be replaced with a genuine Honda/Acura part. Plus I found out they broke a lot of plastic parts taking the car apart.
I guess it is a lesson learned, when it comes to working on American cars vs. European or Japanese cars, take it some one who specializes in! They worked on my 2000 GMC pickup to pass smog, which worked out great, not so much for my Acura...

 

I finally was able to pass smog. It seems in CA that after 15 start cycles and 200 miles, the smog shop can pass you, even with the permanent p3400 code.
The permanent code is still there, but I did take it to another shop to check it out.
The shop used two types of scanners, to check codes. One scanner, a handheld type like I have, showed the permanent p3400 code. The other scanner, a more expensive one, showed no codes, not even the permanent p3400. The shop owner checked everything with the high end scanner, my variable timing assembly unit was showing to operate correctly. The shop owner said he has not seen something like what is going on with this p3400 code, but the car is running too good and no CEL came on, so drive it like you stole it.
I have two more years until a smog check, I'll cross my fingers that it will pass again...