# 1.8t mk4 crank no start and not talking to ecm



## Vinnie Vegas (Jan 5, 2014)

I recently bought an 01 jetta1.8t from a friend. Running. It has a misfire. I fixed that with a coil. Test drove and found small vacuum leaks. Fixed that. Moved car two more cars and now it doesn't start. Randomly I go out and try starting. Some times it works most of the time doesn't. When it doesn't run. I can't check for codes. When it does run. It has 4 codes. O2 sensor and secondary intake. Which was removed and blocked off. I can't find anything wrong. Ok where to look. And ideas or help??


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## 97jett (Sep 10, 2008)

this just happened to my car and came out to be the fuel pump, so thats a possiblitly


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## DMVDUB (Jan 11, 2010)

Fuel Pump Relay

Fuse

Crank Position Sensor

it's one of those :wave:


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## Vinnie Vegas (Jan 5, 2014)

Already swapped fuel pump relay. And replaced fuel pump. Also checked all fuses. The crank sensor could cause the car to not let me check for codes?


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## DMVDUB (Jan 11, 2010)

Vinnie Vegas said:


> Already swapped fuel pump relay. And replaced fuel pump. Also checked all fuses. The crank sensor could cause the car to not let me check for codes?


no.


Sounds like you have a loose connex


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## Vinnie Vegas (Jan 5, 2014)

Removed battery and cleaned all grounds I could find in the engine bay. Several under battery tray and a few under windshield. Still no luck. Tried swapping 100 relay with another. No change. Also inspected the o2 sensors as best as I could but the car is so low and hard to lift with floor jacks. I heard those have been know to be a problem with no start. Idk if that's true. How do I check if my ECM is even powering up? I'm pretty sure I heard my fuel pimp prime when key turned over. Despite of being able to check for codes. Cuz when the car runs. It shows me the codes.


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## DMVDUB (Jan 11, 2010)

the codes you see when it's running are probably unrelated. I don't remember, you need to find the pinout map for the obd2. There should be a power and a ground in there and you put a multimeter to it. There's a description somewhere on google how to do it. I'm way too lazy to find it for you.


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## rstolz (Jun 16, 2009)

did you check the battery charge? should be 12.34V, 12V is too low. The system is that sensitive.


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## Vinnie Vegas (Jan 5, 2014)

Well I just tried charging the battery and had my booster pack on it. With volt meter I only showed 11.4tops same with lights on.


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## Vinnie Vegas (Jan 5, 2014)

12.5 dropped to 11.4 while cranking


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## Dave926 (Mar 30, 2005)

Battery is fine.

Tach will usually jump assuming the G28 crank pos sensor is in good condition.

Never tried this, but with VAGCOM try watching block 1 while cranking. Should see rpm

If you want to test the Crank sensor with a DVM, I believe the spec is 700-900 ohms on a good sensor


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## zaskar (Jan 17, 2000)

the fact that you can't scan it when it doesn't start let me think the ecm relay does not click, next time it doesnt start, remove the 428 relay in the engine bay close to the brake booster and jump the two large pin with a wire, try to connect with your scanner and start. if it does, then either the relay itself or a wiring problem. at least you'll be closer to finding the problem.


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## AmIdYfReAk (Nov 8, 2006)

No one asked if it has a aftermarket radio installed yet? =]


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## Vinnie Vegas (Jan 5, 2014)

Stock radio. Removed 428 fuse installed wire for two big post. Tried to start and nothing. Still can't read codes.


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## BMXican37 (Jan 24, 2007)

Well does it have spark? Fuel pressure? Compression? Before you start throwing expensive sensors at it why not start with seeing if it has the 3 main sources of combustion instead of guessing


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## rstolz (Jun 16, 2009)

expensive sensors? a crank sensor is $20, and takes all of 5-15 minutes to replace depending on how much cladding you have to remove.

however, a bad crank sensor would not interfere with being able to read the ECU

If you can't even scan the thing and the battery's fine, then you have a power supply issue to the ECM. Don't bother with fuel, compression or spark until you've chased down the electrical gremlin interfering iwth ECM communication. 

could be a bad ground, faulty relay or short caused by split wires. 

Because you said you get an 02 code when it does fire, I'd check those wires first (both 02 sensors), it's very possible they ended up burning thru the casing and are shorting intermittently.


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## BMXican37 (Jan 24, 2007)

I didn't say a crank sensor is expensive I'm saying if you keep guessing and throwing parts and sensors at a car that you have no clue on what the problem is first then yes it gets expensive that being said ....why would you tell the kid not to look for spark fuel and compression before looking at an electrical issue which is the most annoying and hardest thing to find.. Working backwards is time consuming instead of looking for an electrical issue witch could be 5000 possibilities .wouldn't you want to see if you have 3 main keys of combustion???...you could tell if the ecu has power if the fuel pump is turning on while cranking by checkin fuel psi (fuel) you could tell if you have ecu power and crank sensor signal if you have spark and injector noid (fuel, spark) by seeing if you do or do not have spark and fuel you can determine what direction to go so ya checking those things first is a good idea.. I'm not saying it's not an electrical issue it very well might be and it sound like it does but don't go and search for a problem that might not be there first always go with the easiest things to check first ..and just because your ecu isn't communicating with your scanner doesn't always mean bad ecu or a short


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## DMVDUB (Jan 11, 2010)

rstolz said:


> expensive sensors? a crank sensor is $20, and takes all of 5-15 minutes to replace depending on how much cladding you have to remove.
> 
> however, a bad crank sensor would not interfere with being able to read the ECU
> 
> ...


 Could've sworn I said this earlier... nooooo don't listen to me, a multimeter and google are too hard to use. :banghead:


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## rstolz (Jun 16, 2009)

BMX... 
the car starts and runs intermittently, which means spark and fuel intermittently... Battery tests fine... no signal to ECU from jumping the power supply relay...

learn to read the symptoms. not every symptom should follow the same procedure for diagnostics...

DMVDUB, 
related, but not quite the same. You give one specific test, i stated to generally start chasing the electrical issue, it was more agreement that restatement. Though honestly that's probably not where I would start, but it's really a matter of preference at that point.

I'd start with a voltage check of the power supply relay pins (basically done), then check the ignition switch 12V lines, then back to the "micro-centric" relay panel under the dash and the fuse panel, then the fuse panel at the battery. Find out where the voltage stops and you've found your issue.

A bit tedious maybe, but not terribly difficult if you know the wires to test.


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## BMXican37 (Jan 24, 2007)

Look We can go back and forth all day saying what it could be.. I'm trying to help with a place to start, not start a battle of wits and I didn't read anywhere where he said bypassed the ecu power relay and read on a multimeter that there isn't power?? he said he bypassed a fuse which really doesn't do anything? Unless the fuse is blown..the only symptom of no power to ecu is no communication with the scanner and if I'm correct he said he heard fuel pump prime ... like I said before you can tell if there's power to the ecu simply by popping a coil off and checking for spark or by checking for fuel psi or injector noid not a very hard thing to check ..I'm saying it gives you a direction if you have neither it's most likely a ecu com problem if you have one or the other than look for a problem in that specific system


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## gtiguy12 (May 22, 2006)

With the key on and the engine off, when the vehicle will not start or communicate, does the check engine light illuminate on the instrument cluster?


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## Vinnie Vegas (Jan 5, 2014)

No I don't see a check engine light on when key is turned to on. Tried also when cranking and nothing. Gonna check those 02sensors.


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## Vinnie Vegas (Jan 5, 2014)

And o2 sensors look fine. Someone tell me which wires to check at the ECM or fuse box. I'm not good at electrical. But I'll try or where to find the diagrams.


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## Vinnie Vegas (Jan 5, 2014)

Is the radio supposed to blink when no key in the ignition? Goes away when turned to on


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## Yareka (Mar 5, 2002)

It was mentioned above but you need to be able to communicate with the ecu and see the CEL in the cluster before you start doing anything.
Unplug the ecu and check for power and ground, that will rule out the ecu or tell you whether you need to look further back in the wiring.


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## BBSRGRs (Apr 30, 2013)

anyone find a solution to this? having same problem however it's not intermittent, it just wont start but cranks strong, cant communicate with ECU, no check engine or EPC light when key turn to "on" position, how can i check the ECU is getting proper power? i cznt seem to find much on any of this


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## robin_bga (Jun 23, 2011)

Hi Vinnie, also on yo list check for fuses 12 for the diagnostic port.
29, 32 $ 34.
If all those are good then u should have to replace the CPS sensor, and just so you know, an o2 sensor can not refuse a car to start maybe light up the check engine light but nit refuse to start.
If u want to manually check the ECU voltage, there many ways;
Check the fuses I told to above $ also check their voltages.
Check for spark
Remove the ecu relay 428 in the engine bay $ check for voltage one one of the big terminals n the ground. etc
N guys lets we are here to help, it doesn't matter how u bring the solution provided it helps the victim its up to the victim to choose on how to approach it.
We should be good.
Cheers bros....


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## jalisco (Sep 1, 2010)

Have you fixed this yet? I have the same problem and I tried different ECUs and Nothing 😔


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## jeffpepin (Apr 12, 2015)

exactly the same problem on mk4 jetta 2.0l AEG 
motronic M5.9.2 , 
hardwired +12VDC (Pin 1,3) and pin 2 (ground) , no results 
benchtested ECu ,. succes , k-line work great 

ecu in car , no cell 

REPLACED relay 100 , all others , 
checked all fuses 

confused , 

what about can-h Can-L lines ? what can cause the check engine light to refuse to get on when key is to on position ? ,


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## jeffpepin (Apr 12, 2015)

did you tryed to scan other adress than 01 ? in vag-com ? 

the 46 (comfort module) resulted garbage identification in my case , i removed then inspected it , no visual signs of damage ,, kindA Funny to have a non starting jetta , , we have the most low mile per gallon car in the whole world now  :laugh:


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## Martin_s1 (May 16, 2016)

*Same Problem!*

im having the same exact issue on my 01 wolfsburg edition, i cant pull any codes because the ecm isnt communicating with anything... no cel light on dash when key is turned to "on" position every other light comes on, tried replacing fuel pump,relays,fuses,cps and still nothing i get fuel to the injectors and i hear the fuel pump prime but i have no spark. i have voltage to the ecm harness. it just cranks and cranks but wont turn over and i have a stock radio. another thing is my rpm dont move either as im trying to crank. if any of you can help that would be great or get in contact through instagram at "martin_s1" just dm me or something thanks!


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## hUr (Jul 13, 2016)

Im having the same exact issue!

When I go to start my car, no CEL flashes. The car will crank and not start. Plus no communication with the ECM on VCDS. I can see all the other modules but the ECM. Also, tried swapping out the ECM, and still the same issue!

I have no idea what the problem is or how to fix this. Did anyone come up with a solution yet?


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## sammylees69 (Aug 9, 2016)

I am having the same problem no cel although it did not illuminate when the car ran and no spark and no fuel no comunication changed out ecu still no communication any one find our any thing

Sent from my SM-G900V using Tapatalk


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## sammylees69 (Aug 9, 2016)

hUr said:


> Im having the same exact issue!
> 
> When I go to start my car, no CEL flashes. The car will crank and not start. Plus no communication with the ECM on VCDS. I can see all the other modules but the ECM. Also, tried swapping out the ECM, and still the same issue!
> 
> I have no idea what the problem is or how to fix this. Did anyone come up with a solution yet?


U have any luck

Sent from my SM-G900V using Tapatalk


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## BudgetBuilt (Dec 15, 2016)

Sooooo out of anyone here has no one fixed their car... I'd love to know what your spacific issue was.


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## devinsinha (Mar 26, 2014)

I too have the exact issues that everyone has stated here and have checked everything y'all have said to no avail


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## 4no (Jun 30, 2009)

I had all the same symptoms. Took me over 2 months of tinkering on my spare time (good thing this isn't my daily) to find out the issue.

In my case it turned out to be 2 bad solder joints in my (soldered-in) chipped ECU. I resoldered all the connections and it fixed my issue.



https://photos.app.goo.gl/NxJsfzcicz1537WXA


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## Aubrey vw (Jan 4, 2022)

Did you ever find the issue?


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