No glow plug light, crank but no start. No VCDS communication wiith ECM

[BlueStreakTDI]

Ignition switch provides 12v to fuse 29. Checks Ok, 12.8v with Ignition On

This goes to pin T121/37 of the ecu. Checks Ok, 12.8v with Ignition On

Ecu then send ground signal from T121/18 to the 109 relay. Checks Ok, have good continuity from pin T121/18 to 109 relay socket terminal 9/85

109 relay then powers up fuses 32 (main ecu power, qa housing), 34 (solenoids, MAF, glow plug module), 43 (PCV heater, brake switch)

Checks Ok, all 3 fuses power up when ignition is turned on, this is a good sign the ECU is working as it is powering up the 109 relay and sending power to the 3 fuses.

Of course, none of this can happen if you don't have a good ground to the ecu (T121/4&5).

Checks Ok, T121/4 and T121/5 had continuity to ground but there was some resistance from the pin in the connector to the ground points I checked. I read 13 Ohms from each pin to the engine block, and 29 Ohms from each pin to the neg battery terminal. I don't consider that to be high resistance, just more than I expected. I cleaned up the grounds anyway. This didn't seem to affect the ECU from powering up as it is controlling the 109 relay as advertised.


HTH.

Start at fuse 29. If that's not getting power, go to the ignition switch. Checks Ok,

So far all the wiring I've looked at has been in very good shape for a 20 yr old car.

I'm going to pull the instrument cluster today and see what I can see in that area. All appears to be working there except the MIL (check engine) light and the glow plug light. Can anyone advise if there is a path through the instrument cluster that could cause this condition if there was a failure in that circuit.

This is turning into a real puzzle...

 

[greengeeker]

ECU power is not routed through the cluster. If you had immobilizer deleted, you could run with cluster removed. With immobilizer, should start and shutdown almost immediately.

Nice work! I suppose the last thing to do is verify the ECU is getting voltage, at the connector. Will get you those pins when I get home.

 

[Mozambiquer]

The other things to verify would be ground wires, and communication wires.

 

[BlueStreakTDI]

The other things to verify would be ground wires, and communication wires.

Do you know what pins the communication wires are on and an good way to check for signal. I can check for continuity from ECM to next point in the wiring diagram but It would be better If I could check if I was actually signals on the communication wires.

I have verified my ECM is controlling the 109 Relay and that in turn is powering fuses 32, 34, and 43. So at least part of the ECM is working. I agree it could be a communication problem as my VCDS will not connect to the ECM. With all that I've checked so far I'm still not getting the glow plug light or check engine light to come on when I turn the ignition on, so something isn't getting the input it needs to allow an engine start. I'm investigating deeper under the dash today.

Could a bad glow plug relay (180) be a cause of this problem? I would think I should still be able to access the engine control module with VCDS even if that relay is bad.

 

[Mozambiquer]

Do you know what pins the communication wires are on and an good way to check for signal. I can check for continuity from ECM to next point in the wiring diagram but It would be better If I could check if I was actually signals on the communication wires.

I have verified my ECM is controlling the 109 Relay and that in turn is powering fuses 32, 34, and 43. So at least part of the ECM is working. I agree it could be a communication problem as my VCDS will not connect to the ECM. With all that I've checked so far I'm still not getting the glow plug light or check engine light to come on when I turn the ignition on, so something isn't getting the input it needs to allow an engine start. I'm investigating deeper under the dash today.

Could a bad glow plug relay (180) be a cause of this problem? I would think I should still be able to access the engine control module with VCDS even if that relay is bad.

I'll look it up, but sometimes a separate module will take down the k-line communications, for example of it's shorted out. Can you connect to any of the other modules on the car?

 

[BlueStreakTDI]

I'll look it up, but sometimes a separate module will take down the k-line communications, for example of it's shorted out. Can you connect to any of the other modules on the car?

I can connect to ABS Brakes, Airbags, Steering Wheel, Instruments, CAN Gateway and Central Conv. modules. The Instrument and CAN Gateway modules both show a Fault 01314 'Engine Control Module 49-00 No Communications. I'm checking the ECM connector 121/5 for good ground, and I think 121/1 and 121/2 should be

 

[BlueStreakTDI]

Pins 121/1 and 121/2 should be +12v supply to ECM. If all that checks out I'm thinking its either a communication line problem or a bad ECM.

 

[Vince Waldon]

Yeah, man o man, I'm the guy usually saying the ECU is the most bullet-proof part of the car, but in this case if you've eliminated the obvious and the not-so-obvious... Would be great to track down an ECU to borrow, if just to see if you get a test fire (Car won't run more than 3-5 seconds with a borrowed ECU unless the IMMOB is re-configured to the new ECU).

 

[jettawreck]

If it wasn't so horribly cold (-27*F this morning) I would pull the ECU from my 2001 and send it for a test start. I haven't been using the TDI much at all this winter and it's been left outside. It's a good reminder, I need to put the charger on it. In a couple weeks it's warming up some near "average".
Elusive electrical issues are a big pain. Been following this one, hoping to see a resolution.

 

[BlueStreakTDI]

If it wasn't so horribly cold (-27*F this morning) I would pull the ECU from my 2001 and send it for a test start. I haven't been using the TDI much at all this winter and it's been left outside. It's a good reminder, I need to put the charger on it. In a couple weeks it's warming up some near "average".
Elusive electrical issues are a big pain. Been following this one, hoping to see a resolution.

Wow, that's cold! I'm going to do a couple more checks and if they are ok I think all signs are pointing to a bad ECM.

 

[BlueStreakTDI]

I have found a few used / verified working ECM's. I have VCDS, can I code a replacement ECM to my Jetta? How difficult is the process?
Note that with my current problem I cannot get VCDS to communicate with my current ECM. Not sure if info has to be copied off of old ECM to the replacement.

 

[BobnOH]

ECUs like to match by part no. car-part.com has decent prices. I'd rule out everything else before replacing that unit. There is no data you can upload from the old ECU via VCDS.

 

[Mozambiquer]

If you change the ecm, you would either have to immobilizer delete it or get the SKC which you can get with a really cool tool that one of the fellow club members made Free VDS PRO-VAG TACHO I used it to retreive the skc on my mk4, as well as my family's 3 and my b5.5 passat. You then have to adapt the ecm with vag-com.
Have you tried load testing the all the wires? A headlight bulb works great for that. The other thing would be to check for a short to ground in the com wires, and a short to the case in the com wires at the ecm. I had that on a TCM once, and basically had the same rigamarot that ypu are running through, except my passat would still run, since it was the TCM, just no communication. That indicated a failed TCM, though in my case i removed the case and that fixed it, but younprobably would not want to do that with an ecm.

 

[BlueStreakTDI]

If you change the ecm, you would either have to immobilizer delete it or get the SKC which you can get with a really cool tool that one of the fellow club members made Free VDS PRO-VAG TACHO I used it to retreive the skc on my mk4, as well as my family's 3 and my b5.5 passat. You then have to adapt the ecm with vag-com.
Have you tried load testing the all the wires? A headlight bulb works great for that. The other thing would be to check for a short to ground in the com wires, and a short to the case in the com wires at the ecm. I had that on a TCM once, and basically had the same rigamarot that ypu are running through, except my passat would still run, since it was the TCM, just no communication. That indicated a failed TCM, though in my case i removed the case and that fixed it, but younprobably would not want to do that with an ecm.

Yes, I have a similar light bulb set up for load testing. I'll take a look at the com wires. I'll check out the SKC tool too. thanks!

 

[BlueStreakTDI]

Well guys I'm pretty sure I have a bad ECM. This afternoon I did some more testing and the results seem to point to ECM trouble. I have verified the there is good grounds on ECM connector harness pins T121/4, T121/5. I also load tested these with a headlight bulb so we know they carry current. Next I checked pins 121/1, 121/2 for 12v with the connector plugged into the ECM and the ignition switch on. I had battery voltage at those pins, and load tested those as well so all is working as advertised there. Moving on I checked for continuity and shorts to ground on the communication wires. Data-BUS Can High and Low. CAN High went from T121/7 to Pin 19 on the green instrument cluster connector [32 pin] CAN Low went from T121/6 to pin 20 of the same connector. Both checked good on continuity and no shorts to ground. I load tested them with the light bulb as well. Then I moved on to check the pins on the ECM itself to see if there were any shorts to the case of the module. T121/6 and T121/7 chedked good with no shorts to the housing.
My thinking is the ECM is getting good ground and power, the comm lines check good and all the other wiring I encountered along the way looked good with no signs of chewing or corrosion etc. I'm going to get an ECM on the way and I'll let y'all know how it goes. Thanks for all of the suggestions!

 

[Mozambiquer]

Well guys I'm pretty sure I have a bad ECM. This afternoon I did some more testing and the results seem to point to ECM trouble. I have verified the there is good grounds on ECM connector harness pins T121/4, T121/5. I also load tested these with a headlight bulb so we know they carry current. Next I checked pins 121/1, 121/2 for 12v with the connector plugged into the ECM and the ignition switch on. I had battery voltage at those pins, and load tested those as well so all is working as advertised there. Moving on I checked for continuity and shorts to ground on the communication wires. Data-BUS Can High and Low. CAN High went from T121/7 to Pin 19 on the green instrument cluster connector [32 pin] CAN Low went from T121/6 to pin 20 of the same connector. Both checked good on continuity and no shorts to ground. I load tested them with the light bulb as well. Then I moved on to check the pins on the ECM itself to see if there were any shorts to the case of the module. T121/6 and T121/7 chedked good with no shorts to the housing.
My thinking is the ECM is getting good ground and power, the comm lines check good and all the other wiring I encountered along the way looked good with no signs of chewing or corrosion etc. I'm going to get an ECM on the way and I'll let y'all know how it goes. Thanks for all of the suggestions!

Sounds like a good time to do some upgrading... Like a tune with immobilizer delete, and simple fun stuff like that...

 

[BlueStreakTDI]

Used ECM is on the way. I think I can marry it to my Instrument cluster. I have VCDS and the scratch off SKC code for my car. I checked and I have IMMO-2 and according to the Ross-Tech wiki I should be able to marry the new ECU to my cluster. If anyone has a good write up for doing that I'm all ears.

My thinking is I'll get the car running with the used ECU and make sure that is the problem, then we can talk about a stage 2 tune

 

[BlueStreakTDI]

Problem Fixed!! The ECM was the culprit. I installed the used ECM and was able to marry it to the instrument cluster using VCDS. My car IMMO-2 so It was a simple process in VCDS - see the Ross-Tech wiki for the process.

Thanks to all who posted with help / suggestions!

 

[Mozambiquer]

Problem Fixed!! The ECM was the culprit. I installed the used ECM and was able to marry it to the instrument cluster using VCDS. My car IMMO-2 so It was a simple process in VCDS - see the Ross-Tech wiki for the process.

Thanks to all who posted with help / suggestions!

Great! Its kinda funny, this was a while back, but right now I have a car that's doing the exact thing, except it'll start and die, like the immobilizer is killing it. No connection with vcds, but I can access instruments, TCM (it's an auto) abs and etc. I put an immobilizer deleted ECM in and it fired right up and ran great, but still couldn't connect with Vagcom. I'm just going to delete the immobilizer in it's computer and send it.