Date: Sat, 17 Oct 2009 16:20:29 -0700
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: Jetta swap: Check Engine Light Install Electrical Questions
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re
"No continuity is shown between new wire from
> ECU and vehicle ground ign. on or off. "
if you actually mean what you have written there, you don't understand the
circuit.
The ecu SUPPLIES ground to the 'ground side' of the CEL.
Switching can take place in either the ground side, or power side of any DC
circuit - this is an example of switching in the ground side.
The LED for the CEL has power on one side. As long as polarity is observed,
if the other side 'sees' ground........
the light will be turned on.
The ecu is what SUPPLIES this ground signal.
at no time is there any connection between that ecu pin and chassis ground.
One could say you are trying to make this too hard.
re
Should I test continuity between new wire "harness ground"?
no no no no no .
look at it this way.
pretend there is a tiny switch ( there is, but it's solid state ) inside the
ECU.
the body of the ECU is grounded to the van's body.
if anything , you'd check that the ecu's ground has continuity with the body
of the van, which is sure has to have, or it couldn't work.
So when that little switch 'closes' ........
it PROVIDES a ground path for the LED, turning it on.
Cant' say it any simpler than that.
that wire........which in my opinion you should never check that it is
conencted to ground, EXCEPT , by observing that it turns on an LED (
incandesent will work too, but it expects to see an LED ) only is ground,
when the ECU switches it to ground inside the ECU.
if it supplies a ground, that turns on the LED, you're done. Like if you
turn on the key, the LED is on, you fire up the engine ( with no codes
present ) and it goes out, 'YD' - you're done.
or.........when codes are pressent to turn on the LED ..it should be one.
But don't do anything with or to that wire other than connect it to an LED
properly, with correct polarity.
please, pleasse please......
re
but then why do I see
> 12.xx volts with ign. off?
don't do that !
this is akin to asking ..........., well, can't think of a good enough
example..............but by doing that .you are looking for the wrong thing
at the wrong time in the wrong place with the wrong method.
we don't know what the engineers had in mind or what they did.
All we can do is check that things work like we understand them to work.
like test for what we know should be there, and 'don't make things up.'
I don't think it says anywhere in any troubleshooting or Bently book to look
for voltage on the ECU CEL pin with the key off.
Then why do that ?????????????????????
mercury must be retrograde of something ! Yikes !
and I think Batt + power on the 'other side' of the LED is the real right
way, not ign power. As I said, all soobies are that way.
I can well imagine that it's not clear in Bentley for your year engine
though.
smiles, Scott
----- Original Message -----
From: "neil n" <musomuso@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, October 16, 2009 3:28 PM
Subject: Jetta swap: Check Engine Light Install Electrical Questions
> Well I've been melting my head staring at diagrams/reading, and just
> don't get it.
>
> The new CEL works. Checking OBD, it blinks. Key at 15: CEL on. Engine
> running: CEL off. CEL wire wasn't present at ECU connector from
> factory. I re-routed an unused ECU wire (68/51 lilac/white) to CEL pin
> (68/5) . (*how I did it. )
>
> Though it works I'm concerned because......
>
> Ign. on or off, VOM see's 12.xx volts between B+ (30) and new wire
> (ground) from ECU. But. No continuity is shown between new wire from
> ECU and vehicle ground ign. on or off. I found this out by checking
> things before running the new wire.
>
> Should I test continuity between new wire "harness ground"? Still,
> IIRC, all wiring harness grounds eventually connect to the frame.
> Maybe the ECU ground is switched on/off by ECU, but then why do I see
> 12.xx volts with ign. off?
>
> Positive connection to new CEL light is wired to 15. Is this correct?
>
> I appreciate any help. The light works, but I'm concerned I might fry
> the ECU over the long haul due to a minute wiring flaw. The ground
> weirdness and lack of instrument cluster wiring detail (maybe an
> electrical component crucial to proper operation of new CEL is
> missing?) are prompting me to triple check my work.
>
>
> Neil.
>
>
> * Located ECU wire 68/51 in Jetta diagram. Physically confirmed pin
> location at ECU connector. Grounded other end of wire to frame and
> checked continuity. I didn't check to see if it spliced off anywhere
> to + within the Jetta harness as this wasn't shown in the diagram. I
> have no idea what this wire was for, but AFAIK, it connected to the
> Jetta instrument cluster which I'm not using.
>
> --
> Neil Nicholson '81 VanaJetta 2.0 "Jaco"
>
> http://tubaneil.googlepages.com/
>
> http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines
