Knowing 4 sure if PCM is bad

My 05 Acura TSX went into limp mode outta nowhere a few mts ago. The DTC it throws is U0107…lost communication with TAC module. I found a flow chart in the service manual for diagnosing this code which mainly had me test the wiring for continuity and voltages…all which showed as normal. I got to a spot where it said to swap out the TAC module with a known good one, erase codes then retest for DTCs…well I replaced the module but it’s still got the DTC. I even went back thru the flow chart and redid all the steps…even the ones in between (for example it’d say something like test pin 20 on PCM connector B and TAC relay prong 3 for continuity…if yes go to step 12 if no go to step 14…rather than going to 14 I just did did EVERY step) and everything shows as normal. There is also a place in the chart that says to swap in a known good PCM which I was also led to but of course I’ve been unable to do that. From everything I’ve learned it appears to me the only thing left that could be causing this is a bad PCM, but I’m new to all this so that’s why I wanted to ask if anyone knows anything else that could be causing this problem. It’s the only DTC btw but before this happened my car had started having an issue with what I think is called the shift lock solenoid…it refuses to go out of park unless I manually override it by putting the key in the hole near the gear selector and put it in neutral before cranking. The PCM controls this as well but of course it could be totally unrelated. I just thought it was mentioning. I’ve charged the battery up to 13v several times so it’s got enough voltage.
I haven’t been able to remove the PCM to open it up and visually inspect the board bc one of the connectors is stuck and I haven’t been able to get it out which is so frustrating!! I’m almost wondering if the dealership super glued it in bc less than a mt b4 this started the car was taken in for a recall on corroded PCMs where they put a cheap thin piece of plastic on top of it(that wouldn’t help prevent corrosion) but I wouldn’t put it past those crooks to switch my PCM with one that was going out or do something to mess mine up thinking I’d be forced to come back and pay out the a$$ for repairs…esp if they super glued one of the harnesses! I hope I’m just being paranoid there but it makes no sense how all the rest of the harnesses came out fine and I’ve spent hours trying to pull that one out even sprayed wd40 and it won’t budge!

Anyway, any input is greatly appreciated!! Thx!

A good independant mechanic will probably find the problem in no time and It will save you a lot of headaches.

Many times diagnosis of a bad PCM is to eliminate all other possibilities. On most occasions when doing this, the PCM is replaced because there was a mistake made on the process of elimination, causing an unnecessary PCM replacement. Bad grounds in the circuit is a common oversight. Proper reference voltage can be missed. There are multiple sensors for the TAC that should also be checked. Some also need reprogrammed after replacement. A competent mechanic with a scan tool can help make a more thorough diagnosis.

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I’m just now seeing the responses. I know that there’s an APP sensor…or 2 actually…and a throttle position sensor, all of which tested good. Also shortly after writing my question I ended up removing the drivers side paneling that revealed the other side of the PCM. The drivers side edge of the PCM is covered with corrosion! I realized also l that the dealership didn’t follow instructions properly when performing the PCM corrosion recall bc the cover shld have been bolted down with the bolts that hold the PCM in place but that was not done. I’ve been trying to get the PCM removed so I can open it up and see if the corrosion is on the PCB but can’t seem to get the bolts to budge! Are there any other sensors I’ve missed? I’ve also tested the PCM ground circuits and they test good under continuity test. I had already heard that the PCM is usually only decided as the culprit by process of elimination…after checking everything else…so yea that’s why im trying to know whether I’ve checked evrytng else. I cannot afford to take the car to a shop, that’s why im doing everything myself. I’ve cleared codes multiple times but it keeps coming back.

The U0107 is a Loss of comms with the throttle actuator control. IF the vehicle does not have what it sees as full communication with and control OF your throttle… it will not allow you to move the gear selector on purpose…as it does not know where the throttle position actually is. You can understand how something like that might be “problematic”

The U code also suggests that there is something wrong with the Circuit itself. Since you seem brave enough and have been messing around trying to figure this out… You need to do a Pinout from the PCM connector…thru to the TAC connector. Make sure all wires have continuity and none are shorted to ground.

That’s what I’d be doin…

P.S The Acura enthusiast sites are an excellent place to gather info and attempt to solve this issue…they may have seen this before and might be able to speed up your progress greatly. They are especially good with having ECU Pinouts as well… Dont overlook this resource


Thank you for your quick response!! I mentioned in my very first message on this forum that I had done all steps in the flow chart for this particular DTC which included continuity& voltage testing at the PCM & TAC
module (as well as TAC module relay) and everything had continuity, the voltages were normal and the ground circuits tested good…the only thing that didn’t test as expected was the +B circuit in the TAC module…the instructions in the flow chart asked if there was battery voltage for a couple seconds after turning the key to “on” position…it says to connect the positive lead to the +B pin in the TAC module harness (green with yellow wire) and the other lead to ground. It does show battery voltage but instead of only a couple seconds it keeps showing battery voltage as long as the key is on. Do you know what would cause that?

My apologies… I didn’t fully realize how well you diagnosed this issue. I’m used to advising what you would call…“beginners” so… my bad.

Ok… the only subsystem circuit that I know of in Honda Products that will power on for a couple seconds and then shut off is the PGM/Fi relay circuit… it supplies voltage to the fuel pump for the “prime” feature and then waits for a tach signal before flowing constant 12vdc to the pump.

Perhaps the PGM/Fi or similar relay in this Acura also supplies power to all the engine sensors at the same time…just to get a health check while it primes the fuel pump. It would be an ideal time to do this.

Now…I keep saying PGM/Fi…because back in the day that would be the fuel pump prime relay…but maybe just maybe there is an 05’ equivalent relay that does the same thing…but not named pgm/fi relay anymore maybe? Maybe it is because like I said…while priming the fuel pump for 2 secs…it would also be a great opportunity to poll all engine sensors at the same time… Thats just a thought…mite be totally wrong about that.

If I owned your vehicle I’d have better info for you. I tend to study up on the vehicles that I have… I will ask a couple buddies of mine from my “Honda Days” …engine swapping Honda and having all sorts of fun. Maybe they have a nugget of info for me. Stay tuned.

i got lucky and came back to this forum by just coming across it in Google search …I wasn’t expecting to see a response. There’s obv something wrong with my account set up bc I never see emails telling me about responses.

Anyway, yes I’ve been dealing with this mess for months and within that time I’ve gone from knowing nothing whatsoever about vehicles (& very little about electronics) to…well I’m no expert by any means but I’ve surprised myself by just how much I’ve learned in a relatively short time.
Anyway, yes I’m def beyond the beginner level stuff. The U0107 DTC manufacturer troubleshooting pretty much sticks to all the testing being done right between the TAC module subharness and PCM but after doing all that multiple times I decided to just go ahead and test the sensor wiring as well & all that was good as well. I might have been incorrect about the B+ circuit in TAC module harness only being supposed to have power for a second or 2…it doesn’t say whether it shld or shouldn’t in the instructions…it just asks if the circuit has battery voltage for a couple seconds then whatever answer you pick leads you to different steps…I just did EVERY step there was. Lol

Since I last wrote on here I’ve gotten the PCM removed and eventually managed to get to the PCB inside (the screws were so corroded…esp on one corner that the screws stripped…one that holds the top cover & another that held the PCB inside the housing…I ended up having to drill thru the screw to get the PCB out!! Anyway, the board was covered in corrosion & one of the chips was so badly corroded that one of its legs had completely disintegrated! Here’s a picture

Flood car?
I’ve seen damage to IC leads like that on fielded boards after 6 months to a year if the flux is not properly cleaned off esp prior to conformal coating. But the sum total corrosion looks like the result of being flooded at some point.


Awww man… now you went n done it… opened her up

The Blackbird is not in his natural environment when staring at those green boards of mystery, physics and science. I can spot burnt objects, cold solder jernts but not much further…

See… if it doesnt actually “move” then my primordial reptilian cerebra cortex basically just looks back at me and shrugs. If it moves, i have near instant comprehension… no move? No Bueno.

Someone once told me that there were these imaginary things called electrons that flowed thru and moved within that voodoo box you have opened… a novel concept to tell the young uns i suppose. Next you guys will tell me these magical electron pixies are actually man made by rotating a coil of wire within a magnetic field… you people come up with the most creative fairy tales.

Where’s my erector set with the crane? I fully understood that thing at 4 yrs old…im gonna pull that out and set it up again to really give it what fer right n proper. Because, it moves, you see.

Blackbird out


Made me think of this one, for those challenged by stuff that moves:



Well the reason for the corrosion is actually due to (well several things that worked together) but mainly the location of the PCM being near the center console floor & in contact with the floor board carpet. There was a recall on my PCM for corrosion which said that the salts used for de-icing the roads can come in contact with the ECM from the floor carpeting and eventually corrode the module. The worst part about my case is that I had just gotten this car back from my brother (who “borrowed” it for years) & never bothered taking it in for either recall. So when I got it back I took it to the dealership and had the recalls performed (supposedly) then literally less than 100 miles later my car went into limp mode out of nowhere!
I didn’t have the money to pay for diagnostics so I did plenty of research. (Like I’ve mentioned before I already had a fairly decent understanding of electronics but not relating to cars). I found the service manual which has wiring diagrams and instructions for diagnosing trouble codes. I followed the instructions and all of the voltages and resistances were normal. It took me to a point that said to replace the TAC module so I did that but still constant limp mode. The testing had me taking voltages from the PCM harnesses but they are all on the passenger side. I did notice when first removing the passenger side trim to get to the PCM harnesses that the plastic piece that was supposed to be a cover for the PCM wasn’t even on the PCM but instead just practically thrown into the spot where the PCM and a couple other modules are located.

Later once I decided to start taking more trim out (just to trace a lil more wiring bc I didn’t know what else to do) the first piece of trim I pulled out revealed this:

After seeing that I was extremely mad at Acura bc I was sure that amount of corrosion didn’t just build up over 5 weeks (of dry weather while my car was in the garage). So I decided to search for the recall info and found this:

After reading that I realized that the cover should have been bolted down WITH the PCM. The tape they put on wasn’t even on the right edge! But the instructions also say that if corrosion is visibly present to hook the car to a scan tool and the only way they should replace the PCM is if there was one particular DTC!! So (besides the fact that they didn’t put the cover on like they should have & didn’t clean the PCM housing) they followed instructions as far as not replacing the unit!!
I bought the car in 2011 and stupidly put it in my brothers name bc id planned to file bankruptcy and was under the impression that I’d be forced to sell it and get a cheaper car…plus I trusted my brother. (I learned that was a mistake when he asked to “borrow” it 4 mts later and never gave it back until last year with bald tires, bald brakes, bad battery, completely shot rack and pinion & needing regular maintenance items!!) But the point in telling you that is…I know 100% the car was never flooded.

Did you have the one with the electromagnet at the end of the boom?


Just out of curiosity . . .

How would you have reacted if the guys at the dealership had said this . . .

“We performed the recall and determined that your pcm is indeed corroded. However, you don’t have the appropriate fault code, which would have allowed us to replace the pcm at no cost to you. Would you like us to prepare an estimate to repair the vehicle at your cost?” . . . ?!

Would you have said “Go for it. Here’s my credit card information.” . . . ?!

Would you have said “I’m not going for it. Let me have my car back.” . . . ?!

Or something else entirely . . . ?!

I’ve seen these situations happen, and usually the only way the customer leaves there satisfied is if the service manager gets involved

My response would have been that I am only willing to pay these charges if replacing the PCM actually solves the problem, and not if it is a misdiagnosis or trial-and-error attempt to solve the problem. I would tell him that I need it in writing that if the PCM solves the problem, then I agree to pay the $X, however if it does not, then I will pay no more than the wholesale price of the part and no labor or markup.

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Im not sure what you mean about the electromagnet at the end of the boom?
There was never any “boom” sound…only car not accelerating normally.

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If the dealership had said that to me AND I knew then what I know now I’d most likely say something along these lines: " I need to speak to the head of management for this location" then tell that person that its completely absurd for Acura to handle a recall in such a way, as in “pretending” to fix the prob when in actuality all their doing is taking the cheapest way possible to fool people into thinking they’re providing a fix…The same thing they did with their pwr steering recall, acting like it was the HOSE rather than the rack and pinion. Then I’d say that I expect my PCM REPLACED immediately at no charge or else I’ll make sure to tell the Main CEO at Acura that the class action suit I’m about to bring against them is all thanks to you. Then I’d say im sure they won’t mind paying out millions rather than the price of one ECM, and allow you to keep your job. Somewhere in there I’d also throw in how it won’t be hard to prove that corrosion on electronic components can cause any number of faults, not just one.

I’m seriously POd about this if you guys can’t tell!

The dealer and the technician were paid by Acura to perform the recall as per the instructions. You should have towed the vehicle back to the dealer when you discovered the corrosion and asked them to perform the recall properly before you report their failure to perform the recall correctly to the manufacture.

It was in reference to the erector set that Honda said he used as a kid. I never had one but evidently some had a magnet at the end of the crane.

Reading with interest but you’re way over my head. I would just suspect though if the PCM is corroded, that would be the likely problem. Are you able to renew the board?

NO dernit… I dont have that model @old_mopar_guy … I wish I did tho. I had to get by using earth magnets and also an Ice tong type device that I made after seeing how car batteries and large ice blocks were carried…by that offset handle pliers type claw, which I’m sure you know about. I did have electromagnet envy for a long time afterward however, but I’m fully recovered now!

BTW @moneymaker8484_158151 the comment about the electromagnet and the “Boom” was for me…not you (reference the @who located within the comments…you can see who is being directly asked or referenced).

Disregard…it was just me up to my usual behavior of steering these many threads into the weeds as I am wont to do…often. Just having a little fun. If you want to know what he was referencing…look up in the thread about me talking about electricity and things that move…having a little laugh.