Having problems with the immobiliser on a Mk 4 Golf. When I put the
ignition key in it doesn't always turn off the immobiliser so you can't
start the engine. Under these conditions the immobiliser light is
flashing. Same with both keys.

Sometimes it takes upwards of 10 tries before it works. Usually at the
most inconvenient times.

Had this problem for several years and it happens maybe once a month.
But this year it seems worse. I've read all the stuff on the internet
about this, and it seems hard to get a resolution with such an
intermittent fault.

Over the winter I noticed that the battery is getting a bit tired and
it'll need a new one shortly. Never seen it mentioned, but I'm
wondering if the two things are related. I've heard of similar problems
with other makes.

Theory is that if the battery volts are a bit low then the signal picked
up by the coil in the ignition switch is weaker, and it falls below a
threshold somewhere i.e. poor design.

Is this credible?

On 16/08/2010 10:18, nick wrote:
Having problems with the immobiliser on a Mk 4 Golf. When I put the
ignition key in it doesn't always turn off the immobiliser so you can't
start the engine. Under these conditions the immobiliser light is
flashing. Same with both keys.

Sometimes it takes upwards of 10 tries before it works. Usually at the
most inconvenient times.

Had this problem for several years and it happens maybe once a month.
But this year it seems worse. I've read all the stuff on the internet
about this, and it seems hard to get a resolution with such an
intermittent fault.

Over the winter I noticed that the battery is getting a bit tired and
it'll need a new one shortly. Never seen it mentioned, but I'm wondering
if the two things are related. I've heard of similar problems with other
makes.

Theory is that if the battery volts are a bit low then the signal picked
up by the coil in the ignition switch is weaker, and it falls below a
threshold somewhere i.e. poor design.

Is this credible?


The most likely problem is the pickup coil that is around the ignition
lock (a fairly common problem), or a dodgy key (try a spare if you have
one).

On 16/08/10 12:20, Chris Bartram wrote:
On 16/08/2010 10:18, nick wrote:
Having problems with the immobiliser on a Mk 4 Golf. When I put the
ignition key in it doesn't always turn off the immobiliser so you can't
start the engine. Under these conditions the immobiliser light is
flashing. Same with both keys.

Sometimes it takes upwards of 10 tries before it works. Usually at the
most inconvenient times.

Had this problem for several years and it happens maybe once a month.
But this year it seems worse. I've read all the stuff on the internet
about this, and it seems hard to get a resolution with such an
intermittent fault.

Over the winter I noticed that the battery is getting a bit tired and
it'll need a new one shortly. Never seen it mentioned, but I'm wondering
if the two things are related. I've heard of similar problems with other
makes.

Theory is that if the battery volts are a bit low then the signal picked
up by the coil in the ignition switch is weaker, and it falls below a
threshold somewhere i.e. poor design.

Is this credible?


The most likely problem is the pickup coil that is around the ignition
lock (a fairly common problem), or a dodgy key (try a spare if you have
one).

Thanks for the prompt reply.

When it fails neither of the 2 keys I have will start the car. Then it
can go for weeks without a problem, with either key working fine.

Assuming both keys are OK then that would point to a problem from the
coil back in to the electronics.

You say the coil is a fairly common problem. So is it worth changing
the coil on spec?

Presumably you don't think my battery theory is credible?

On 16/08/2010 15:32, nick wrote:

You say the coil is a fairly common problem. So is it worth changing the
coil on spec?


It would be the first thing I'd try, but a scan with VCDS might help
diagnosing things.

Presumably you don't think my battery theory is credible?

It's possible I suppose, but I think if there's enough power to crank
the car then I'd expect there would be enough to raed the chip. Also, my
wife's Lupo had a weak battery last winter, and even if it was only just
cranking, the immobiliser didn't play up, so I doubt it's that marginal.


[edit]

Having googled it, your theory does hold water. Maybe you should change
the battery (as it's on it's way out) anyway and see if the problem goes
away. Chances are that battery will fail completely soon.

From http://www.myturbodiesel.com/1000q/m...-2-vw-audi.htm

General troubleshooting procedures

1. First, make sure the car battery is charged. A low battery can
cause problems with the immobilizer. It also results in low cranking
RPM during engine start - this will cause the ECU to prevent fueling.

2. Try another key - you should have a valet key and spare key that
also have an immobilizer chip in them. If they work, then you have
isolated the problem to the key. Again, there is NO battery for the
immo chip, it gets power from the ignition switch transmitter. You can
try reprogramming the chip with the procedures linked to below.

3. Check for error codes - scan the car with a VCDS to see if there is
a problem with the system and refer to the appropriate procedure below.

4. You can try just leaving the key in the ignition to "ON" but not
start for a few minutes. Many people report that the light just goes
away after 10 minutes as if nothing ever happened. This and the next
solution appear to have something to do with a capacitor discharge or
something resetting. It sounds strange but many report that it works.

5. Disconnect the battery negative terminal and step on the brake pedal
- this turns on the brake lights and discharges any stored electricity.
This may reset the immo system. I've heard that disconnecting BOTH
negative and positive terminals of the battery and then touching the
cables to each other only, while not attached to the battery can also
reset it. I think that it takes more time and does the same thing as
disconnecting the negative side and turning on the brake lights. Again,
don't touch the cables to the battery, touch them only to each other
while both are disconnected from the battery - you don't want to short
the battery out.

6. Check wiring and plugs at instrument cluster and pickup coil at the
ignition switch, there is a chance it could be faulty. You could try
wiggling the key in the slot in case there's a problem with the pickup
coil. However, the range of the antenna/chip is about 1" so it's
definitely not a range problem.

7. Put a trickle charger on the battery, put the key to the "ON"
position and leave it for a few hours. If it didn't reset after 10
minutes it's been known to reset after a few hours and never appear again.

On 16/08/10 16:18, Chris Bartram wrote:
On 16/08/2010 15:32, nick wrote:

You say the coil is a fairly common problem. So is it worth changing the
coil on spec?


It would be the first thing I'd try, but a scan with VCDS might help
diagnosing things.

Presumably you don't think my battery theory is credible?

It's possible I suppose, but I think if there's enough power to crank
the car then I'd expect there would be enough to raed the chip. Also, my
wife's Lupo had a weak battery last winter, and even if it was only just
cranking, the immobiliser didn't play up, so I doubt it's that marginal.


[edit]

Having googled it, your theory does hold water. Maybe you should change
the battery (as it's on it's way out) anyway and see if the problem goes
away. Chances are that battery will fail completely soon.

From http://www.myturbodiesel.com/1000q/m...-2-vw-audi.htm


What a great page. Never found it before. Will try a new battery
first, then a coil. Many thanks Chris.

Nick