Engine speed sensor advise please

[iib3327]

right my s2 doesnt wanna start and my vag com is saying

00513 Engine speed sensor (G20)
03.00 - No signal

now im guessing its the crank postion sensor but everywhere is listing different ones? what should i be looking for and where about is it located on the engine? (im guessing pas side engine pointing at flywheel?

sorry for the maybe silly question but im a newbie to s2's as this is my first one..

any help would be a great help..

Matt

[S2central.net]

Check your codes carefully - there is a typo here - there is no such thing as G20 (twenty).

The engine speed sensor is actually G28 (twenty eight). It is indeed at the flywheel on the UK passenger side.

If you search out a thread on 'Motronic sensors' or 'Engine Simulator' you will find waveforms that I have posted up... Its the only way to really know if that sensor is faulty or not.

The other thing to know is that when engine is not running - you get that engine speed sensor fault code on VAGCOM - and that doesn't mean its the reason doesn't start. This subject comes up a lot - I really need to document this all properly.

Here's a quick run down of the sensors needed to start the engine...

G4 - crank reference sensor - sits alongside G28 and provides one pulse every crank rotation - at 62 degrees BTDC on #1
G28 - engine speed sensor - driven by flywheel teeth - 135 teeth per crank rotation
G40 - camshaft position sensor - this hall effect sensor provides an 'active low' window every camshaft rotation

The fuel pump is activated by signal detection on G28.

There is NO spark until the ECU syncs onto the G4 and G40 pulses.

The most common reason for a 'no start' is a faulty G40 hall effect sensor. Easy way to check those with a 5V LED tester to see it blink every camshaft rev.
They can play up when cold or hot - often a trickle of water over them is the magic cure.

There are basic resistance tests you can carry out on G4 and G28 but they don't tell you an awful lot. Out of interest those two parts are identical but they carry different coloured plugs so you don't mix them up on the connector bay at the bulkhead.

Other dopey thing to check is fuses - don't take that the wrong way - wouldn't be the 1st time overlooked. Check the technical section at http://S2central.net for more details on ECU things - I am long overdue a big update on that info though

Paul

[UrS4boy]

It is common to get a false engine speed sensor fault code when you pull the codes when the engine isn't running.

Here is some G4 and G28 info that *might* help:

http://forums.audiworld.com/s4s6/msgs/116988.phtml

[AUDIS2avant]

Can we make this a sticky please??
This info is what i could use when my faults started, so would prob be a big help for newbe`s

[S2central.net]

Consider it stuck...

I've added the G4, G28 and G40 waveforms at idle as well.

Note that every alternate CPS pulse arrives within the window of the CMP pulse if the timing is setup correctly on the engine. When this signals arrive together, the ECU knows its at 62 BTDC on the compression stroke of #1.

[iib3327]

right then a new day a new problem, turned out to be a shafted fuel pump. new fuel pump on it ran perfect. taken it for an mot and it passed so well chuffed..

then... came to start it after we clayed it and nothing!
fuel pump is working so have fuel but not running... did have the G28 engine speed sensor fault come up as intermitant and cleared it but comes back up as no signal now..

so no im at my whits end with this car. first s2 and i hate the sight of it already!!!

any help would be a massive help..

Matt

[shark_90]

Don't hate, embrace! Welcome to the world of a £3k supercar You'll learn to love it and the satisfaction when fixing these daft little faults is immense

[Fat Audi 80]

Is it turning over and not starting (no spark or fuel) or is it dead, dead.

Give us some more info and we can help.

We have pretty much seen it all on here now, so someone will have the answer!

Cheers,

Steve.

[iib3327]

Is it turning over and not starting (no spark or fuel) or is it dead, dead.

Give us some more info and we can help.

We have pretty much seen it all on here now, so someone will have the answer!

Cheers,

Steve.

turns over, has fuel and seems to try to fire but then continues to turn over with no spark, plugs out reveals no spark? (i know thats a contradiction)

nothing on vag com other than G28 no signal

[S2central.net]

sigh.........

Looks like I'm really going to have to write the 'Dummies guide to fixing an S2 that won't start' - then post it up here as an UBER sticky.

[UrS4boy]

turns over, has fuel and seems to try to fire but then continues to turn over with no spark, plugs out reveals no spark? (i know thats a contradiction) nothing on vag com other than G28 no signal

Obviously, in order for the engine to fire you need fuel and spark and the correct timing of the delivery of each.

Never assume that just because you think a fuel pump is working that it really is. Break a fuel line connection and direct the flow into a container to confirm that the fuel pump is really working. You can use the ideas in this UrS4 post to jumper the fuel pump to test it for flow:

http://forums.audiworld.com/s4s6/msgs/89799.phtml

The fuel pump might work when jumpered but the FP relay might be dead or the cam position (Hall) sender might be dead (it should give a code but it might not).

If the cam sensor dies, the FP relay won't be triggered (at least on AAN) which means a bunch of stuff, including the fuel pump, the injectors, etc will also not be energized, as pointed out here:

http://forums.audiworld.com/s4s6/msgs/133907.phtml

G28 engine speed sensors can fail but it isn't common. Here is some G4 and G28 info:

http://forums.audiworld.com/s4s6/msgs/116988.phtml

Ignition switches can fail. This can lead to all sorts of problems.

This missing and hesitation diagnostic might help you sort things out as well:

http://forums.audiworld.com/s4s6/msgs/115408.phtml

Shorted coil pack wires (cracked insulation grounding on the coil pack or cam cover) can blow the coil fuse. This will let you crank until the cows come home with out ever producing any spark. I don't know where that fuse is on a S2 but on an UrS4 it looks like the one in the yellow holder on the right side of the photo in this post:

http://forums.audiworld.com/s4s6/msgs/254648.phtml

HTH. Good luck.

[iib3327]

i have fuel as i tested the pump to check and lots of fuel pressure coming from the pump. so if the pump fires i can asume the cam postion sensor isnt to blame? that was my next port of call..

as for starting an s2 for dumies thats not a bad idea as im a vw specialist by day and still cant get this thing to run so doubt your average joe blogs on his driveway would have much more resources..

so where now as im still in the same place i was nearly a week ago..?

[GT500]

"motor" fuses in the box.. check them.
Any immobilsers/alarm fitted?

[iib3327]

"motor" fuses in the box.. check them.
Any immobilsers/alarm fitted?

checked and double checked

checked every plug i can get to on the engine, checked all wires in the rocker/coils and no luck.. still just cranking..

[Fat Audi 80]

i have fuel as i tested the pump to check and lots of fuel pressure coming from the pump. so if the pump fires i can asume the cam postion sensor isnt to blame? that was my next port of call..

as for starting an s2 for dumies thats not a bad idea as im a vw specialist by day and still cant get this thing to run so doubt your average joe blogs on his driveway would have much more resources..

so where now as im still in the same place i was nearly a week ago..?

I am not sure the Cam Position Sensor stops the fuel pump on 3B / ABY. I thought it just controlled the timing of the ignition.

I would check your Cam Position Sensor is working, and have you tried the water down the back of the cambelt trick? This sensor is often one to let go and not allow firing of the ignition system. It is very hard to get to and test mind you. It can be tempermental too...

P.S. I am assuming you have an ABY, I don't think you have indicated anywhere?

HTH

Cheers,

Steve.