[SkylerW]

The posts I found on testing the starter all seem to deal with the later w210s using the K40 relay but perhaps I am missing something. I am thinking my model doesn't have the K40 or I haven't found it. I have a strange situation or at least the progression seems strange to me. On Friday afternoon, I went to start my car and there was like a jolt (cranking) but it didn't start. Then when I tried to start, two or three times I only got a buzzing noise behind the dash but no cranking at all. Then the next try it fired right up. When I got to where I was going and had to restart the car again, I had maybe four or five attempts with the buzzing sound but no crank and then the next it started right up and I got home. The next morning the car fired right up on the first attempt. Then coming home it required another three or four tries with no crank and then fired up on the next attempt. I made it home but then later in the day and since when I turn the key I only hear that mild buzzing sound (which seems to come from the area behind the driver side fuse box where there are some cables plugged in) but the car does not crank at all.

I replaced the battery today because it was due for that anyway and it made no difference. Since the car drove just fine the times it did start, I'm assuming it is not the fuel pump. I want to check the starter or maybe the starter relay but I'm not sure where it is located or how to check. I'm hoping it's the relay and not the starter itself after reading that it is a pain to replace the starter. I already checked all the fuses under the hood that I could find and the ones under the back seat just in case.

 

[ffgtium]

Edit: Wrong car.

The basic little relays are with the fuses under the hood. However, you will have to remove the whole lid to the housing, as the relays are not accessible from the hinged panel. Getting the last screw in the back should be easier if you set your hood to the fully vertical position.

There is another fusebox under the rear seat by the battery, but I don’t remember what is in it. I did replace my K40 a few years back, and if memory serves it was in the black case above the radiator expansion tank with all the other computer stuff. I found a pdf in my files that gives an approximate location of the relays.

You can pull the starter off the car and jump it with a car battery if you really want, but I’m sure someone else has an easier/better solution. Its in an awkward spot so you will need a few extensions and a u-joint (probably the wrong name) for your socket wrench. Not super easy but I’ve done it a few times. Be sure not to drop it on yourself once you have it free, as it is heavy. Also getting it around the steering column can be difficult.

Do you have any other weird electrical gremlins? A lot of seemingly unrelated systems run through the same components on these cars

 

[mrboca]

The posts I found on testing the starter all seem to deal with the later w210s using the K40 relay but perhaps I am missing something. I am thinking my model doesn't have the K40 or I haven't found it. I have a strange situation or at least the progression seems strange to me. On Friday afternoon, I went to start my car and there was like a jolt (cranking) but it didn't start. Then when I tried to start, two or three times I only got a buzzing noise behind the dash but no cranking at all. Then the next try it fired right up. When I got to where I was going and had to restart the car again, I had maybe four or five attempts with the buzzing sound but no crank and then the next it started right up and I got home. The next morning the car fired right up on the first attempt. Then coming home it required another three or four tries with no crank and then fired up on the next attempt. I made it home but then later in the day and since when I turn the key I only hear that mild buzzing sound (which seems to come from the area behind the driver side fuse box where there are some cables plugged in) but the car does not crank at all.

I replaced the battery today because it was due for that anyway and it made no difference. Since the car drove just fine the times it did start, I'm assuming it is not the fuel pump. I want to check the starter or maybe the starter relay but I'm not sure where it is located or how to check. I'm hoping it's the relay and not the starter itself after reading that it is a pain to replace the starter. I already checked all the fuses under the hood that I could find and the ones under the back seat just in case.

Are you talking about the 1995 E300D?

Your title says 1997 E420, but there is no car like that in your profile.

In any case, for both cars the starter circuit is similar. In the case of 1997 E420, the P/N switch is in the transmission (722.6) and monitored by the engine computer, so the violet wire from the X22 directly goes to the starter solenoid. For 1997 E420, make sure that the shifter is in P or N (you can try to start in N too). So it is another area you need to look at.

The starter circuit starts from the ignition switch (violet wire) which goes through the relay contacts (N65 module relay K2), then to the terminal block X22/1 as shown

You need to remove the cover to expose the terminals. You will see the violet wire is terminated there. That is the start wire that is connected to the transmission start inhibit switch mounted on the transmission itself. From the start inhibit switch (which provides a closed contact only in gears P/N), the start wire goes to the starter solenoid.

You could start at the X22/1 terminal block. You should see 12V on the violet wire when someone tries to crank. If you do, the problem is downstream (P/N switch, wiring, grounding, starter itself). You can apply 12V on the violet wire terminal to crank.

If you do not see 12V at the violet wire terminal while cranking, then the problem is either the ignition switch, or the K2 relay at the driver's side close to the firewall (n65 module), or wiring.

 

[SkylerW]

I really needed to update my car list. That was what I had a few years back but for now am down to the 97 E420.

Thank you for those replies. I need to get a hold of a 12V probe as I'd like to check if the starter will engage with that. Later today, I'll try to get a friend to come so I can check the voltage at that wire when cranking.

I remember with my W124s that I could do a wire bridge at the relays to check things like the fuel pump and starter to see if they would engage and was hoping this offered the same option but I will look at getting the tools I need for these checks. I realized last night that mine does have the K40 under the box on the passenger side. I have heard that that can require resoldering for starting issues but my issue seems more sudden in starting rather than a relay circuitboard slowly deteriorating.

 

[mrboca]

I really needed to update my car list. That was what I had a few years back but for now am down to the 97 E420.

Thank you for those replies. I need to get a hold of a 12V probe as I'd like to check if the starter will engage with that. Later today, I'll try to get a friend to come so I can check the voltage at that wire when cranking.

I remember with my W124s that I could do a wire bridge at the relays to check things like the fuel pump and starter to see if they would engage and was hoping this offered the same option but I will look at getting the tools I need for these checks. I realized last night that mine does have the K40 under the box on the passenger side. I have heard that that can require resoldering for starting issues but my issue seems more sudden in starting rather than a relay circuitboard slowly deteriorating.

Yes, there is a K40 fuse and relay module for your modeland model year, but this is not involved in cranking the engine. If you had an issue with crank but no start, then K40 would come into the picture.

As I said, here is a relay called K2 which is responsible for cranking the engine when the key is turned to position 3. The purpose is to prevent contact erosion in the ignition switch as the relay contact closure is much faster and carry heavier current for the starter solenoid.

If you hear buzzing from the driver's side under the hood with key in position 2, then the relay is not the problem as it is not powered at this stage. If you hear buzzing while cranking, the chances are that the relay is bad.

 

[SkylerW]

MrBoca, thanks for the clarifications. My configuration is a little different compared to the first pictures you sent. There is nothing in the place of the x22/1 terminal block. I attached a picture. I did find a violet wire in the K2 relay behind my fuse box. That seems to be the area where the buzz noise comes from when I turn the key to position three. If the car is in P or N, that buzz is there when I turn to position 3 but if in any other position it won't which I'm hoping means at least the shifter position isn't an issue. I need to look more closely but it looks like that K2 box is a whole piece. I don't see separate relays on it, just connectors at the top. I included a picture of my K40 as well just for reference.

 

[SkylerW]

Is that purple wire where I would need to apply 12V since I don't see the x22/1 terminal block? I'm assuming this doesn't have a spot like my w124s where you can use a bridge wire to check things like the starter or fuel pump just to see if functioning. Thanks for all the help so far.

 

[Witek_M]

Take broader picture of right module box. You are looking for connector X22 pin 1. Violet/white coming in violet to the starter solenoid.

 

[mrboca]

Is that purple wire where I would need to apply 12V since I don't see the x22/1 terminal block? I'm assuming this doesn't have a spot like my w124s where you can use a bridge wire to check things like the starter or fuel pump just to see if functioning. Thanks for all the help so far.

You can apply 12V to the purple / white wire which goes to the starter via X22 terminal block to check the starter. No need to turn the key to position 3, or even insert the key. The module you are pointing to is N65 module . K2 relay is part of this module.

 

[SkylerW]

Okay, I found a green plug with lots of wires connected to both sides in that module area on the passenger side. That violet / white wire is connected there. Just to confirm, I would apply 12 volts at that point or is it just the same to apply it on the driver side where it's connected to the n65 module? Am I correct in thinking that the whole n65 module would need to be replaced if the K2 relay is bad? It looks like all one piece. I still can't tell if there's a special trick to remove it. It looks like it just slides down in but if I try to pull up it won't move and I don't want to break anything

 

[mrboca]

I would first measure the voltage on the violet / white wire (backprobing, piercing with a pin) to see if it has 12V with key in in position 3. It should as it goes to the starter solenoid. If it does not, you either have a bad ignition switch, or a bad k2 relay contact, or loose wiring / connecter somewhere between them.

Once you confirm that the N65 / K2 is bad, then you can remove the N65 module.

 

[SkylerW]

I'll have my son home in a little while to turn key while I check the voltage. If that k2 relay is bad, does the whole module have to be replaced? As I mentioned, is there a trick to module removal? Didn't want to break trying to slide out

 

[mrboca]

Never have to remove one. Once you get the connectors out it should slide out. The only thing that looks like a latch seems to be at the bottom.

Maybe there are latches at the sides where the "rails" are.

Note that this module controls more than the crank. It has logic for the ABS pump, aux fan control, etc. So what is buzzing may not be the K2.

 

[SkylerW]

I did some voltage checking. I attached a picture where I removed the violet / white wire from the n65. With my son turning The key to position 3, there is 12 volts at the pin on the n65 where that wire would normally connect to. I don't know if that means anything. I couldn't get a reading at the green connector on the passenger side where it goes into plug 1. It's very tight in the hole and I couldn't get my probe in next to the wire.

 

[SkylerW]

It's interesting that if that wire is connected to the n65 it makes a buzz sound when I turn to position 3 but if that wire is disconnected there is no buzz sound

 

[Witek_M]

I did some voltage checking. I attached a picture where I removed the violet / white wire from the n65. With my son turning The key to position 3, there is 12 volts at the pin on the n65 where that wire would normally connect to. I don't know if that means anything. I couldn't get a reading at the green connector on the passenger side where it goes into plug 1. It's very tight in the hole and I couldn't get my probe in next to the wire.

Get back probe kit. It works in very tight places.

Tool Aid - 20 Piece Back Probe Kit (23500) , Blue - Automotive Car Care Tools And Equipment - Amazon.com

Tool Aid - 20 Piece Back Probe Kit (23500) , Blue - Automotive Car Care Tools And Equipment - Amazon.com

www.amazon.com

 

[SkylerW]

Now I know there is 12 volts coming to that connector where the violet / white wire connects. That wire then leads to the starter solenoid right?

 

[SkylerW]

That looks to be the same wire coming in to the green connector shown in the attached image into PIN number one on the left side. I'm not sure where it goes from there. The wire on the other side looks almost brown coming out of pin 1 but maybe that's the violet

 

[mrboca]

You need to use a needle to poke into the violet/white wire insulator at the green connector to read the voltage (poor man's probe). Then touch the probe tip while someone tries to crank. Do this with the N65 end connected to the module, so you can see if there is any voltage drop while cranking. You can check the voltage on the violetish wire too under the same conditions by piercing into this wire while in pos 3.

 

[SkylerW]

Just to confirm also, to check the starter itself by applying 12 volts, I would put 12 volts to the wire coming out of the right side of the green connector, correct? I'm really discovering some of my ignorance about testing electrical components in this process. It has always felt the most confusing for me.