CEL on, code P0604 "Control Module Random Access Memory error"

[dyvyd]

Hi Folks,

i've searched the forums several ways for hours to try to find something on this but no luck, so please forgive me if there is a thread i've somehow missed or not searched quite right.

i've got a '98 Jetta TDI 5-speed and have had persistent problems with the Check Engine light coming on. Generally comes on about 30 seconds after starting & stays on. For a while i had problems with intermittent power loss, first accelerating to pass at highway speeds (75-80 MPH) then later only when shifting up through the gears, usually while accelerating to shift from second to third & third to fourth gear. My mechanic cleaned the intake manifold and adjusted the timing and it seemed fine for quite a while. i haven't had the power loss symptoms of late but the CEL is coming on again.

My mechanic got the P0605 code & took the ECU out & cleaned out the line from inside it and that seemed to clear it but only briefly. About 150 miles after that the CEL came on again as before. Now gets code P0604--Control Module Random Access Memory error. My mechanic thinks he should just replace the control module--does that sound right? i've talked to other folks who say it's actually very rare that the module has to be replaced and it's usually a vacuum line problem or possibly MAP problem. Any advice? i would hate to replace the control module and still have the CEL problem (i'm overdue for MA state inspection already with the back-and-forth on how to fix this).

Also, any recommendations on after-market control modules or is it a bad idea to use an after-market replacement module? i searched a little and found OEM modules for $771 (best price i found with a list over $900!!) and after-market units for $231 to $238. If i have to buy the module, any recommendations on where to order/buy (US)?

My apologies for the long post and my thanks in advance for any help and advice anyone can provide.

 

[Nutsnbolts]

It is indeed very unusual to have an ECM go bad these days. But, the P code is indicating that something in the ECM is indeed faulty. I would scan it with VagCom first, just to make sure, then contact a salvage yard to source one. It will be tough to find, but they are out there.

-Rich

 

[jcrews]

Was the internal pressure pipe just cleaned or replaced? That old piece isn't worth putting back in, and it may have split after being handled.

I don't know why, but these units do throw a 65535/P0604 checksum error when the pressure sensing lines leak. It's worth a second look before throwing a new ECM at it.

 

[dyvyd]

Thanks to Nutsnbolts . . . may try to locate one from a salvage yard. The only codes we've gotten have been the P0605 before he blew out the ECM internal vacuum line and then subsequently after the CEL came back on got P0604, the control unit memory error.

jcrews--internal line in the ECM was just clean & NOT replaced--my mechanic insisted it wasn't leaking but only appeared to have some blockage & he cleared it by blowing it out with an air gun in opposite direction to vacuum flow & that it cleared. He is convinced that the ECM needs to be replaced. i thought about going to someone else but the guy i was going to see from the trusted mechanics list ended up in the hospital the day i was going to bring the car to him. i guess i'll just try to press my guy to try replacing the line--and maybe have him do all the vacuum lines as i've heard it's good to replace the cloth-covered lines with silicone based lines of the same size.

Thanks again.

david

 

[Vince Waldon]

Look for a break in the hose.. all the way *inside* the ECU... and dollars to donuts you're gold:

There are a million perfectly good pre-1995.5 ECUs out there sitting in various garbage piles... all due to a little tiny crack in the hose.

Having said that... the 100+ psi air from the mechanic's air hose may have ruptured the pressure transducer on yours... but it's worth another peek?

 

[Nutsnbolts]

Based on the above posts, I certainly learned something here. I would have expected a completely different code for the ruptured hose, but perhaps it interprets an implausible boost signal as a module error!

I would back up Vince's and Jcrews advice, since they have seen this very failure.

Remember, as I have said before, the ECMs RARELY go bad.

Check that hose!

-Rich

 

[dyvyd]

Thanks . . . question--"pressure transducer"

Vince (and everyone),

Thanks for all the helpful info . . . .

Having said that... the 100+ psi air from the mechanic's air hose may have ruptured the pressure transducer on yours... but it's worth another peek?[/QUOTE]

If my mechanic's using the air hose to clear the ECM vacuum line ruptured the pressure transducer, would the car still run Ok? It seems to be running fine, fuel mileage is pretty good and no driving problems.

Apart from that, now just need to convince my mechanic to try the fix & replace the line inside the ECM. i decided based on various posts to go ahead & replace ALL vacuum lines. Bught silicone rubber line as recommended by Paramedick in a thread on vacuum lines, but haven't found the 4mm stuff yet, will have to order on line. i know someone posted a source at a good price ($.72/ft less than i paid at a local parts shop) but i have to search & find it.

i'll let you all know what gives when the problem is fixed & i've got a sticker (MA inspection, overdue since 31st March).

FYI, i googled '98 Jetta TDI engine control module & got loads of good stuff including several links to threads here on TDIClub. i found multiple possible sources for replacement or re-manufactured or used ECMs. When i figure out where to post it, i'll put together a list & what info i have. There were a few for searching salvage yard inventories for the part. i found one in Alabama for $320 including shipping. i'm not going to buy the part though unless i have no choice. i found site that offers the ECM (new, VW replacement part) for $771 & shows a list of $975 or so.

Thanks again to all.

david

 

[dyvyd]

Vacuum lines done, still have error

Hi All,
Thanks again for the info. My mechanic replaced all the vacuum lines including the one inside the module & Check engine light still comes on about 30 seconds after starting, still getting the control module error so we're going to replace it. i added a post in the classifieds section to look for it & submitted queries to a few places after searching on the web. AutoComputerSyseters.com has OEM part for $599.95 plus S&H. Think i'll hold out for a used one. Anyway, just wanted to say thanks to you.
david

 

[jcrews]

Assuming the code was actually erased first [], do you see atmospheric pressure on the MAP output display in VCDS?

 

[dyvyd]

Good question . . . . i wasn't actually there when the scan was done and i don't know if he erased the code first. i will ask, though. Got to talk to the mechanic tomorrow about possibilities for buying the control module anyway. i'm reallyll not savvy on this stuff myself. i assume it should show atmospheric pressure on the MAP output based on conditions at the time? Or am i out to lunch here?
Thanks again. david

 

[jcrews]

The MAP should read about 100kPa (1000mbar) with the engine off. I'd recommend a full during-performance scan (3rd gear 1800->3500 RPM @ 100% throttle).

In the case that there really is a ROM checksum error, removing and reinstalling the memory chips (they are PLCCs) may be enough to correct the problem. Otherwise, any competent chip tuning outfit should be able to read the existing program ROM, validate it against a known good sample, and load new chips with good images if required. You can get an upgrade remap in the process, too, if desired.

Replacing the entire controller should be considered a last resort (physically destroyed hardware).

 

[dyvyd]

Ok--i can ask my mechanic to run that test. i understand what you're saying about the memory chips, i've messed with memory modules for computers @ work & home but i'm leery of messing with the module myself, not sure if my mechanic would either.

The other problem is i can't handle too much time without the car so i'm tempted just to go ahead & replace the module since i've gotten a couple offers for used ones pretty reasonable ($200). One is from a VW/Audi tech & if i interpreted his message correctly, it's been factory serviced. Sending the module to be serviced means time without the car but i dont' have back-up trans & can't afford to rent a car for a few days. i'm guessing i would wind up spending about the same money for the module service although clearly i'd have more certainty about the module when it goes back in the car.

IF i were to have a tuning outfit service the module, who do you recommend? What's typical turn-around time for that if you know?

Sorry for the long post & thanks again for your thoughtful help & patience.

best,

david

 

[dyvyd]

The last few months have been crazy for a lot of reasons so i haven't had much time to log in but i wanted to send a very belated THANK YOU to all of you--Nutsnbolts, JCrews & Vince Waldon--for the info & insights you provided. After having all the vacuum lines replaced, including the one inside the original ECM, with silicone rubber tubing & clearing the system & re-scanning, still had the same error code & check engine light on. So i got a used ECm from another member ($100 incl. priority mail shipping), had my mechanic replace the vacuum line inside the 'new' ECM & voila, clearing the system & re-scanning did the trick. Car runs better & no error codes. i kept the old ECM & would like to get it bench-tested somewhere but i'm not in a hurry to do that. If it's actually viable or reparable for a reasonable price (i never tried pulling the chips in it & reinstalling them) i might think about getting it chipped & putting it back in. Anyway, thanks again.

regards,

david