Slk 320 2002 Non starter

[paulwith]

Hi
My 2002 SLK will not turn over.
Battery is checked and fine, all lights and dash lights fine,but no contact.
Strangely the cooling fan cuts in after a few second although the engine is cold.
Green flag guy suggests an earth fault or inhibitor switch on the gearbox.
Also read suggestions of a relay.
Any thoughts please before I recover to garage.
Thanks.
PS I can't hear the fuel pump with ignition on, clue?

 

[Flyinspanner]

Wiggle your gear selector whilst trying?

 

[star]

Sounds like the aux fuse board with the k40 relays, under screwed down cover ns under bonnet.

 

[paulwith]

Sounds like the aux fuse board with the k40 relays, under screwed down cover ns under bonnet.

Wiggle your gear selector whilst trying?

Suspected k40 relay, anyway to DIY test?
Tried wriggling gear selector, no joy
Thanks both

 

[star]

I’d just replace or open up board and check for dry joint.

 

[paulwith]

Thanks Star
Now I'm confused, I thought I would try again this morning.
Ignition on , fuel pump running, started first time!
On an off a dozen times, running perfectly.
Now what? Read the codes while I can get it to my indy? Does this confirm your suspect relay?
Any thoughts?
Thanks

 

[star]

I don't think this fault will not show on any diagnostics, experience is the key.

 

[paulwith]

What kept you!?
I have a good local indy, should I ask him to replace the relay?
If the fault was the gearbox inhibitor would the fuel pump run?

 

[paulwith]

Update,went to start it today no joy, what's going on? Temperature?

 

[Ben Smith]

Could be a bad contact on the relay or even a bad contact on the ignition switch.

 

[Ben Smith]

If you want to test the relay theory, swap one for another. Obviously swap it with one that’s not critical to starting the car.
That will prove if it’s that relay causing an issue.

 

[paulwith]

Thanks Ben
Good idea-but, I have just tied it again,fuel pump running and first time start!
So where do we go from here?
PS I suppose the key is just a key and doesn't contain a "chip"
I have another key

 

[star]

What kept you!??

????

 

[paulwith]

My attempt at a joke because you replied instantly.
Any further suggestions, it failed this morning,then started,then failed, now started perfectly

 

[Ben Smith]

The key has a it’s own code and high is read by the transponder unit which will be around the steering column area. Once the key is read and the engine is started it won’t need to be accepted again.

I’ve had a similar intermittent problem in the past and it was the ignition switch, it was letting me start the vehicle every now and again then it would cut out after 2 minutes of running or the other scenario was it would drive absolutely fine and wouldn’t cause a problem.

It was a worn contact inside the switch.
So I changed the whole thing and it never caused an issue again.

It’s difficult to say which contact is letting you down, do you have an electrical drawing for this car if so I’ll take a look over it and see what else could be letting you down.

 

[paulwith]

Thanks Ben, if it's the ignition switch,what would explain the cooling fan running very fast with ignition on and no start?

 

[star]

My attempt at a joke because you replied instantly.
Any further suggestions, it failed this morning,then started,then failed, now started perfectly

Ok. The clue is in the fact that the fan starts up when the car doesn’t. It mean could the engine ecu isn’t powered up and the fan controller can’t see it and so powers the fan up to default setting. Now this a diagnosis on the net without seeing the car but I have seen this before.

 

[star]

I’m not convinced they are related, you would get the fan running constantly if the pressure transducer for the A/C gas pressure is open circuit or giving a strange analogue value back (faulty).

As I said, this is diagnosis over the net but it’s a known problem to check. But a good scattering of guesses will come good eventually. Here’s my educated guess.
https://www.slkworld.com/threads/my-slk-does-not-start-but-a-fan-does.27785/

 

[paulwith]

Thanks again,re. the AC It's been inop. for some time, seems there is a leak,didn't bother to fix it yet. Clue?

 

[paulwith]

Update, diagnosed by indy as K40.
Replaced with new. Runs fine.
Thanks for help.