what would happen if you installed a 5spd ecu in auto car with no recode?

So I'm wondering what would happen if you installed an ECU from a 5spd car in an automatic car but failed to recode the ECU in VCDS?

Car is a 2001 ALH Jetta.

The immobilizer would keep you from doing much of anything except sitting there cussing.

Prairieview said:

The immobilizer would keep you from doing much of anything except sitting there cussing.

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assuming the immobilizer has been dealt with.

Maybe not run as well? Different injectors and bigger pump, not really sure. All I know is they have a different soft coding lol

Only thing I can think of is the manual has a 120amp alt. to run the coolant
glowplugs,which probably would change nothing.

My Beetle still has the original ECU - recoded from 4 speed automatic to 5 speed manual when that conversion was done. As far as the engine working - no issues ( and now I have an RC stage 2).

You could sit and listen to the radio, scratch your nose, ruin your wifes day, find Jesus etc. If you recoded for the immobilizer, the engine would run, however you tranny would probably not shift correctly. These cars run on software and it is mandatory the software coding is correct to have the car function correctly.

scooperhsd said:

My Beetle still has the original ECU - recoded from 4 speed automatic to 5 speed manual when that conversion was done. As far as the engine working - no issues ( and now I have an RC stage 2).

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Not even close to what the OP is trying to do.

So the TCM doesn't function on it's own?

Ol'Rattler said:

Not even close to what the OP is trying to do.

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Not trying to do.

Here's the story guys.

Bought an 01 automatic ALH owner said auto tranny was shot, forward gears didn't work, reverse worked. A while ago he had immobilizer issues and a local shop replaced the ecu/key etc.

I pop in a 5spd and go to recode the ECU in VCDS and the thing is already set to manual (00002). Take it for a test drive no fault codes, etc. Although I don't think cruise is working but that might be something else.

Now I'm thinking that the auto tranny wasn't really bad to begin with but was running in some sort of "open loop" mode and over time either that destroyed his tranny or it just didn't work correctly right from the get go and got worse. Within a short period of time after the immobilizer service record I also have one for a rebuilt turbocharger, so perhaps there was a misdiagnosis... who knows. Just more for my knowledge bank than anything else I guess.

Sounds like whoever did the work didn’t know what they were doing. Yeah I can’t see the transmission working well, if at all.

You may very well have a working transmission. Though I think I would quiz the former owner before I used or sold it.

Look up CoolAirvw and ask him

leafs said:

Although I don't think cruise is working but that might be something else

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If they didn’t recode the transmission, what makes you think they turned on the cruise control. Open the engine>login screen in vcds and it should tell you the code to turn it on.

KyleMillione said:

If they didn’t recode the transmission, what makes you think they turned on the cruise control. Open the engine>login screen in vcds and it should tell you the code to turn it on.

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Not sure if this is the cause (haven't had a chance to take it around the block again yet, it's unregistered and uninsured right now heh... can't get caught slippin by the popo so I'll wait until after dark) but the clutch cruise switch wasn't being closed by the clutch pedal. I pulled out the little rod on the switch a bit (it has this ratchet mechanism) and now it closes when the clutch pedal is depressed. So I will see if that fixed the cruise problem if not then to VCDS it is.

Judging by this shops facebook page they specialize in these cars and there's pics of them doing elaborate swaps, etc... so I really hope they didn't slip up like this... I mean maybe. I'm going to give them a call just to feel em out a bit to see what they did. They probably don't remember but it's pretty easy to get a general sense if it sounds like they know what they're doing. Feel bad for the older dude who sold it to me for cheap.

I had the same problem on my 5 speed conversion where I recoded for a manual transmission in VCDS and it seemed like it did not change how the car behaved. I took the car out for a test drive and had multiple ECU fault codes for various systems other than the engine. Redoing the manual coding '02' and setting the injection pump IQ solved the fault codes and the drivabilty problems. I have found the hard way that recoding and seeing the recode value in the adaption screen does not mean the ECU has actually accepted the value. Such ghosting can be a problem with the MK IV ECUs.

Did you use a VCDS to confirm the manual setting in the ECU?

good news: cruise works (don't know if adjusting the switch fixed it or activating in VCDS caused it to work)

bad news: no cruise control light on dash.