Hello all. My 1994 s500 will not crank over. The dash lights all light up, battery tests good with load tester, no voltage drain when key is in crank position. It's just like a bad nss (I have tried starting it in neutral). I also tried locking and unlocking the door with the key. There is no click at all when key is turned. My question is, how do I diagnose the alarm vs nss, and can the nss be bypassed for diagnistic purposes. The car has had the underhood harness replaced about 2k ago and has only 66k original miles. Any ideas on how to do this or anything eldse that could be causing this condition would be appreciated.

My first check would be the fuse box..there is a feed fuse for the ATA relay that will effect starter lock out..I think it is #5, but not sure....

At least 3 possibilities...

SUBJECT:
GROUP 54 - MODEL 140, VEHICLE WILL NOT CRANK
FUSE FOR CIGAR LIGHTER BLOWN

The fuse for the cigar lighter (F3f16) in Model 140 vehicles also controls the starter lock-out relay module (K38) as of January 1994 production. If this fuse blows, the vehicle will not start. The practice of powering aftermarket electrical accessories from the cigar lighter plug increases the likelihood of this fuse being blown. Therefore, in vehicles that cannot be started due to a blown cigar lighter fuse, relocate the power supply for the starter lock-out relay module (K38) as described in the following work procedure:

To eliminate the possibility of a blown cigar lighter fuse (F3f16, Circuit 15R) preventing the vehicle from being cranked (by removing the power source for the starter lock-out relay module (K38), the supply wire for K38 should be moved from fusebox F3 position 21 (F3f16) to position 27 (F3f19) as follows:

1. Disconnect battery negative (-) cable.

2. Lift fuse block F3 to reach the wiring beneath.

3. Locate wire position 21 using the diagram on page 00-B.4/2 (drawing B). It is a RD/VI wire, covered with black tubing, near screw connection "D".

4. Remove the wiring connector from position 21 by sliding the red plastic locking clip over (press near letter "L" on fuse block) and pulling the wiring connector out. Slide the locking clip back into the locked position.

5. Locate wire position 27. It is near screw connection "E".

6. Install the wire from position 21 into position 27 by sliding the locking clip over (press near letter "M"), pressing the wiring connector into position, and sliding the locking clip back into the locked position.

8. Reinstall fusebox F3 carefully, avoiding damage to wiring.

9. Mark the fuse card with a permanent marker as follows: At fuse position 19, add the words "STARTER LOCK-OUT". If necessary (inspect fuse card), draw a hollow circle (to indicate a 7.5A fuse) and install a 7.5A (brown) fuse.

10. Reconnect battery.*

11. Test function of Starter Lock-out Relay Module by starting engine.

*NOTE: Be sure to re-code the radio and synchronize the power windows after reconnecting the battery.

Attached Thumbnails

   

__________________
1995 S600, 1 of 618 (sold)

"Speed is just a question of money...how fast you wanna go?"

LONG LIVE THE W140!
Visit my Web Page at www.v12uberalles.com

Very good info.
That is lock-out fuse I refer to. Glad to see they made an design change.

Thanks for the info, but the fuse is good.

Look and see if there is a 3 wire plug connector on the engine firewall , just to the left [ looking from front of car] of brake reservoir. This should be on a firewall between brake booster area and engine.

I havent completely removed all the cowling but from what I can see there isnt one.

OK
It would not require removal of anything to see if it were present.
The E class has one and that is the plug that feeds the starter solinoid, so we just use it as a test point..but I did not know if the S class was using the same...
Guess they do not use the same starter set-up.... ..

How about the location of the lockout relay? I subscribed to Alldata but they only show back to 96 and show it in the fuse panel but mines not there. Thanks

I don't have S class schematics, but on E class of same year, the k38 is behind the speedo cluster.
And the NSS can be jumpered under the dash, by the brake pedal.

The starter series circuit goes like this

Bat power to Ignition sw> to NSS ,> to K38 relay contact, >to plug I mentioned under hood, to starter solinoid.
I use the plug under hood and bring 12v from battery to the center terminal.. if that engages starter [ as it should ] , I then know the problem is upstream from that test point. meaning NSS/K38/K38 fuse/igfn sw.
if no starter activation at the test point , it is down-stream [ meaning starter motor/sol/wires ]
look around for a 3 wire plug near the brake res. The cenetr wire is V/Yl on the E class.
..or maybe someone here has an S classs/140 schematic..that is the best bet .

Schematic.

Attached Thumbnails

     

__________________
1995 S600, 1 of 618 (sold)

"Speed is just a question of money...how fast you wanna go?"

LONG LIVE THE W140!
Visit my Web Page at www.v12uberalles.com

I have no solution, just a story what happened to me last week.

The infrared key did not unlock but changed the red blinking sign in the mirror to green. So I unlocked manually and drove the car. Later this day, the remote locking was back to normal.

Next day when I was turning the key, the starter didnīt crank. The mirror lamps were going red-green-red-green. Did check for fuses and tried neutral and was afraid the starter was gone. Left the car for two days and then all was working as normal again!

After one week of back to normal, I donīt really know what happened, but it seems to be too much electronics in our cars.... (This was my G500)

__________________
-94 E 36 AMG Coupé, Brilliant Silver
-98 G 500, Obsidian Black
-05 Mini Cooper, Solid Black
-97 993 Carrera S, Ocean Blue

Very Good...
Schem. shows fuse #2 as K38 relay feed .
The jumper pins for K38 test would be 1/3 for by-pass .
Now just need Starter schematic for the rest [ from NSS]

I am not sure if the schematic I have is correct for USA cars but the following might be of assistance;

Violet wire from pin 50 on ignition starter switch to pin 3 on starter lockout relay.
Violet/White wire from pin 1 on starter lock out relay to pin 8 on neutral switch.
Violet/White wire from pin 3 on neutral switch to starter solenoid.
Red/grey wire from fuse #16 (rear fuse box) to pin 4 at starter lockout relay.
Brown/grey wire from pin 5 of starter lockout relay to pin 25 of the infra red control module in the luggage compartment.

<>

What schematic do you have????
The one listed shows k38 feed to pin 4 as fuse #2 in rear F-4 fuse box.