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I have a 2005 SL 500 and my problem is it will not start…

Customer Question
I have a 2005...

I have a 2005 SL 500 and my problem is it will not start meaning that the starter will not turn over. Both batteries are fully charged and Britney now over 12.5 A car started fine parked at the hospital for about an hour The car will not turn over.

Mechanic's Assistant: Have you checked the battery, particularly the terminal connections? Are they corroded?

Both Batteries are fairly new clean and fully charged

Mechanic's Assistant: Are you fixing your SL yourself? What have you tried so far?

Check fuses and relays check the key Farb FOB it opens the doors and will turn the key slot but it does not start

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Dash lights will not turn on past the first Click of the key

Submitted: 8 months ago.Category: Mercedes
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Answered in 42 minutes by:
11/16/2017
Mercedes Mechanic: Matt, Engineer replied 8 months ago
Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 23,314
Experience: Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Hello

If the car's not cranking then first check it can turned over by hand by using a socket on the crank pulley nut, so double checking for any mechanical issues

If OK then check that the main battery cables are on tight and the terminals are clean and bright. Do the same for the engine / gearbox earth strap.

Then follow the main positive lead back to the engine and down to the starter motor, and check the connection at this end as well.

There should also be a small wire to the motor which should have 12V when you're turning the ignition switch / pushing the start button to crank. If the 12V isn't there, check back along this wire for damage to the insulation or corroded connections

This 12V feed comes directly from the ignition switch / starter button so this may be faulty and need replacing

Check the resistance of the main positive lead that runs down to the motor as anything more than a few ohms and it should be replaced

Don't forget to try a jump start from another car / battery as its possible the battery is poor, if you have a voltmeter a healthy battery should read 12.7+V

also try substituting the battery for another as I've known a very flat battery to drag down the system voltage too far even with jump cables

one other thing to consider is that the immobiliser is faulty and preventing the starter from being enabled - however if the dash / ignition lights are on then this usually means that its off

If this is all OK then its possible the car needs a new starter motor

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Mercedes Mechanic: Matt, Engineer replied 8 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

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Customer reply replied 8 months ago
When i To check it out and then I will reach you
Customer reply replied 8 months ago
What about the brake Switch if it’s not functioning the neither was the starter Norwood it let the gearshift to come out of park when I first get in the dash lights come on but if I turn the key then nothing
Mercedes Mechanic: Matt, Engineer replied 8 months ago

Hello

I'd agree that its well worth investigating the connections to the brake pedal switch and the wiring to it for any crimp damage or fraying. Ideally use a multimeter to check that the switch is working OK. This is because the gearbox controller won't allow the lever to shift from park until it sees that your foot is on the brakes

There should be 2 switches one for the brake lights and the other for the gearbox and both are located at the top of the brake pedal in the drivers footwell.

If this is OK then check the selector lever linkage for any broken parts and or missing bolts or if a bolt is partially out and is jamming things up

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Mercedes Mechanic: Matt, Engineer replied 7 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Customer reply replied 7 months ago
Matt check all items that you have presented and it was down to possibly the keyswitch when you put the key in dash lights come on but when you turn it there are no additional wise like there should be the Windshill wipers brake lights don’t work so I’m thinking it’s something to do with the key if you replace the keyswitch do you need to reprogram it and in this only beBy the dealer
Mercedes Mechanic: Matt, Engineer replied 7 months ago

hello

Ok usually if the key has an issue with the security then you'll get a flashing 'car' or ' key' symbol on the dash

however its also possible the key switch is faulty

and while you can replaced the switch yourself they do need to be programmed up by a dealership so it matches the VIN of the car and communicates to the ECU correctly

this blog post shows how the switch is replaced - sorry its not a more DIY answer but thats often the nature of security systems

http://www.pelicanparts.com/techarticles/Mercedes-W203/BODY-Replacing_Your_Electronic_Ignition_Switch/BODY-Replacing_Your_Electronic_Ignition_Switch.htm

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Mercedes Mechanic: Matt, Engineer replied 7 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Customer reply replied 7 months ago
Matt found that the SAM unit on the right side may have gotten wet it is corroded this is the unit that Houses both the fuse and relay for the starter. Ordered a new one should be here in a couple days I’ll keep you informed as to what I find
Mercedes Mechanic: Matt, Engineer replied 7 months ago

understood

good luck

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Mercedes Mechanic: Matt, Engineer replied 7 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Customer reply replied 6 months ago
Matt i have replaced the EIS still not getting power to the starter relay when the key is turned to the start there are no dash lights, and no start the back
Customer reply replied 6 months ago
battery is new but will drain over nite the windows will not work is the rear sam not working
Mercedes Mechanic: Matt, Engineer replied 6 months ago

Ok

Next I'd check the current drain aspect, the best way to find what circuit is causing the excessive currant drain is to fit a current sensing multimeter in series with the positive battery lead on the car and the battery, or use a current clamp meter on the battery positive cable.

A typical current drain with everything off and un-alarmed should be around 0.05Amp and if its higher than this remove a fuse and re-measure, if measurement doesn't change then replace the fuse and remove the next.

Once you've isolated the circuit with the excessive drain check the wiring connections and plugs to components and the wiring harness that runs by the engine bay fuse box - the wiring harness chaffs / rubs through and gets damaged - but its not always easy to see so be careful when checking..

Also check that the alternator is actually charging the battery in the car by taking a battery voltage reading with the engine off then another with the engine running. The 2nd reading should be higher than the 1st and climbing steadily. And also check that the alternator is secure to the engine as this provides the ground for the charging circuit and make sure that the engine / gearbox earth strap is secure and the contacts are clean and bright.

if the alternator appears not to be working - take it to a electrical specialist and ask them to test it as sometimes you can replace just the diode pack and this will repair the alternator without requiring replacement

And one last thing is – how old is the battery? – As even good quality ones need replacing every 5 years and faulty battery just won’t hold a charge

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