P0657-Bad ECM?

Let me start by saying I'm an idiot... While replacing my battery the other day I reversed the polarity for a second...The new battery had terminals opposite the factory battery and in my haste I didn't bother to check...

Initially it seemed that I just had blown fuses, the 120 A Alternator Fuse, 15A EFI and 30A ABS fuses. I replaced these and double checked the rest to be sure and they are all good. However on the second time I started the truck after replacing the fuses I got the CEL on and no responsivness from the accelerator pedal. Pedal goes almost to the floor before anything happens, and then the full range from 0 to redline is in that last inch and a half. Also the idle speed is messed up...usually its high, but sometimes low???

Got the code read and it is P0657- Actuator Supply Voltage Circuit/Open. Factory Service Manual says "replace ECM"

Couple questions-
First, the dealer said the ECM has to be programed with VIN #...does anyone know if the truck will run without doing this? From what I can tell the CEL will be on and theres a code for the VIN not being programmed, but I cant find anything that says if it will run.

Second, the truck runs fine if I disconnect the battery to clear the memory, however it only works for one trip then the CEL is back on and no acel pedal. Also I tried just clearing the code with a scan tool and that did not solve the problem, only disconnecting power to the ECM does. So whats the risk in just doing that in order to drive the truck until i get a new ECM?

Third, is it possible that the open circuit is anywhere but in the ECM? Ive checked all the connections as well as I can and cant find anything... Also too ECM out and there is no obvious damage.

I think I'm going to try and get a salvage ECM, but I need to be able to get around while that is shipped...

Truck is 2004 Tacoma Xtra Cab, V6, MT, 4WD.

Thanks

 

You screwed up real good there, buddy! Your ECM is definitely fried if you've got that code showing.

You basically killed the portion of the ECM that monitors and controls the throttle, and all it's sensors. When you hooked the battery up backwards, you sent a bunch of voltage the wrong way in to the ECM, and it was quick enough to get past the fuses.

I don't know how a used ECM is gonna perform. If possible, get one from a vehicle that closely resembles your truck. Get one from a 5 speed, and definitely one from an '04. I'm not sure if it's a plug and play kind of thing, though.

 

I suppose there's always the outside chance you managed to fry one or more outboard sensors instead of the ECM itself ...

... but I wouldn't bet on it.

Like kevhogaz said - if you go for a recycled ECM you need to match it as closely as possible to your original setup. It should be one for a 2003 or 2004 ('throttle-by-wire') V6 manual. I don't think an ECM from a 2001 or 2002 model will work with the throttle by wire system.

 

Thanks for the replies...

I ordered a new ECM from a salvage company in Texas yesterday, matched the OEM part number...so hopefully that will work.

Talking to the dealer they said the only thing that needs to be programmed is the VIN #...so my thought is that if I get a ECM from another vehicle it will have a VIN# already programmed...not mine, but the computer won't know that, so it should work. Ill keep my fingers crossed for now.

In the mean time I installed a battery disconnect switch under the front left wheel well... It is very effective... I shut it off when i leave the truck, turn it on when I come back and have no issues... it starts and drives just fine.

New ECM should be here Wednesday or Thursday, so more to follow then.

 

I hope the new ECM fixes your problem, I hate doling out death sentences! Good luck, and keep us posted.

 

Got the new ECM today...after it was delivered to my old apartment in the next building by mistake...

Anyway got it, part numbers matched exactly...installed it, which took all of 10 minutes since I already had the dash taken apart.

Truck started right away and no check engine light or throttle issues...

Figured I needed to drive it to be sure...but first I pulled my head unit...which was also a casualty of my idiocy. I knew that there was a fuse in the back of the head unit (a Pioneer) where the wiring harness connected plugs in...so all week Ive been crossing my fingers that thats all that was wrong...and putting off taking it out because its always a pain in the ass... Sure enough the fuse was blown, and of course it was a different kinda of fuse than toyota uses.

So I drove over to autozone to get a new fuse....no issues driving and no check engine light on the trip there or back.

So it would appear that the new ECM has solved the problem. Only thing that remains is to see if the fuse is all that was wrong with my head unit...but that will have to wait until tomorrow...its too dark to mess with that right now.

Also tomorrow I'll remove the battery disconnect switch, since its not exactly weather proof and Ive got a trip to Colorado coming up here in a couple weeks. I'll try to get some pictures before I do though incase anybody is interested.

 

Greetings ratman. Let me just say EVERYTHING you described happened to me, down to a T! Thank-you SO much for sharing this information. No doubt you've saved me a LOT of time and money! Where in Texas did you found the salvaged ECM? I'm so relieved there's a temporary fix!!

 

I used getusedparts.com to find the part. You fill out the form on their website for the part you need and they send it out to a network of used part dealers and junkyards. Whoever has the part will contact you by phone or email. I got about 5 calls and 15 emails within 24 hours of my request. The entire process made me a little nervous, but it all worked out when I got the part installed and the truck ran fine. Unfortunately I cannot remember the vendor I acutally bought the part from, I believe it was something like Smart Auto Parts. All the prices were similar, I just picked them because they called me directly and seemed to be the closest to me, although the part ended up not actually being shipped from where their office was located in Texas.

Here are some pics of the switch I installed while I waited:



Here is the switch assembly prior to install.

Heres the switch located under the wheel well.

This is looking up from the ground at the switch assembly.

This is the key to the switch

I ran the wired through this gap next to the head light.

Heres a shot of the wood spacer I made to fit the Optima in with the factory battery clamp.

 

excellent! Thank-you for the info and very good pictures of your temporary switch. Just filled-out the form on the website. Do you remember the price you paid?

 

It was about $270 with shipping.

 

well, I ordered mine for $320 and installed it today. Tried to start-up the truck, but it never turned over. It just kept cranking... Plugged the old one back in and it started-up like before. The numbers on both computers match-up, but has a different VIN programmed from the salvaged vehicle it came from.

Any ideas? Anyone?? Perhaps the damage is more extensive in my case, or I need the correct VIN programmed for this computer. But if that's the case, the truck really won't start w/out the same exact VIN? That doesn't sound right...

 

Apparently not ... 2004 ECU's had different part numbers for manual versus automatic applications.

 

The vin shouldn't matter, mine still has whatever vin it came from(not mine) and runs like a champ. I assume you had the truck running with the switch prior so all the fuses are good right? Does it look like the replacement is damaged or tampered with? Do you know what happened to the donor vehicle...ie why was it scraped? I'd say this beyond my skill level but it sounds like you may have received a bad replacement ecu...could be as simple as a software issue though...the dealer may be able to flash the replacement ecu...not sure though. Hope you can work it out. Good luck!

 

sorry guys, I tried swaping it out the night before I left for a 3-day trip to the Ozarks. Lucky to have reception at camp tonight! Thank-you for your replies. Yes, it came off a manual. All the numbers appear to match the original. Although scratched-up quite a bit, it doesn't appear to be damaged. But who knows? I guess I'm really wondering if this could mean something else can be damaged, or if this replacement is a bad unit. Based on ratman's experience, I suspect the problem is a bad replacement, but I've got to verify the problem might not be something else befire shipping it back!

 

yes, I was hoping for the same results
I started looking around online to see if a particular procedure was required to install a new ECM, but to no avail. It seems more likely the unit needs to be flashed. But can our ECM's be re-programed? I don't know...

thank-you for your assistance w/this, I just wished it wasn't going to cost at least another $100 just for the dealer to look at it!