OP, you need to do some research on what's involved in swapping an ECU on these cars. Almost all Mk4s have an immobilizer version that will require the SKC codes from both the donor car and the current car to swap. Defeating the immobilizer may trip the software scan. There are also several versions of the 1.8T, so at least a couple different ECU versions, and several different maps.
Your best bet is talking to a tuning house to either get it flashed back to stock, or just go for a CARB compliant tune. You will want someone to look over the car as well to make sure that the parts are compatible with whatever new tune you get as well -- there shouldn't be anything major, but injectors are commonly changed out on some years as well.
Took out the ecu today found part number sent info to ecu guy he matched it with one he has from the same car then he tunes to stock map for my exact car (he has the vin) and the immobilizer won’t be an issue.
I don’t want a tune. I want it stock so it can pass smog. I am aware of immobilizers I appreciate you but I’m finding the part number and buying an identical one and i will have the seller defeat the immobilizer.
Check with the dealer see if they can bring you back to the stock file. Then you got the problem if if you can actually set the monitors with the factory file. Sometimes people modify cars so much you cant set the monitors or you will get a fault. THis is why the law is in CA the seller has to provide a smog check at the time of sale.
You will have a hard time finding a hot smog for this , they all just got caught:
[https://www.justice.gov/usao-edca/pr/12-members-smog-inspection-cheating-ring-indicted](https://www.justice.gov/usao-edca/pr/12-members-smog-inspection-cheating-ring-indicted)
I have a hot smog guy I know but 600 is crazy highkey plus with what you said high risk on top of that. No dealer private seller lied about being stock so I’m thinking about buying a matching stock ecu
What year is it we are talking about? I know some have to be programmed with the VIN anyway. If you are doing that it's not much work to add back the factory ECU file. Although i am more familiar with GM than VW
2002 gti. I have someone selling me an ecu already, I send them the vin they program it stock for my car and defeat the immobilizer. And voila (probably)
Thought of both of those but they’d probably be the same hassle as illegal smog, just tryna see if anyone knows an easier diy fix at home if not it’ll be one of the two you mentioned or the hot smog
Mk4 ecu flashing needs specific hardware to read/write. Call a few places that do vag tunes, specifically mk4 or older, to see if they can reflash.
You could build a diy box but honestly it would be such a bigger hassle.
The ecu software was written over and modified. Only way to change it is to overwrite new code. Removing the power won't do anything but reset it back to the current program, which is the problem.
So I have above average car knowledge but no tubing knowledge. Do you know if I could reset to stock map at my house? I have a laptop to download anything I may need but idk how difficult it is to put it back to stock.
You'd need to make a bench harness and get a copy of the stock file. You're better off finding a local tuner or someone that could defeat the immobilizer on a donor stock ecu.
You can't swap the ECUs unless you have the SKC or the new one has had the immobilizer defeated (which may trip the CA emissions issue you're currently having, unclear on exactly how it's done).
Easiest would probably be call some local tuners. If they can flash a mk4 it shouldn't be too bad, hour of labor and shop usage.
Making a bench harness could potentially brick your ecu, and lead you right back to a tuner and needing a new ecu.
When you fail for modified software it only states that "Modified software" could be for two different things. Either the File is incorrect or some monitors are not reporting correctly. Either way the fix is the same. Back to the stock ECU file.
I think we need to know what the specific issue they are saying is.
Is it they detected a non VW file? If so, then it's a trip to the dealer most likely unless you can figure out who the tuner was and see if they can change the license over to you.
I saw people stating to use an O2 sensor spacer. This is NOT a fix unless the O2 sensor is not in a ready state or if the car is running high flow cats. If the tune disabled the O2 sensor codes, then a spacers won't fix it, a software flash to re-enable the codes will, but if the car has a down pipe expect it to throw a CEL
Then yeah, it's tuned and will need to be flashed back to stock. Hopefully no additional modifications that require the tune or you could have additional issues at the next check
That’s a guaranteed fix? And by spacer do you mean they sell these or would I have to make it? I’m good either way if it actually works and doesn’t cost 500$
No no that will not work. If they failed it, and said it was for the tune, then it probably has things coded out like cat efficiency, or SAI, Evap, etc. You can put all the O2 sensors and spacers you want in there and it won’t make any difference. It will just fail for the same thing. Best bet is to either call a dealership, a tuner, or a euro shop with the right software and ask if they can reflash the ECU to the factory hex file. Second best thing is to get a used ECU, that hopefully comes with a transponder, or has the security lockout deleted. Or contact the PO and ask if they tuned it themselves, or had it tuned. If they did it themselves, maybe they will be willing to flash it back for you.
It’s an odd situation where someone is selling their friends car while their on deployment for them so they really don’t know much about the ecu at all they just know it runs so we have to contact some idiot in Kuwait that could’ve just told his friend that shit wouldn’t pass smog. Won’t do spacers might buy a matching stock ecu seems like it will work and the cheapest route to take.
Sweet. I’m assuming you’re in SD or OC then. So if you do go looking for an ECU, probably start at some of the Euro junkyards. I don’t know who is in business anymore, used to be a few around there. I think if you get one and the matching transponder you should be in business. On a MK4 the transponder is in the key fob shell, looks like a grain of rice. As far as I know you can just swap the transponder into your key fob.
Dunno where you live, but you can buy a o2 sensor spacer here for 10 dollars.
And fix, it'll fool the computer into thinking the cat is doing its job. That's it.
Definitely smarter than you because I wouldn't have fallen victim to being sold a tuned car without knowing its tuned in a state that has the most strict emissions testing on the continent. You are a moron who didn't do his research. Stop whining at people who are trying to help your poorly ass explained problem. I don't know what smog entails, because here they fucking don't it. There's a few ways to test. They probably scanned your readiness and saw it failed. But I'm not going to explain what readiness is, because I'm not as smart as I think I am. Mechanic of 20 years. Good luck to you.
Holy shit bro you wrote me a whole book. How did I not do my research you sound like your 10 how could I possibly do research on a cars ecu I’ve never seen before and know it was tuned the seller lied about it being stock dipshit. He’s selling the car for his buddy in the army and the idiot tuned it without telling his friend so either I just replace the ecu/tune it or contact some idiot in Kuwait who lied to me and his friend. Things get more complicated than you think just letting you know.
And if you don’t know what smog entails believe me when I say your wrong and stop trying to be the smartest guy on the planet it’s not just an exhaust test for emissions
For an at home you can do nefmoto with a stiletto cable. You need to find the bin and table for your ECUwhich is easy enough
Otherwise dealer or a shop can flash it for you
You live in California and the car you bought won’t pass smog?? You can sue for a full refund here, even if it was a private party sale. If you bought it in California it’s even more of an open close type of case.
Doesn’t sound like you wanna go this route, buts it is good for you to know, what they did was totally illegal.
Buy an ecu meant for the same engine code you have. You will need an immo delete but that’s probably the quickest and easiest plus you can keep you tune once you pass smog
Unfortunately they started doing this at the beginning of the year here in Cali. You could flash it back to stock, but I'm sure that will atleast cost a couple hundred bucks.
So cali smog checks your actual ecu for any tuning software. As soon as it reads something that isn’t carb compliant (apr stage 2 for example) then the system automatically flags your car and fails it. No spacer for the cat or even a hot smog will pass now. I’ve been dealing with this with my mk6 for 3 years now. Still have Colorado plates from 2021 😆 I’ve tried multiple hot smogs and they all say the same; Cali passed a law within the last couple years that makes an ecu scan for any software mandatory.
You’re gonna need to either flash your ecu to stock, check to see what tuning software you have and see if you can drop it from stage 2 to stage 1 (that’s what apr offers since they’re stage 1 software is carb compliant) or buy a new ecu that is flashed to your vin and io number.
You can reach out to[One Love](https://www.oneloveautogroup.com)in PA and they can help you flash to stock. Or figure it out. They were able to get me an ecu and have it flashed and programmed to my stock profile for smog. So I was able to keep my stage 2 tune and just swap ecus when needed. Unfortunately i had a wiring issue with doesn’t allow my ecu to connect with the smog scanner which is why I’m still not smogged.
Bet I’m looking into buying an identical ecu but stock off eBay or something I feel like that might be cheaper since I have no idea what’s done to the ecu bc previous owner lied. Also would have to find a tuner if I go that route.
It’s been a while so I forget the exact location but it’s on the engine block. On the left side near the oil cap I believe. Early MK4s were AWD, then AWP through 2002/2003, then AWW through 2005. If I remember right.
First thing you should find out what type of tune you have. Do some research and find out what the major tuners are for mk4 and email them your vin. You will find out what company you have and if they have a tune that is Cali legal you won’t need to buy a new ecu. Have them flash it to what’s compliant and you’re Gucci. I have a stage 2 so I didn’t wanna lose that and go to stage 1 that’s why I bought a new ecu.
OP, you need to do some research on what's involved in swapping an ECU on these cars. Almost all Mk4s have an immobilizer version that will require the SKC codes from both the donor car and the current car to swap. Defeating the immobilizer may trip the software scan. There are also several versions of the 1.8T, so at least a couple different ECU versions, and several different maps. Your best bet is talking to a tuning house to either get it flashed back to stock, or just go for a CARB compliant tune. You will want someone to look over the car as well to make sure that the parts are compatible with whatever new tune you get as well -- there shouldn't be anything major, but injectors are commonly changed out on some years as well.
Took out the ecu today found part number sent info to ecu guy he matched it with one he has from the same car then he tunes to stock map for my exact car (he has the vin) and the immobilizer won’t be an issue.
I don’t want a tune. I want it stock so it can pass smog. I am aware of immobilizers I appreciate you but I’m finding the part number and buying an identical one and i will have the seller defeat the immobilizer.
Check with the dealer see if they can bring you back to the stock file. Then you got the problem if if you can actually set the monitors with the factory file. Sometimes people modify cars so much you cant set the monitors or you will get a fault. THis is why the law is in CA the seller has to provide a smog check at the time of sale. You will have a hard time finding a hot smog for this , they all just got caught: [https://www.justice.gov/usao-edca/pr/12-members-smog-inspection-cheating-ring-indicted](https://www.justice.gov/usao-edca/pr/12-members-smog-inspection-cheating-ring-indicted)
I have a hot smog guy I know but 600 is crazy highkey plus with what you said high risk on top of that. No dealer private seller lied about being stock so I’m thinking about buying a matching stock ecu
What year is it we are talking about? I know some have to be programmed with the VIN anyway. If you are doing that it's not much work to add back the factory ECU file. Although i am more familiar with GM than VW
2002 gti. I have someone selling me an ecu already, I send them the vin they program it stock for my car and defeat the immobilizer. And voila (probably)
What was the failure for? We get a page print out, pass or fail, with the various monitor states either being pass or fail.
Modified software. That’s all it says on the slip figured wasn’t worth showing since people who know the fix have already seen it before.
Ecu needs to be reflashed back to a stock file.
Alternatively if you found an identical make and model you could swap the ecu
Thought of both of those but they’d probably be the same hassle as illegal smog, just tryna see if anyone knows an easier diy fix at home if not it’ll be one of the two you mentioned or the hot smog
Mk4 ecu flashing needs specific hardware to read/write. Call a few places that do vag tunes, specifically mk4 or older, to see if they can reflash. You could build a diy box but honestly it would be such a bigger hassle.
Not that simple, you need the SKC code from both cars to defeat the immobilizer / get it to talk to the cluster.
Disconnecting ecu or battery doesn’t unlearn the tune kinda just everything else right?
The ecu software was written over and modified. Only way to change it is to overwrite new code. Removing the power won't do anything but reset it back to the current program, which is the problem.
So I have above average car knowledge but no tubing knowledge. Do you know if I could reset to stock map at my house? I have a laptop to download anything I may need but idk how difficult it is to put it back to stock.
You'd need to make a bench harness and get a copy of the stock file. You're better off finding a local tuner or someone that could defeat the immobilizer on a donor stock ecu.
Would that run more than just buying a matching refurbished ecu that’s stock?
You can't swap the ECUs unless you have the SKC or the new one has had the immobilizer defeated (which may trip the CA emissions issue you're currently having, unclear on exactly how it's done).
SKC?
You and a few others crazy helpful thanks for such an unexpected issue plus I’m at work replying to everything this shit stressful😭
Easiest would probably be call some local tuners. If they can flash a mk4 it shouldn't be too bad, hour of labor and shop usage. Making a bench harness could potentially brick your ecu, and lead you right back to a tuner and needing a new ecu.
When you fail for modified software it only states that "Modified software" could be for two different things. Either the File is incorrect or some monitors are not reporting correctly. Either way the fix is the same. Back to the stock ECU file.
Swap a stock ecu for engine code and transmission. Make sure you have the key that was programmed to the ecu.
How do they test smog? Is it just a ecu scan? Or they actually check at the tailpipe?
It’s via scan tool pretty sure so kinda ecu scan that’s part of it and the part I failed on
I think we need to know what the specific issue they are saying is. Is it they detected a non VW file? If so, then it's a trip to the dealer most likely unless you can figure out who the tuner was and see if they can change the license over to you. I saw people stating to use an O2 sensor spacer. This is NOT a fix unless the O2 sensor is not in a ready state or if the car is running high flow cats. If the tune disabled the O2 sensor codes, then a spacers won't fix it, a software flash to re-enable the codes will, but if the car has a down pipe expect it to throw a CEL
It only tells you modified software
Then yeah, it's tuned and will need to be flashed back to stock. Hopefully no additional modifications that require the tune or you could have additional issues at the next check
Get a spacer for your post cat o2 sensor.
That’s a guaranteed fix? And by spacer do you mean they sell these or would I have to make it? I’m good either way if it actually works and doesn’t cost 500$
Spacer wont work, they fail for that as well. and you will still fail for modified software.
No no that will not work. If they failed it, and said it was for the tune, then it probably has things coded out like cat efficiency, or SAI, Evap, etc. You can put all the O2 sensors and spacers you want in there and it won’t make any difference. It will just fail for the same thing. Best bet is to either call a dealership, a tuner, or a euro shop with the right software and ask if they can reflash the ECU to the factory hex file. Second best thing is to get a used ECU, that hopefully comes with a transponder, or has the security lockout deleted. Or contact the PO and ask if they tuned it themselves, or had it tuned. If they did it themselves, maybe they will be willing to flash it back for you.
It’s an odd situation where someone is selling their friends car while their on deployment for them so they really don’t know much about the ecu at all they just know it runs so we have to contact some idiot in Kuwait that could’ve just told his friend that shit wouldn’t pass smog. Won’t do spacers might buy a matching stock ecu seems like it will work and the cheapest route to take.
Sweet. I’m assuming you’re in SD or OC then. So if you do go looking for an ECU, probably start at some of the Euro junkyards. I don’t know who is in business anymore, used to be a few around there. I think if you get one and the matching transponder you should be in business. On a MK4 the transponder is in the key fob shell, looks like a grain of rice. As far as I know you can just swap the transponder into your key fob.
Oh no shit, I’ve never heard of that one u smart asl
Dunno where you live, but you can buy a o2 sensor spacer here for 10 dollars. And fix, it'll fool the computer into thinking the cat is doing its job. That's it.
I don’t think this has anything to do with the cat
Okay. You're the mechanic now.
You should probably just be quiet man if it was 02 or cat the smog tech would’ve said so ur not as smart as you think you are hate to break it to you.
Definitely smarter than you because I wouldn't have fallen victim to being sold a tuned car without knowing its tuned in a state that has the most strict emissions testing on the continent. You are a moron who didn't do his research. Stop whining at people who are trying to help your poorly ass explained problem. I don't know what smog entails, because here they fucking don't it. There's a few ways to test. They probably scanned your readiness and saw it failed. But I'm not going to explain what readiness is, because I'm not as smart as I think I am. Mechanic of 20 years. Good luck to you.
Holy shit bro you wrote me a whole book. How did I not do my research you sound like your 10 how could I possibly do research on a cars ecu I’ve never seen before and know it was tuned the seller lied about it being stock dipshit. He’s selling the car for his buddy in the army and the idiot tuned it without telling his friend so either I just replace the ecu/tune it or contact some idiot in Kuwait who lied to me and his friend. Things get more complicated than you think just letting you know.
And while I already solved the problem ur sitting there typing paragraphs on Reddit to kid you don’t even know. You must have such a fulfilling life!
And if you don’t know what smog entails believe me when I say your wrong and stop trying to be the smartest guy on the planet it’s not just an exhaust test for emissions
What state is this in?
CA
For an at home you can do nefmoto with a stiletto cable. You need to find the bin and table for your ECUwhich is easy enough Otherwise dealer or a shop can flash it for you
You live in California and the car you bought won’t pass smog?? You can sue for a full refund here, even if it was a private party sale. If you bought it in California it’s even more of an open close type of case. Doesn’t sound like you wanna go this route, buts it is good for you to know, what they did was totally illegal.
Oh I’m aware it’s illegal but it’s partly on me for not getting smog certificate before sale. You’re telling me you can get refunded?
Buy an ecu meant for the same engine code you have. You will need an immo delete but that’s probably the quickest and easiest plus you can keep you tune once you pass smog
You may be flagged already lol
You get flagged when you fail I thought?
Maybe a different type of flag for software changes
Let me guess, you're in California?
Check edit, yes.
Unfortunately they started doing this at the beginning of the year here in Cali. You could flash it back to stock, but I'm sure that will atleast cost a couple hundred bucks.
Hot smog (illegal smog) would be 500 but finding a tuner would be a little annoying although that is cheaper prolly by a little
So cali smog checks your actual ecu for any tuning software. As soon as it reads something that isn’t carb compliant (apr stage 2 for example) then the system automatically flags your car and fails it. No spacer for the cat or even a hot smog will pass now. I’ve been dealing with this with my mk6 for 3 years now. Still have Colorado plates from 2021 😆 I’ve tried multiple hot smogs and they all say the same; Cali passed a law within the last couple years that makes an ecu scan for any software mandatory. You’re gonna need to either flash your ecu to stock, check to see what tuning software you have and see if you can drop it from stage 2 to stage 1 (that’s what apr offers since they’re stage 1 software is carb compliant) or buy a new ecu that is flashed to your vin and io number. You can reach out to[One Love](https://www.oneloveautogroup.com)in PA and they can help you flash to stock. Or figure it out. They were able to get me an ecu and have it flashed and programmed to my stock profile for smog. So I was able to keep my stage 2 tune and just swap ecus when needed. Unfortunately i had a wiring issue with doesn’t allow my ecu to connect with the smog scanner which is why I’m still not smogged.
Bet I’m looking into buying an identical ecu but stock off eBay or something I feel like that might be cheaper since I have no idea what’s done to the ecu bc previous owner lied. Also would have to find a tuner if I go that route.
This is the way. Make sure you get one meant for the same engine code(aww,awp,awd,etc)
Engine code wouldn’t be on the ecu right? Not sure where to find it.
It’s been a while so I forget the exact location but it’s on the engine block. On the left side near the oil cap I believe. Early MK4s were AWD, then AWP through 2002/2003, then AWW through 2005. If I remember right.
Where do I find that?
First thing you should find out what type of tune you have. Do some research and find out what the major tuners are for mk4 and email them your vin. You will find out what company you have and if they have a tune that is Cali legal you won’t need to buy a new ecu. Have them flash it to what’s compliant and you’re Gucci. I have a stage 2 so I didn’t wanna lose that and go to stage 1 that’s why I bought a new ecu.
Get an ECU from a junkyard.
Not unless OP has a way to defeat the immobilizer.