Frequency of faulty NEW engine rpm speed sensor G28 ?

[Tony Hoffman]

They are functionally identical. You hit the nail on the head, only
the connectors are different, and only in color.

No, there definately should NOT be an open circuit. As you said, the
coil of wire has a set resistance. It makes no difference if its
mounted or not. So, either your meter is set wrong (as mentioned) or
in fact the new sensor is bad. I've never had a new one come in bad.
Probably changed 10 or so.

BTW, if you swap the connector position, you also have to swap the
positions of them. One reads a pin and the other reads all the teeth
on the flywheel.

The car needs both to start, but only one of them to stay running. I
don't remember which is which.

Tony

On Mon, Nov 22, 2010 at 3:29 PM, Jim Hollander at Hot Grips Mfg., Inc.
<Jim at hotgrips.com> wrote:
> My Vag-Com identified a faulty engine rpm sensor G28 on my '91 200 TQ 20v so
> I ordered a new one.  Bentley Manual advised to check that ohms between
> terminal 1 and 2 be approximately 1000 ohms, with terminals 1-3 at open
> circuit, and 2-3 open circuit as well.  When I got the G28 sensor I was
> curious and checked the new one with my ohm-meter and the reading on all
> combinations between the 3 terminals was an open circuit.  I wondered if the
> reason there was no ohms reading between terminals 1 and 2  might be because
> the sensor needed to be positioned over the flywheel teeth to get a correct
> reading.  But if there is a coil inside the sensor shouldn't there be
> approx. 25 ohms at all times regardless of proximity to flywheel teeth?
>
> I installed the sensor, and the reading did not change once it was in proper
> position.  I plugged in the Vag-Com and still the code showed a engine rpm
> sensor with no signal (bad sensor).
>
> What is the frequency of a new G28 sensor being bad, any feel for this...
> anyone?
>
> My other question is:  There are two sensors (G28 and G4) on that aluminum
> cast bracket that sits above the flywheel teeth.  Is the only difference
> between them the color of the connector being tan or black, with their size
> and ohms, functionality being identical otherwise?  In other words, if I
> kept track of the connectors, can they be interchangeable?
>
> Removing the old engine rpm speed sensor G28 was no picnic, and a bit of
> abuse befell the other sensor  G4 (black wire end connector at the bracket
> behind the engine on the firewall) next to it, because after installing the
> new (bad) engine rpm speed sensor G28 my Vag-Com now showed both a bad
> engine rpm sensor G28 and a bad ignition timing sensor G4 too.
>
> It was very discouraging going from one a bad G28 to a bad G28 AND a bad G4
> sensor.  But if these G28 NEW sensors often come in bad, then it all makes
> sense.  Should I just order another G28 and insist on checking the ohms
> between terminals 1 and 2 at the parts counter before accepting it? Of
> course I will bring a copy of Bentley page 28.41 where the 1000 ohm test is
> described.
>
> Jim