PCM (ECU) is officially dead - options for replacement?

Hello All,

After finally getting my daughter's P5 running well (see thread here), after about 100 miles, it started back with a high idle (only 1500 RPM this time) and a new twist - an RPM fluctuation on deceleration. This thing is driving me crazy!

So, double checked for vacuum leaks and proper operation of the sensors, including watching live data on my borrowed scan tool... nothing seemed amiss except for the high idle (which now came complete with a 0507 DTC code) and the RPM fluctuation on deceleration. Finally threw up my hands and took it to the local import mechanic, who pulled up a TSB (#01-028/03) describing this very problem - caused by "improper idle speed control logic". And the solution was to reflash the Power Control Module (PCM). Great - now I have to go to the dealer.

Today, the dealer connected to the PCM, started the reflash procedure, things were going swimmingly and ... nothing. The PCM died on the table. All gone; no life left. They tried numerous revival procedures - nothing. Now the car won't run at all.

So, now I have to find another PCM. A new one is $1200 and is on back-order from Japan; probably weeks away. The P5 is a 2003 with an Automatic tranny w/speed shifter. (The PCM part number is FSBB 18-881C). I can find a used PCM on eBay and the dealer will install and flash for me, but not sure if this will work properly. Does anyone know if swapping in a junkyard PCM will work, and if so, is it just a drop-in, or if not, what steps are necessary to get it to run properly and pass smog, etc?

Thanks,

Melsman

Should be a drop in replacement, at least on the manuals it is

Progress so far....

The PCM contains the VIN and current mileage of the vehicle, plus other pertinent hard-written data, so just dropping in an ECU (PCM) from another vehicle may allow it to run, but when scanned for smog and other issues, the VINs won't match, causing other issues. Anyway, I have found that a company called GoECM.com rebuilds ECM's and returns them to a blank state, and then resales them. As luck would have it, they just sold the last FSBB 18-881C in stock. However, they offer a "rebuild" service so that the dealer (who will have to reprogram the PCM) can reenter the VIN, etc., and then re-flash the computer. So here are my options so far:

1. Have the dealer (who's housing the P5 right now) send the bricked PCM to the GoECM guys to bring back to life and send back to the dealer - for $295: Moderate risk factor; low $ figure; or
2. Buy another salvage PCM for around $120, send it to GoECM for a rebuild, and they send it to my dealer for flash and installation: Lower risk factor; moderate $ figure; or
3. Wait for two months for a back-ordered new part from Japan at $1200: No risk factor; BIG $ and PITA factor; or
4. Push this thing off of a cliff. Huge SATISFACTION factor...

More and more, I'm leaning towards #4...

Melsman

I've got $200 before you push it off a cliff

But seriously $1200 is bs. Ecu is an ecu, never heard of them storing vin and milage as people have ran the MP3 ecu in California without issue

If the dealer can re-enter the VIN and other info then why would rebuild even be necessary? Get one from junkyard and have dealer reflash it. Why would ecu need to keep mileage data? That has nothing to do with keeping the motor running. Isn't that just in the gauge cluster? Because if you change out cluster it won't magically pick up mileage from the ecu and change what you see, it just keeps going from where it left off from previous vehicle. I'd also say, the ecu was working (maybe not as good as it could but still working) before the dealer tried reflash, maybe they did something wrong to kill it and should be replacing it at their cost.



Also, let me check to see which extra one I have. I do have sportronic but the spare ecu I have may be just from the regular automatic. I can check it out after work to see if it is the 881C. I had gotten one for another project and didn't use it.

i12drivemyMP5 said:

If the dealer can re-enter the VIN and other info then why would rebuild even be necessary? Get one from junkyard and have dealer reflash it. Why would ecu need to keep mileage data? That has nothing to do with keeping the motor running. Isn't that just in the gauge cluster? Because if you change out cluster it won't magically pick up mileage from the ecu and change what you see, it just keeps going from where it left off from previous vehicle. I'd also say, the ecu was working (maybe not as good as it could but still working) before the dealer tried reflash, maybe they did something wrong to kill it and should be replacing it at their cost.



Also, let me check to see which extra one I have. I do have sportronic but the spare ecu I have may be just from the regular automatic. I can check it out after work to see if it is the 881C. I had gotten one for another project and didn't use it.

Click to expand...

Older cars have mileage tracked in the cluster, as i12drivemymp5 mentioned. You should be able to drop in another ECU, connect it and go without having the dealer do anything.

+1 If I remember correctly our ecu doesn't have that info stored in it.
I passed smog here in VA with a mazdaspeed ecu(turbo) on my p5 with out any issue. Just plugged it in no changes or flashes, many people have done this with out any issue

Howdy All,

First -thank you for the responses. I ended up buying a "rebuilt" PCM from GoECM.com (nice folks) and the dealer was able to reprogram/update this one. But when the car started... the high idle and fluctuating deceleration was back just like before! So, I had them run additional diagnostics. It continues to act like there's a vacuum leak; screwing in the AAS has no effect on the high idle. Searches for vacuum leaks provide no results. So, the theory at this point is a bad throttle body. Happened to find a salvage yard close by with a 2003 P5 and bought the TB. Cleaned it up, checked the throttle position sensor (TPS) - 4.6 kOhms total and smooth resistance throughout travel. The IAC is 8.5 ohms and operates freely. So both are within spec. I'm installing it a couple of days from now. I'll let you know what happens.

I think you need a new mechanic...

Tgrottle body doesn't go bad btw.

Did they ever check the intake tube for cracks?

New mechanic, I agree. The PCM was never bad. Those things get blamed too often. Just because the mechanic doesn't understand the issue doesn't mean it's some computer voodoo.

Whenever anyone complains of idle issues - high, low, inconsistent - I just think "Yeah, sounds about right for this engine". I've been driving this car for 100,000 miles, the only thing consistent about this engine is that it's consistently inconsistent.

Did you check your current IAC and TPS?

I would check for vacuum leaks around the intake with a can of starting fluid.

Do you have any exhaust leaks before the 2nd O2 sensor. Everytime that I've had an exhaust leak in this area, it has affected my idle.

Sorry, didn't get back quick but woulda been no help. The extra I have is wrong one, it is FSAR 18-881.

Thanks for the replies, guys. I appreciate it. The good news is, I solved the problem!

I stumbled across some threads that mentioned the high idle and pulsing RPMs on deceleration, and connected this behavior with adjustment of the Throttle Position Screw (TPS), which I had "adjusted" early on in an effort to resolve a low idle issue. However, as I read through the Mazda bulletin that covers a technique for resetting the TPS, I noticed a reference to not damaging the "gray sealing compound" in the TB throat - the very stuff that I had scraped out in the belief that it was carbon build-up! So, to make a long story short (Here's a link to the long story...), after resetting the TPS and replacing the sealant, the car runs beautifully - actually runs better than it did before.

Now my hair can start growing back in.

Melsman