PCM replacement misdiagnosis?

Hey yall,

First time poster, been lurking for a while.

I bought a 2020 SR about a month ago and I absolutely love it. A week ago it started throwing a P2716 code (Pressure Control Solenoid "D" Electrical) and I took it to a shop to get it diagnosed. They told me that everything in the transmission looked good, no wiring issues, but that I needed to replace the solenoid and that would solve the problem. I went ahead with the repair (they changed the ATF fluid and filter as well) and about five minutes after driving it off the lot, the check engine light came back on.

I thought maybe it just needed a drive cycle to reset but wanted to make sure that everything was okay so I brought it back. They told me that I needed to replace the PCM which seemed fishy to me because based on the research I've done it seems like I would be experiencing noticeable driveability issues if that was the case. It drives fine and felt totally normal both before and after the repair. It's not in limp mode and isn't shifting funny or running rough.

I don't really trust their diagnosis at this point and declined the PCM replacement. When I picked it up, the check engine light was gone and I haven't driven it much since then (a few miles up the road and 3 key starts to see if it would resurface) but it hasn't come back on yet.

Kinda feel like they're trying to pull one over on me because they assume that as a woman I don't know anything about cars. Admittedly I don't know all that much about the electronic side of vehicles, although I have years of experience repairing guitars and amps, so I'm not completely ignorant when it comes to an electrical circuit. I've also done a whole lot of (mostly non-electrical, other than fixing a short in my stereo) work on my '99 Tracker over the years.

I've made an appointment with a Toyota dealership but it isn't until Wednesday. I drive this truck for work and want to know if yall think it is safe to drive until then. What is the likelihood that I actually need to replace the PCM? Are they just trying to get an easy $1000 out of me? What would you do in this situation?

Thanks guys!

 

certain components are covered under an extended timeframe, emission components which a pcm may be covered under.
like any part related to CEL in certain vehicles are covered 8 years / 80k miles, etc...
Dont quote me on the #s, its afford thing, some are even higher, some lower...
Costly emissions related stuff have extended coverage, would imagine toyota also....
Might be worth going to your local dealer, or making a call to a writer with your VIN & ask if your pcm is still covered under emissions warranty.
Cry once, pay once, take it to the dealer & get it diagnosed correctly....

Sounds like your shop has no clue.

 

Need to drive it & get the light to come back on or the visit to the dealer will be a waste of time & money.
That light coming back on is key, thats where all this info is....

 

Thanks for the response! I'm at 110k so unfortunately think I'm past the warranty coverage but I'll do some driving this weekend to see if it comes back on. If it doesn't I suppose I'll cancel that appointment and make a new one if it comes back later. Appreciate you man!

 

Welcome to TW..

 

Also promptly after you figure things out badger your shade tree boys for a refund for the mis-diag, threaten youre going to call & file a complaint with the BAR, Bureau of Automotive Repair, bla bla bla....
They will give you lip service & say the part was needed, call the BAR....

Thats only if you have a backup plan in your town...

 

Unfortunately you're probably right. unless its unlimited miles...
But a quick search on the web, AI states 8 / 80....
so youre over on mileage.
PCM failures aren't that common in todays world.

Could be something as stupid as the cheap part they put in is garbage, assuming they went cheap...

 

I already gave the owner an earful and laughed in his face when he referred to ohms as "O H Ms" like it was an acronym. He also tried to correct me and tell me that it was an "ECM issue, not a PCM issue" which I told the mechanic and he said "yeah the owner isn't very knowledgeable about these things.." Like yeah buddy I noticed!

 

E or P, end of the day, its the same thing....
Not trying to get personal, where are you located?
Only reason I ask, some regions have more techs faking it than others....

 

I know, that's why it irked me when he corrected it! You'd think the owner of a transmission shop would know that..

 

Located in Nashville TN. I've got a regular mechanic that does great work and I trust him completely, I brought all of my fleet vehicles to him for years and he's a straight shooter but he doesn't do transmission related codes so I went to this shop on a recommendation from someone else.

 

>95% when you have a circuit code for an output (the shift solenoid in this case) it's a wiring issue or the component is bad, it's rarely the ECM/PCM

So many shops/techs/people go directly to replacing the component though instead of doing any testing or inspecting of the component or wiring, then when replacing the component doesn't fix it they go to "well it must be the ECM". When that doesn't fix it "well you need a whole new harness".

Finding a shop/dealer/tech that will put in the time to do proper testing is really becoming the exception rather than the norm anymore unfortunately.

 

Hi there -

My comments for your reading pleasure, starting with a summary as I read it and then a recommendation.

Summary:
You bought a 2020 Tacoma. Unfortunately, shortly thereafter, it threw an unusual transmission code. You had it serviced but the CEL returned almost immediately. So you took the truck back and said (paraphrasing here) "this is not an acceptable outcome, fix it". Way to go.

Thankfully, at the end of the day, you got your truck back and it has been running fine since then. No more CEL(s). It is possible there was a glitch and maybe your tranny burped a little with the new fluid and filter and solenoid or something and it just threw a CEL until it settled down after the new fluid had circulated and the filter became saturated Not the greatest of technical assertions I admit, but I've seen crazier.

The most important thing for now is that you are operating and driving normally. I completely understand a mild sense of ongoing apprehension. The longer you go, the more that will go away.

Yes, it is possible that shop was somehow trying to pull the wool over your eyes by faking a CEL light to come on. It is not that difficult. Nick a wire somewhere that is impossible to find (except for them). That's dirty poker if so. It is also a pretty serious allegation to make without evidence.

Recommendations:
* I would give the shop the benefit of the doubt. But I would also be inclined to avoid them in the future. Just ignore them.

* Keep up the confidence and questioning attitude in the future. Love it! It is A-OK to say "I don't understand how that can be" or "I think I want a 2nd opinion" or even "I believe I deserve my money back". More power to you and everyone else.

* Should, and I hope not, you ever need need a PCM understand the following:

1) PCM failures are indeed rare. Especially in mild climates like Tennessee.

2) PCM failure diagnosis is not an exact science. It is usually a combination of very unusual issues, inability to communicate with modules or an OBD-II reader, the Christmas tree of lights on the dash and that type of thing. Anyone who tells you a new PCM is required darn sure better be able to explain *why*. Demand a copy of the wiring diagram they used and the notes they took and circuits they tested. Seriously.

3) In today's world, it is far better - and I mean this is not even debatable - to send your PCM off to be repaired / reprogrammed / restored. This is a booming cottage industry. Companies like UpFix and FlagshipOne are doing this every day all day. The best part is you will get your own PCM back and it will literally be a plug-n-play. No messy VIN matching, no messy odometer mismatches, etc...

HTH & best wishes!

Andy

 

I really appreciate the detailed response, thank you so much!

To be clear I don't think they faked the CEL, I just don't believe their assertion that it calls for a new PCM. When I asked them how they came to that conclusion they told me a whole lot of nothing. Also, when I called the dealership to tell them about the situation and make an appointment, they told me it was totally possible that it was just that the truck needed a drive cycle to completely clear the code after the solenoid replacement, so I'm holding onto that hope since it hasn't come back. Fingers crossed that it doesn't!

Also that's great to hear about the send off repair alternative to replacement if it does come down to that. Yesterday I looked up a few different companies that do that and they had good reviews, but since I don't know anyone personally who has had to do that I wasn't sure if it was actually a viable option or which one to go with. If you have any recs for a company you trust please let me know!

Thank you so much for taking the time to reply. Yall are awesome!

 

Thanks!

I've never personally used one myself. But I can tell you this is a known best practice in the Ford Mustang and Jeep Wrangler world. Which is a huge number of vehicles out there. Millions.

Stellantis - parent company of Jeep, Dodge, Ram, Chrysler - is notorious for PCM and TIPM (totally integrated power module - aka the underhood fuse box) failures. Ditto for Chargers and Challengers and Durangos.

In the Ford Mustang world, there was an entire generation of Mustangs that were notorious for BCM failures (body control module - aka "smart junction box" aka interior fuse panel) that would get wet from rain leaking down the A-pillar. The moisture and corrosion would fry the BCM and create all kinds of havoc with the radio, locks, windows, HVAC, dash cluster and more. Also, in the Mustang world, especially with the 5.0 Coyote engine, you have a whole subset of people who try to make modifications to the PCM (aka "tuning") for nonsensical things like a cold air intake and cat back exhaust and what not. And they wind up corrupting or bricking their PCM. Some of these same issues carried over to the F150 world, but to a far lesser degree.
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I have a Jeep Wrangler that has been modded with a mild lift and lights and a kick a$$ stereo. And very well-maintained. So I know about issues with the TIPM through a sister forum like this. Just never experienced it myself. Wiring diagrams and wiring things don't scare me, I guess you could say.

Likewise, I had a ridiculous 2011 5.0 Coyote Mustang that was supercharged and had a tubular suspension and more. Never had an issue - either did it myself or had a pro do it - but I sure knew about issues that many others experienced. Again from similar sister forums. I was fortunate and able to keep that vehicle garaged its entire life too before I sold it.

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UpFix and FlagshipOne - based on my research and reading - would be the first ones I would call.

 

Welp, drove it about 40 miles yesterday. No check engine light, everything felt like it should, shifting fine, normal RPMs and gas mileage. Today, I took it a few miles up the street and the CEL came back on. The dash screen above the steering wheel and the airbag light started flickering a little, but not the main infotainment screen. Took it back home and it still drove normally the whole way.

Definitely electrical but now I'm wondering if it really is just damaged wiring. We do have a lot of squirrels terrorizing our neighborhood.. Thoughts?

I got a recommendation from a friend for a locally owned shop that specializes in Toyotas so I'm going to see if they have any availability to take a look before the dealership appointment I have scheduled. I don't really want to take it to the dealer but since this is my work truck I do need to get it figured out as soon as I can. I'll just have to see how soon the other shop can get me in!

 

A lot of the time with electronics the issue isn't with what's broken, it's with what broke it, I'd check for shorts.

 

That would make sense. I'll make sure the next place I take it actually checks thoroughly. I just feel like jumping right to the PCM seemed like the nuclear option, and y'all have made me feel a lot better about questioning that diagnosis. I really appreciate you guys!

 

Intermittent trouble codes (flickering CELs) are almost always a wiring problem. More specifically, where a 12V wire has chaffed through its outer sheathing and is occasionally now touching metal - such as when the chassis flexes. Or you have a loose harness connector with moisture in it. That type of thing. Anything that momentarily interrupts the 12V circuit. This occasional short to ground is what causes the issue.

Unfortunately, these can be a challenge to find and locate.

I would re-check for DTCs. You may (should) have a stored DTC even if it is flickering or intermittent.

Rodent damage is a very very very real possibility. Especially if you park near a tree, field, barn, farm, or where firewood is stored, or where food is kept (deer corn, dog kibble) etc... in your garage or car port.

The DTC could at least help you narrow down which circuits to be examining.

 

I think you're absolutely right! Just read that code again, it's still throwing the same one as before the solenoid repair (P2716). I don't have a garage at my house and I'm pretty sure my senile neighbor feeds the squirrels, so I wouldn't be real surprised if one of them has been wreaking havoc on my truck guts. Is there a diagram out there that might help me get a general idea of where to look for that damage?