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No Check Engine Light

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steve Y View Drop Down
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    Posted: 11 Aug 17 at 01:20
Hi
I have a 2006 2.5 TDI Transporter, had it since new.
I noticed awhile ago that the CEL does not light up when ignition turned on as it should.
Took the van to a vw specialist technician. They removed the instrument cluster and tested voltage inputs and said all OK Probably fault in cluster (LED or circuit fault)
I then sent cluster to a repairer, and they could not find a fault, and suggest ECM not sending signal.
The van runs perfectly, no fault codes show on scan.
If I do a self test of the instruments using VCDS scan it cycles through all cluster instuments, lights, beeps etc but no CEL. Should the CEL illuminate during this test?
If I run the van with the MAF sensor unplugged a fault shows up on the scan tool but the CEL doesn't illuminate. Should it?
I know the usual CEL problem is it coming on and staying on and some would love for it not to come on. However the van is deemed unroadworthy it CEL doesn't work
Any ideas of what I should do next?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug 17 at 20:46
It's not part of the instruments test, or at least it isn't on my '04. https://www.youtube.com/watch?v=dzLAGwMuDIg  Start at about 0.47 if you want avoid all the exciting needle sweeps. LOL   

(Btw, if anyone wants to hear what a failing T5 starter motor sounds like, watch/listen.)  Wink 

You need to find someone who can check the signals that should be present at the dash.  However since you have VCDS you could try deliberately introducing a fault by taking say, the MAF sensor plug off and driving just to see what happens when it is supposed to actually come on in anger. 

There was a good thread here about loom chaffing behind the dash, I think that was in relation to another fault but you never know.  It seems odd that you have no other symptoms which does sound more like a dash problem.  Did the dash firm confirm that the CEL was working on their test? 



Edited by T5 TDI - 12 Aug 17 at 20:48
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stryne Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 17 at 06:16
By "CEL" do you mean the glow plug 'coil' indicator, or the 'engine' symbol, obviously they each have different meanings, (sensor inputs, ecu outputs). But in any case it is difficult to determine from the wiring diagram how to simulate the light on, i.e. whether high or low signal, & low or high resistance signal. The 'coil' indicator could (I think?) be simulated with VCDS by operating the glow plugs. The 'engine' indicator might be more difficult, or can can VCDS operate or check the Lamda probe, EGR, dpf, etc. That wiring fault suggested by 'T5 TDI' might be as good as any place to start looking.

Just to add a bit more, if you know or find the pin-out of the instruments plugs, you could check the signal there by moving the instrument cluster out, but as always, get a trained technician if you are not sure.



Edited by Stryne - 13 Aug 17 at 06:28
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve Y Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug 17 at 00:30
Thanks for the replies
Stryne the light not coming on is the engine light not glow plugs
        I now dont think its part of the instrument test but I tried it anyway.
        I have run the van with MAF sensor unplugged and VCDS showed the fault
        but no engine light.
T5TDI    The VW techs said that the correct voltages were at the cluster but were
        a bit vague about what they were when I questioned them
        I suspect a faulty wire from ECM (if thats were the signal comes
          from)to the cluster. I cant find a wiring diagram to find which wire
        from the ECM or which pin at the cluster the signal travels .
        Any ideas re obtaining a wiring diag ?
       Maybe pull the dash out again and start looking for some chaffing of wires
     As I said originally van starts and runs perfectly
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug 17 at 11:05
It's worth checking all of the fuses however unlikely it sounds, especially no 8 and 22 in the fuse box in the cab.  But a test with a meter of all of the fuses including the ones down by the battery really is a must before you dismantle anything else.  

As I see it, the diagnostic system is on the CAN network and because of this it is in a way, connected to everything (certainly the engine controller, the convenience controller and the onboard voltage control unit.  So you can expect CAN wiring to go to the dash which should put the CEL on if a signal for a fault is received on the network.  The voltage that actually powers the CEL led may already be at the controller in the dash and you would need special equipment to be able to measure the digital can signals.    

You could try looking with VCDS at both the CAN gateway and the dash itself (which comes under 'Instruments') to see if any fault codes are there.  If you do a full scan with VCDS it should find the CAN gateway and the dash if you are not sure how to find them directly. But start with a careful check of those fuses using a meter or test lamp not just looking at them. Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stryne Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug 17 at 13:53
Yes, it appears information from the ecu to dash computing is all carried by the canetwork, (as I see it at the moment), checking continuity of the can cabling to the dash connectors might be in order, although you did mention the signals had been checked ?

T32 - 32 pin connector, blue     right, looking at rear of panel
T32/23 - Terminal 30, positive
T32/24 - Terminal 31, earth
T32/25 - Self-diagnosis/ K-wire
T32a - 32-pin connector, green     left, looking at rear of panel
T32a/4 - CAN
T32a/8 - CAN-H (convenience)
T32a/9 - CAN-L (convenience)
T32a/15 - CAN-H (info)
T32a/16 - CAN-L (info)
T32a/19 - CAN-H (drive train)
T32a/20 - CAN-L (drive train)
T32a/27 - CAN-H (out)
T32a/28 - CAN-L (out)
 the terminals are numbered on the plugs, a bit hard to make out, use a scope or a digital multimeter for measuring.
Hope this is not confusing.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve Y Quote  Post ReplyReply Direct Link To This Post Posted: 15 Aug 17 at 02:36
Thanks again for the information
I have checked the fuses visually will do a proper test
Have done a full scan with VCDS and no faults show anywhere
You are getting a bit technical for me Stryne I dont know about testing the CAN to dash I was told by the vw tecs that all correct signals were reaching the cluster
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stryne Quote  Post ReplyReply Direct Link To This Post Posted: 15 Aug 17 at 12:12
Well if they were correct then the cabling should be ok, and to me that would leave the dash controllers or the LED itself to be at fault, or maybe a dry soldered joint on a circuit board. Have a look at the pics in this thread to see what the dash insert looks like when out of the car, I would have liked more time when I had that out, to document lots more of it.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve Y Quote  Post ReplyReply Direct Link To This Post Posted: 22 hours 31 minutes ago at 02:08
Thanks Stryne
I have had the cluster out of van a couple of times. It was sent to a company Injectronics who do repairs, to check LED, Circuits etc They could not find a fault.
I disconnected the MAF sensor again and drove around all day A fault code showed on VCDS but no light on dash, but the van ran as good as ever !!!
I would have thought I would have noticed some change in performance.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 15 hours 14 minutes ago at 09:25
On mine it runs ok but slightly flat.  If you ever want to check the MAF you can easily check the the expected against the actual airflow either by data logging for later perusal/graphing or watch it live on VCDS by using Vagscope.  

It does look like the fault is within the cluster as long as there are no other problems with the dash and you have no communication or other faults showing in any other controller.  I suppose it could be an ECU fault but you would have thought it would have shown up on VCDS as a missing message on the can gateway or similar.  

I think you will have to ask them to check it again with particular reference to the check engine light.  Or at least ask if they are absolutely certain the cluster is 100% since you are going to be spending money based on their diagnosis.  

Currently the CEL being on isn't an MOT failure here in the UK, are you sure about the ausssie rules? ;-) 


Edited by T5 TDI - 15 hours 9 minutes ago at 09:30
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stryne Quote  Post ReplyReply Direct Link To This Post Posted: 10 hours 48 minutes ago at 13:51
@T5 TDI, when your MAF is disconnected, which dash warning shows ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 10 hours 4 minutes ago at 14:35
I haven't done it for years but it's only ever the check engine light.  As far as I know the glow plug light only ever comes on (as an engine management light) if the brake pedal switch is faulty.  
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