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

BlueStreakTDI

Well-known member
Joined
Oct 11, 2002
Location
Southern, WV
TDI
Jetta, 2001 TDI, Silver, 5 speed ALH
Hi all.

I'm having a gremlin situation here. My 2001 Jetta TDI was starting fine when I parked it in the garage. I returned from a 5 month work assignment and now It will crank fine but won't start. Battery is new and in good condition. When the ignition switch is turned on the glow plug light does not ever illuminate.
Things I checked so far.

- All fuses including main ones on top of battery
- Glow plug resistance, all are .8 or .9 Ohms
- Removed glow plug relay and bench tested. (Applied 12v and got good continuity between contacts) Looks like there might be a timer circuit in there as well but don't know how to test that. Reinstalled relay and can hear it click when key is cycled.
- unplugged coolant temp sensor and checked to see if 12v was getting to glow plug harness when key is turned on. Not getting 12v power to glow plugs. (only get .01 volt change when key is cycled.) Could this still be a bad glow plug relay? (Relay 109)

Next step will be to check if glow plug power is getting to the relay socket, and check for continuity from relay socket to glow plug harness but I suspect all that is ok.
It's my understanding that the ECM won't allow the engine to start when the glow plug circuit is not working.

The other issue i'm having is that I now can not get VCDS to talk to the ECM. I'm using the same setup as I did 6 months ago and everything worked fine. (I was able to access ECM with VCDS) I'm getting a "too many communications errors to continue" message. I can access some other controllers with my VCDS so I don't think it is an issue with my computer or hex com interface cable. Could there be a problem with my ECM or Instrument cluster?

Any ideas on where to go next?
Thanks!
 

BlueStreakTDI

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Joined
Oct 11, 2002
Location
Southern, WV
TDI
Jetta, 2001 TDI, Silver, 5 speed ALH
No, CEL doesn't Illuminate at all. I tested relay 109 and it was pulling the contacts together but I suppose the other part of the relay could be bad.
 

jetta 97

Vendor
Joined
Dec 25, 2008
Location
Dallas (McKinney) ,TX ,USA
TDI
2 X Jatta MK5 2006
109 Relay is most common problem in this situation, I would go with that first , not to expansive.
My suggestion is buy one form Dealer, There is some OEM but I have seen those fail in some time. One form dealer it can go other 10 years.
 

Mozambiquer

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Mar 21, 2015
Location
Versailles Missouri
TDI
2004 VW Touareg V10 TDI, 2012 Audi Q7 V6 TDI, 1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
I would second that, relay 109 is a common issue, especially if it's actually activating when you turn the key on.
Get an oem one. I had an aftermarket one fail quote quite quickly...
 

Vince Waldon

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Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
No glowplug light and no communication with the ECU are two strong pointers that the ECU is not getting power. If not Relay 109 could be the ECU fuse.

The glowplug light itself is *not* directly related to the glowplugs getting power, oddly enough. :)
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
I tested relay 109 and it was pulling the contacts together but I suppose the other part of the relay could be bad.
Just as a datapoint: typically the 109 relay failures are related to the solder connection(s) between the relay contacts and the PCB, as opposed to the contacts themselves. So, still a suspect!
 

BlueStreakTDI

Well-known member
Joined
Oct 11, 2002
Location
Southern, WV
TDI
Jetta, 2001 TDI, Silver, 5 speed ALH
I've got a 109 Relay on the way. I'll let ya know how things work out.
Thanks to all who posted (y)
 

BlueStreakTDI

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Joined
Oct 11, 2002
Location
Southern, WV
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Jetta, 2001 TDI, Silver, 5 speed ALH
Okay, No luck with the new relay 109. It came today and I popped it in and everything is exactly the same. I think the ECU isn't getting power still. Have to start checking wires. Could a faulty instrument cluster be at play?

I'm up for pointers before I go digging into wiring harnesses.
 

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
Have you checked the fuse(s) as mentioned by Vince in post #6?
Hopefully it's that simple. Any evidence of rodents getting at the wires, especially those under the windshield rain tray?
 

BlueStreakTDI

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Joined
Oct 11, 2002
Location
Southern, WV
TDI
Jetta, 2001 TDI, Silver, 5 speed ALH
All fuses have been checked, twice now. I took them all out, tested and cleaned the spade contacts on them all, and reinstalled. They all checked good and still no glow plug light or MIL light when key is turned on.

I also tested for 12v power going into the relay panel - that checked good. I have 12v at the power supply relay 109 socket-pin 30 and I have 12v at the glow plug relay (180) socket-pin 2. So I'll say that both of those relays have power coming in to them.

I guess I'm going to try to get at the ECM connector and check pin 18 for power. That looks like that's where power comes in from relay 109.

What role does the instrument cluster play in this scenario? If it is faulty will it cause a crank, but no start condition?
 

Vince Waldon

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Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
I guess I'm going to try to get at the ECM connector and check pin 18 for power. That looks like that's where power comes in from relay 109.
I think that's your best bet... all signs point to "No power to the ECU", but you've eliminated all the normal causes for this. Checking directly and this point sounds like a good next step... weird one for sure.
 

BlueStreakTDI

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Joined
Oct 11, 2002
Location
Southern, WV
TDI
Jetta, 2001 TDI, Silver, 5 speed ALH
Ok, I have +12v on pin 18 of the ECM connector, so that is getting power. Hopefully the ECM isnt bad. I haven't found any chewed wires so far. This is turning into a real head scratcher.

Does anyone know the path that actually makes the glow plug light come on when the key is turned to the on position? I'm not seeing the glow plug light or check engine light at all when I turn on the key.
 

Mozambiquer

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Mar 21, 2015
Location
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TDI
2004 VW Touareg V10 TDI, 2012 Audi Q7 V6 TDI, 1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
Ok, I have +12v on pin 18 of the ECM connector, so that is getting power. Hopefully the ECM isnt bad. I haven't found any chewed wires so far. This is turning into a real head scratcher.

Does anyone know the path that actually makes the glow plug light come on when the key is turned to the on position? I'm not seeing the glow plug light or check engine light at all when I turn on the key.
Does the ecm have ground though? Also, did you load test the power? Simplest way to do that is get a cheap headlight bulb and use that as your load. I load test powers and grounds to the module I'm trying to diagnose. You can have 12 volts that cuts out when you have a load.
 

csstevej

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north nj
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2001 golf tdi 4 door auto now a manual, mine, 2000 golf 2 door M/T son's,daughters 98 NB non-TDI 2.0, 2003 TDI NB for next daughter, head repaired and on road,glutton for punishment got another tdi 2001NB,another yellow tdi NB , added an 06 NB DSG
I’m wondering if you have a flaky ignition switch.....cheap to change out......
 

wonneber

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Oct 12, 2011
Location
Monroe, NY, USA
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2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Check fuses 32, 34, and 43 for power. (not just looking at)
Also the big fuse 176 in the fuse box above the battery.
Its 110 amps.
 

greengeeker

Vendor
Joined
Feb 8, 2006
Location
Cambridge, MN
TDI
2002 Jetta GLS
Ignition switch provides 12v to fuse 29.

This goes to pin T121/37 of the ecu.

Ecu then send ground signal from T121/18 to the 109 relay.

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

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

HTH.

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

BlueStreakTDI

Well-known member
Joined
Oct 11, 2002
Location
Southern, WV
TDI
Jetta, 2001 TDI, Silver, 5 speed ALH
Ignition switch provides 12v to fuse 29.

This goes to pin T121/37 of the ecu.

Ecu then send ground signal from T121/18 to the 109 relay.

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

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

HTH.

Start at fuse 29. If that's not getting power, go to the ignition switch.
Thank you, I was looking for some confirmation that I was on the right track with the wiring diagrams for the ECU connector pins. I'll check it out today.
 

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
Ignition switch provides 12v to fuse 29.

This goes to pin T121/37 of the ecu.

Ecu then send ground signal from T121/18 to the 109 relay.

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

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

HTH.

Start at fuse 29. If that's not getting power, go to the ignition switch.
Nick, when you list T121/4&5 (example) do you mean pin T121, 4, 5 or T121, 124, 125??
Sorry for apparent ignorance. Just making sure. I may have some wiring issue chasing to do in my gasser/TDI swap erratically getting GP power.
Thanks!!
 

greengeeker

Vendor
Joined
Feb 8, 2006
Location
Cambridge, MN
TDI
2002 Jetta GLS
Nick, when you list T121/4&5 (example) do you mean pin T121, 4, 5 or T121, 124, 125??
Sorry for apparent ignorance. Just making sure. I may have some wiring issue chasing to do in my gasser/TDI swap erratically getting GP power.
Thanks!!
Hey Marc,
Just adhering to format in the wiring diagrams - they denote the connector first, then the pins. I should have said: T121/4 & T121/5.

Careful - on the last gasser>TDI swap I did I had to do some fuse rewiring to connect them to the correct function of the ignition switch (D/15 vs D/86 vs D/x).
 

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
Hey Marc,
Just adhering to format in the wiring diagrams - they denote the connector first, then the pins. I should have said: T121/4 & T121/5.

Careful - on the last gasser>TDI swap I did I had to do some fuse rewiring to connect them to the correct function of the ignition switch (D/15 vs D/86 vs D/x).
Ahhh, yes I recall those designations now. Been a long time.
I don't use the converted/swap car (2003 1.8T Jetta from 2003 TDI Jetta) after they start salting the roads, so not much cold weather use but still need pre-glow spring and fall sometimes.
I will have to touch bases with you when I get back to using it and provide the wiring I followed. Sometimes (most of the time) it throws a code (3 or 4 codes for GP) other times nothing. Quite erratic. Everything else works.
Thanks and sorry to take the thread a bit off track.
 

quartersaw

Veteran Member
Joined
Sep 20, 2005
Location
Albany, NY
TDI
2002 Jetta Wagon, '96 B4V,'99 2 door Golf
Okay, No luck with the new relay 109. It came today and I popped it in and everything is exactly the same. I think the ECU isn't getting power still. Have to start checking wires. Could a faulty instrument cluster be at play?

I'm up for pointers before I go digging into wiring harnesses.
...Might sound crazy, but check the wires @ the Starter
 

BlueStreakTDI

Well-known member
Joined
Oct 11, 2002
Location
Southern, WV
TDI
Jetta, 2001 TDI, Silver, 5 speed ALH
...Might sound crazy, but check the wires @ the Starter
All starter wires look good. Removed wires from terminals and cleaned everything anyway.
I also checked resistance on ground connections under the battery. All checked good, but I took everything apart and cleaned it up while I was in there.
 
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