B5 wont start wont connect to Vag Com or generic OBD scanner

[Ak303]

Never had an issue starting the car but recently had to replace the cam chain tensioner on my 1.8t B5 manual. Timed it and fired it up first try.

Came back to it the next morning and now it wont start. Also, wont connect to Vag or an OBD.

I've swapped relays, purchased a replacement ECU, checked all the fuses, checked and charged battery....after doing some research I see it could be the ABS module or possibly the K wire.

Just wanted to see if there was anyone who has come across this issue or had any other advice. Would prefer to narrow down the guessing game if possible.

Thanks in advance!

[LA4]

ABS module shouldn't stop the car from starting.

What happens when you turn the key? Does it even crank or is it a completely dead "click"?

[b5v6]

Does it have the appearance of a completely dead battery? My first thought is bad ground or some type of open in the power wires


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[Ak303]

It cranks and sounds like it wants to start. Battery tested fine but I charged it up anyway. Cranks and cranks.....

Want to say its not getting fuel but the pump is priming, Ive swapped out the fuel pump relay, swapped ECU, swapped crankshaft sensor....Ive checked all the fuses.

I dont think the ABS module would stop the car from starting. I did read that it could be a reason why I cant scan the car.

Already thrown a few easy possible easy fixes out there and have a few other ideas. Just curious if anyone has come across this issue or had any ideas.

[b5v6]

Hmmm, and you just did cam chain tensioner? Will turn over and never start if you lost compression due to timing failure


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[Ak303]

Just timed it with a certified VW mechanic after replacement. Tried a few things and called it a night. Unfortunately for me(good for him) he just had another baby and wont have time to come over for a while which is understandable.

Even with a timing failure, how would that affect the diagnostic port?

[b5v6]

I’m at a loss. Maybe something in the wiring around the area you were working was pinched creating a short. Not sure what direction to go in. Good luck!


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[Ak303]

Me too. Was hoping for advice so I dont keep throwing parts against the wall.

[OverSpun]

Check fuses for OBD II to see. Mine sometimes has strange connection but I just turn the key off and back into electric and it works again.

[Bdkxracer17]

Like everyone else said check the wires because the coil wires are back behind the valve cover and could of pinched and shorted them to ground. Doubtful since it did start but you never know

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[Ak303]

Ive checked all the fuses in the left dash panel. Ill try replacing the diagnostics fuse and disconnecting the ABS module next.

[Ak303]

Like everyone else said check the wires because the coil wires are back behind the valve cover and could of pinched and shorted them to ground. Doubtful since it did start but you never know

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Ill check the valve cover and see if anything looks out of ordinary.

[Ak303]

Like everyone else said check the wires because the coil wires are back behind the valve cover and could of pinched and shorted them to ground. Doubtful since it did start but you never know

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Checked the wires and nothing was pinched.

[Ak303]

Check fuses for OBD II to see. Mine sometimes has strange connection but I just turn the key off and back into electric and it works again.

Ive previously checked all the fuses. Rechecked them today, everything looked normal.

Tried to scan again, same deal.

Unplugged the ABS sensor, scanned and nothing.

Pulled the radio fuse, scanned and nothing.

Ordered the radio pins so I can pull the radio and see if the fuse on the back is blown.

[Ak303]

Took a while but I got the pins.

Prior to leaving town(10am Saturday) for Easter weekend I pulled the radio and 7,5(brown) fuse was blown. Returned 11pm Monday night. Gonna spend Tuesday on it and see what I can find.

[walky_talky20]

Are you getting spark? Assuming you are not getting spark:

#1 - I would check to see if you are actually getting power (DURING starter cranking) at the Coil Packs pin #1 (Red/Green wire).
#2 - If you are not getting power to the coil packs on pin #1 during cranking, I would then check if you are getting power to fuse #29 during cranking.

(If #2 is easier for you to check on your own, go ahead and do that first)

If you are not getting power at fuse #29 during cranking (and the fuse is not blown), I think you may have a faulty ECU Power Supply Relay. That relay (located next to the ECU) is responsible for powering 2 fuses:
- Fuse 29 (20 Amp in the side fuse panel) that drives the coil packs
- Fuse 204 (15 Amp in the ECU chamber) that drives the Cam Chain Tensioner solenoid

This relay can fail suddenly and without warning. When failed they generally just fail to initially engage - they usually won't cut out while you're driving. Sometimes you can just tap on the relay and get it to work for a few more drives, but it's kind hard to get at.

[Ak303]

Appreciate the info. I have previously swapped out both relays AND the computer in the ECU box. Relays were the first thing I tried.

Unfortunately, I didnt get a chance to look around this afternoon. I'm hoping once I get a new radio fuse in there it will at least allow me to scan and diagnose? I was actually really happy when I saw that the fuse was blown. Theoretically, it should lead me in the right direction.

I will double check those fuses once I swap the radio.

Are you getting spark? Assuming you are not getting spark:

#1 - I would check to see if you are actually getting power (DURING starter cranking) at the Coil Packs pin #1 (Red/Green wire).
#2 - If you are not getting power to the coil packs on pin #1 during cranking, I would then check if you are getting power to fuse #29 during cranking.

(If #2 is easier for you to check on your own, go ahead and do that first)

If you are not getting power at fuse #29 during cranking (and the fuse is not blown), I think you may have a faulty ECU Power Supply Relay. That relay (located next to the ECU) is responsible for powering 2 fuses:
- Fuse 29 (20 Amp in the side fuse panel) that drives the coil packs
- Fuse 204 (15 Amp in the ECU chamber) that drives the Cam Chain Tensioner solenoid

This relay can fail suddenly and without warning. When failed they generally just fail to initially engage - they usually won't cut out while you're driving. Sometimes you can just tap on the relay and get it to work for a few more drives, but it's kind hard to get at.

[walky_talky20]

- I would definitely see if you have spark or not. That's an easy check that will tell us a lot of information.
- Also, do you have a Check Engine Light coming on with Key On?

If it isn't the ECU Power Supply Relay, I'm thinking the ECU might not be powering up.
- Check all necessary power and ground to ECU, especially ECU pin 3 (Key Run/Start power via 10 Amp Fuse #7) and pin 62 (battery power, unfused).
- Check to see if your ECU Power Supply Relay is energizing with key On. If not, maybe find out why (ie: missing power, missing ground trigger, done broke, etc.)

Also, these are just internet armchair suggestions. So, certainly heed my signature and feel free to just "k thanks" and do your own thing.

[Ak303]

Put a new fuse in the radio this evening. Radio turned on, still could not connect to the diagnostic port. Now Im confused.

Will check out your suggestions and get back.

- I would definitely see if you have spark or not. That's an easy check that will tell us a lot of information.
- Also, do you have a Check Engine Light coming on with Key On?

If it isn't the ECU Power Supply Relay, I'm thinking the ECU might not be powering up.
- Check all necessary power and ground to ECU, especially ECU pin 3 (Key Run/Start power via 10 Amp Fuse #7) and pin 62 (battery power, unfused).
- Check to see if your ECU Power Supply Relay is energizing with key On. If not, maybe find out why (ie: missing power, missing ground trigger, done broke, etc.)

Also, these are just internet armchair suggestions. So, certainly heed my signature and feel free to just "k thanks" and do your own thing.

[Ak303]

- I would definitely see if you have spark or not. That's an easy check that will tell us a lot of information.
- Also, do you have a Check Engine Light coming on with Key On?

If it isn't the ECU Power Supply Relay, I'm thinking the ECU might not be powering up.
- Check all necessary power and ground to ECU, especially ECU pin 3 (Key Run/Start power via 10 Amp Fuse #7) and pin 62 (battery power, unfused).
- Check to see if your ECU Power Supply Relay is energizing with key On. If not, maybe find out why (ie: missing power, missing ground trigger, done broke, etc.)

Also, these are just internet armchair suggestions. So, certainly heed my signature and feel free to just "k thanks" and do your own thing.

No spark. For the hell of it I put new plugs in just in case. Didnt help. Pulled and tested the relays in the ECU box, everything was fine. Havent had time to play with it in the past week other than that.

Still wondering why I cant connect to the diagnostics port.

[xdewaynex]

Unplug the abs module under the hood and try connecting to the obd port. Mine has been disconnected for years, even clipped the k line wire from the radio harness because of aftermarket radio and Ive not had any trouble except for a blown fuse one time.

[walky_talky20]

No spark and no ECU communication. Sounds like ECU is dead or not getting power.

- Do you have the Check Engine Light illuminated with Key on?
- Did you check Fuse #7 / ECU Pin 3?
- Did you check ECU pin 62?

[Ak303]

Unplug the abs module under the hood and try connecting to the obd port. Mine has been disconnected for years, even clipped the k line wire from the radio harness because of aftermarket radio and Ive not had any trouble except for a blown fuse one time.

I did try that. Prior to finding the blown kwire fuse, and after.

[Ak303]

No spark and no ECU communication. Sounds like ECU is dead or not getting power.

- Do you have the Check Engine Light illuminated with Key on?
- Did you check Fuse #7 / ECU Pin 3?
- Did you check ECU pin 62?

I dont see CEL illuminated with key on but will definitely double check.

-Tried swapping with another ECU. Same thing. Cranks and sounds great but wont turn over.
-I check all the fuses multiple times but will check #7.
-No I havent Checked Pin 3 or 62.

Thanks, I have all weekend off and will see what I can come up with.

[Ak303]

Unplug the abs module under the hood and try connecting to the obd port. Mine has been disconnected for years, even clipped the k line wire from the radio harness because of aftermarket radio and Ive not had any trouble except for a blown fuse one time.

Bump.

[Ak303]

No spark and no ECU communication. Sounds like ECU is dead or not getting power.

- Do you have the Check Engine Light illuminated with Key on?
- Did you check Fuse #7 / ECU Pin 3?
- Did you check ECU pin 62?

It was fuse 7. Thank You walky_talky20
Replaced and car fired right up. Diagnostics works as well.

A true learning experience, I really hope this helps someone in the future.

[walky_talky20]

Yep. Power and ground are pretty important! Glad you got it running again. And thanks for posting the solution.

[HUFset]

If the k-line from the radio is crossed incorrectly, say you installed an aftermarket radio and incorrectly sent power to the k-line, it will disable your obd2 port. I'm pretty sure you have a BOSE symphony, so I doubt that was disabling it. Listen to Walky he is the electrical wizard.

EDIT: I see he helped you out.

[Ak303]

Yep. Power and ground are pretty important! Glad you got it running again. And thanks for posting the solution.

Indeed.

I just never would have guessed the Anti-Lock Brake System fuse controlled so much. I had previously checked all the fuses but the break was so small I must have just missed it.

[walky_talky20]

This is a good reason to check fuses with a test light. Once in a while you can even get a fuse that looks fine, but is actually open. So you just turn the key on and just run through each fuse with a test light and make sure there is power on both sides. Just tap each contact. It's much quicker, too.

[Ak303]

This is a good reason to check fuses with a test light. Once in a while you can even get a fuse that looks fine, but is actually open. So you just turn the key on and just run through each fuse with a test light and make sure there is power on both sides. Just tap each contact. It's much quicker, too.

Appreciate it. Im learning and collecting tools as I go!