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2003 ML350, 2005 E500, 2007 E63
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3 Posts
Discussion Starter · #1 ·
Hello,

Just want to start off with saying I'm fairly inclined when it comes to diagnosing and fixing Mercedes.

2003 ML350 is experiencing some sort of curse.

I just recently parked it after selling the catalytic converters. Has always started up and never given me trouble.

Now returning to the car a week later I charged the battery and moved the car again like normal.

A few days go by after doing some maintenance. (Did full conductor plate service, new belt, tensioner, water pump, and idler pulley.)

Put in a fully charged battery, went to start, nothing, no crank, no fuel pump sound.

After a lot of reading about these issues over the forums I still haven't found a fix that works for mine.

All the maintenance I did doesn't interfere with any of the components meant for starting.
-All the lights on dash light up.
-Red security led blinks once when keys inserted & turned.
-Checked all fuses and switched relays with known working relays, nothing.
-Checked ground cable @ starter/solenoid, cleaned the wiring (had some blue corrosion but isopropyl alcohol cleaning made it clean.)
-Starter gets power and will crank when I jump the starter relay, but car won't turn over to start.
-Can hear fuel pump turn on when jumping the fuel pump relay.
-Opened ECU, no rust, no oil, no contamination, saw some hardened amber looking stuff on the motherboard I cleaned off with isopropyl alcohol. I've seen this plenty of times on many TCUs that worked fine? Still didn't fix.
-Double checked all sensors, fuses, relays are connected correctly.

I'm stumped. No codes but only for undervoltages @ steering angle sensor most likely due to the battery dying.

Have fixed over 10 Mercedes with no issues as long as the fuses, battery, spark, fuel were good. I've even gotten some junk yard Mercedes to start right up.

I'm fairly certain its an ECU connection problem thats preventing the starter and fuel pump to turn on.

馃う馃う馃う馃う馃う馃う
 

Outstanding Contributor
2002 ML320, 2003 A160, 2002 ML500, 2018 GLS350d
Joined
4,450 Posts
Fuel pump only switches on for 1 sec upon key to position 2. Then on again when cranking and running.

I think it might be time to replace your ignition switch. There are tests you can do first, if you want.
 

W163 and General M Gremlin
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6,887 Posts
Welcome to BW Hydrotsunami,
Good to have you as a new member.

Please complete your BW registration. ===> user CP profile
====>
click on your icon----> click on Account Settings---->
goto Account Details----> add vehicle details---->
ADD your make model YEAR ----> click save.
 

Registered
2003 ML350, 2005 E500, 2007 E63
Joined
3 Posts
Discussion Starter · #4 ·
Fuel pump only switches on for 1 sec upon key to position 2. Then on again when cranking and running.

I think it might be time to replace your ignition switch. There are tests you can do first, if you want.
Fuel pump only switches on for 1 sec upon key to position 2. Then on again when cranking and running.

I think it might be time to replace your ignition switch. There are tests you can do first, if you want.
UPDATE
found out that I can start the car by jumping starter relay and then turning key to pos 3 to start.

But can't start by itself.

Only thing I can recall messing up on is while installing the conductor plate I forgot to slide the orange/yellow slider onto the pin.

I don't think this should cause a no start condition? Only remembered this while brainstorming because I was able to start the car but it acted in limp mode.

No trans codes. So I know everything good and its only because I didn't connect the slider onto the pin.

As far as I know I can completely disconnect the TCU plug and the car will still start. So still confused on why it just won't crank.
 

Registered
Dallas, Texas
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9,297 Posts
As far as I know I can completely disconnect the TCU plug and the car will still start. So still confused on why it just won't crank.
Now, put your joint aside and put your sentence together with some brake points.
1. Key in
2. Key in position 1
3. Key in position 2
4. Key in position 3
 

Outstanding Contributor
2002 ML320, 2003 A160, 2002 ML500, 2018 GLS350d
Joined
4,450 Posts
So still confused on why it just won't crank.
When you bridge the connections of the starter relay, you are bypassing the function of the ignition switch when you turn the key from position 2 to 3.

At your mileage, plastic parts inside the ignition switch wear out after repeated use. Then it no longer closes circuit 50 every time you want it to. Eventually, it stops working completely.

The rest of the ignition switch works fine. So you can drive the car if you turn to position 2 and momentarily power the starter.

Some owners have jury-rigged a start button to avoid replacing their ignition switch, a tricky task that can take longer than 10 minutes.
 
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