Intermittent no crank?

[J. M. van Swaay]

94 E500, 125K miles.

Intermittent no crank. Very intermittent, probably happens once per 30 starts. Originally thought fuse 5 was faulty because starter engaged after replacing fuse 5. Then a few days later, no crank again. During troubleshooting, problem mysteriously fixed itself, now have about 20 good crank/start cycles. After a search of past posts, I’m aware of the normal culprits, ignition switch, battery, battery connections, NSS, starter wire harness decay, fuse B and C, alarm immobilizer/K38 relay, and the starter itself. Easy items to check have been checked, nothing noteworthy found.

I’m OK to just drive the car until the problem becomes more frequent thereby making diagnosis possible. The problem with this is that I don’t want to be stranded away from home if the problem happens again. On my E320’s it was possible to start the car from under the hood by placing the ignition switch in the run position and then jumpering +12v to the center pin of the three pin connector behind the the brake booster. IIRC, this would bypass the ignition switch, the NSS, and the K38 immobilize function. If you had a good battery, good battery connections and a good starter, it would start and run.

Does this work on the 94 E500? If not is anyone aware of another simple bypass solution to at least prevent a stranding?

Thanks,

J. M. van Swaay

 

[gsxr]

On my E320’s it was possible to start the car from under the hood by placing the ignition switch in the run position and then jumpering +12v to the center pin of the three pin connector behind the the brake booster. IIRC, this would bypass the ignition switch, the NSS, and the K38 immobilize function. If you had a good battery, good battery connections and a good starter, it would start and run.

Does this work on the 94 E500? If not is anyone aware of another simple bypass solution to at least prevent a stranding?

If the starter is good, then yes, the bypass procedure you described above will work. It's actually how the FSM says to perform a compression test, cranking the engine using the connector behind the CAN box. I'm not aware of any other foolproof bypass solution.

For the random no-crank issue... if the starter is old or original, there's a slight chance the solenoid is failing.

 

[gerryvz]

My first thought is also with the starter/solenoid for this.

 

[J. M. van Swaay]

Thanks for the replies!

I have not noticed a gradual decrease in the strength of the starter motor. When it does crank, it cranks strong—nothing to indicate a failing motor. I have not looked closely but I assume the solenoid is part of the starter. Can it be replaced separately or does this involve replacing the whole starter?

 

[gsxr]

The solenoid is integrated with the starter, not available separately.

One way to test if the solenoid is at fault: next time the starter won't engage with the key, trying applying +12v to the center pin at the harness. If it engages, the problem must be upstream. A related test is to see if you get +12v at that center pin when turning the key to "start" and the starter doesn't engage. No voltage (or, reduced voltage) would also indicate an upstream problem.

 

[J. M. van Swaay]

Have not crawled under the car to look at the starter but is it possible to ”jumper“ the solenoid? Many years ago (old chevys and fords) we would do this with a screw driver across the two terminals but that was when the solenoid was separate from the starter. Probably not that safe but we did get starts with failed solenoids...

 

[gsxr]

Have not crawled under the car to look at the starter but is it possible to ”jumper“ the solenoid? Many years ago (old chevys and fords) we would do this with a screw driver across the two terminals but that was when the solenoid was separate from the starter. Probably not that safe but we did get starts with failed solenoids...

Save your back, don't crawl under there. The starter and solenoid assembly is tucked behind a heat shield, and has plastic caps over the main terminal. And all that is sandwiched between the block, exhaust pipe, engine mount bracket, and steering linkages. You cannot access it from below without a lot of effort... which is why your idea to use the center pin of the 3-pole connector behind the CAN box is infinitely easier.

 

[J. M. van Swaay]

Thanks for your infinite wisdom.... If this were a manual transmission, all of this would be much easier... Wonder how many of todays drivers have at one time “push started” a manual transmission vehicle. I remember this procedure rather well. Prior planning was often helpful, if you could park on a slight incline with room to roll, you didn’t even have to push. Maybe I’m showing my age....

 

[J. M. van Swaay]

the FSM says to perform a compression test, cranking the engine using the connector behind the CAN box.

The procedure I’m aware of describes jumpering via the three pin connector on the drivers side of the firewall behind the brake booster. This works on the E320. I don’t think it works on the E500. I did some trouble shooting today... everything is currently working normally and I tried the procedure using the three pin connector behind the brake booster-it did not work but the car started normally just before and just after trying this procedure. Dave, you mention a connector behind the CAN box for this procedure. Am I correct that the CAN box is on the passenger side at the firewall? (Has a round black cover that you remove to access the round connection pin block to check for codes...) If so, there is a cable connection block under a black plastic triangular shaped cover behind the box. It appears that battery cable and starter cable connections are here. If the FSM crank procedure involves this connection block I’m not familiar with it. Any chance someone can point me in the right direction?

Thanks,

J. M. Van Swaay

 

[emerydc8]

Your start symptoms sound just like mine did. It went on for at least a year. When the starter cranked, it usually worked well. Occasionally, it would crank very slowly and not start (like the battery was weak), but if I waited a few seconds and tried it again it would usually work -- until one day it didn't and left me stranded at the post office.

It turned out to be the starter. Like Dave alluded, getting the heat shields off is more than half the work in replacing the starter, so it would pay to just replace it once you've gone that far. For the two large Allen bolts that hold the starter on, I found a 20" extension (1/2" drive) and a universal swivel make the job much easier.

 

[gsxr]

The procedure I’m aware of describes jumpering via the three pin connector on the drivers side of the firewall behind the brake booster. This works on the E320. I don’t think it works on the E500.

JM, the principle is the same, but the connector is in a different location. On the 6-cyl cars, the 3-pin connector is on the driver side on the firewall ahead of the master cylinder (NOT behind the brake booster, that connector is visually identical but is for the HVAC blower motor, not the starter).

On the E500E specifically, the 3-pin connector which will engage the starter is located behind the CAN module box on the passenger side.

I did some trouble shooting today... everything is currently working normally and I tried the procedure using the three pin connector behind the brake booster-it did not work but the car started normally just before and just after trying this procedure.

Eeek. I hope this didn't hurt anything on the HVAC side.

Dave, you mention a connector behind the CAN box for this procedure. Am I correct that the CAN box is on the passenger side at the firewall? (Has a round black cover that you remove to access the round connection pin block to check for codes...)

Yes, that is it!

If so, there is a cable connection block under a black plastic triangular shaped cover behind the box. It appears that battery cable and starter cable connections are here. If the FSM crank procedure involves this connection block I’m not familiar with it. Any chance someone can point me in the right direction?

You don't need to mess with the connections on the bottom behind the box. You want the 3-pin connector on the rear of the CAN box.

The FSM diagram (section B at this link) is NOT very clear.

 

[J. M. van Swaay]

Thanks Dave!!!! Your knowledge of these cars never ceases to amaze me. Members of the forum are very lucky that you are so willing to share your expertise! I had my connectors confused. The last time I used the starter lockout bypass procedure on one of my E320s was probably ten years ago. I remember it involving a set of jumper cables and a screw driver to make contact with the pin, I got the car started and got it home. Guess now I don’t remember which connector was involved... Thanks again for setting me straight. And by the way, there was no damage to the blower control module after my boneheaded mistake. HI low and auto blower functions all work as they should....

Thanks again!

J. M. Van Swaay

 

[Kyiv]

Thanks Dave!!!! Your knowledge of these cars never ceases to amaze me. Members of the forum are very lucky that you are so willing to share your expertise!

If Gerry is George Washington of this forum, then Dave is Abraham Lincoln.

 

[cascade]

If Gerry is George Washington of this forum, then Dave is Abraham Lincoln.

@gerryvz = Vladimir Ilyich Ulyanov (Lenin)
@gsxr = Ioseb Besarionis dzе Jughashvili (Stalin)
@xfadmin = Vyacheslav Mikhailovich Skryabin (Molotov)
@kiev = kulak / kurkul

 

[gsxr]

@The Emperor = ...?

(Palpatine?)

 

[Randy Crooks]

On the E500E specifically, the 3-pin connector which will engage the starter is located behind the CAN module box on the passenger side.

I've been having the same problem with my 1991 500E. It will sometimes have a slow cranking starter motor but it would always start, recently it has had a clicking noise that sounds like the solenoid when I turn the key to the start position and the starter motor doesn't engage but if I try it two or three times it will engage and start right up. Last week it finally quit completely, no clicking no matter how many times I tried to engage the starter, so it seemed like a new starter would probably fix the problem and it is likely the original so it was time anyway. I replaced the starter yesterday but still nothing when I try starting. I have a full battery, I have put 12 volts to the middle (Male) pin on the three pole connector behind the CAN box and the new starter works fine, I put a meter on the middle (Female) pin on the three pole connector and get 12.6 volts when I turn the key to the start position, but when I plug the connector back together there seems to be no power flow to the starter.

My fuel pumps run, all the dash lights come on, the reverse lights work properly, all the connections look nice and clean with no corrosion. I was going to try bypassing the neutral safety switch but if there's power (12.6 volts) all the way up to the female end of the three pole connector it makes me think the NSS is working.

I have a basic understanding of electrics but after three or four hours of thinking and overthinking I usually get a headache and need to walk away and take a break and I'm at that point now. So I have to ask for advice from anyone who maybe has had something like this happen on their car.

Thanks,
Randy

 

[gsxr]

Schematic below from the ETM... only items in the circuit appear to be the ignition switch, and NSS.

 

[gerryvz]

I concur - it's either the neutral safety switch, or less likely the ignition switch.

If your ignition switch is working, you should hear your fuel pumps run for a second or two to pressurize the system (sounds like this is the case). If you have not replaced the NSS, would be a good time to do this.

There is a HOW-TO on this here.

Note that the factory MB NSS is now NLA.




However, it can be purchased via aftermarket sources, such as AutohauZ ($$), FCP Yurro ($$$) or RM Yurropean ($).

I would actually beseech EVERYONE on this forum to purchase at least one NSS as a spare, as these may not be available forever. Certainly NLA from MB.

Cheers,
Gerry

 

[gsxr]

I'm not sure if the ignition switch has a dedicated output for the starter... if so, it could have a failure mode where everything else works normally, but doesn't pass enough current to engage the starter solenoid. (??)

 

[Randy Crooks]

I'm not sure if the ignition switch has a dedicated output for the starter... if so, it could have a failure mode where everything else works normally, but doesn't pass enough current to engage the starter solenoid. (??)

That's what I've been thinking. There is a signal at the middle female part of the three pole connector when I turn the key to the start position and it shows 12.6 volts but it won't make the solenoid even click, when I put 12 volts from the cars battery on the middle pin the starter works fine. I'll need to somehow check the amount of current on that middle pin with the ignition switch in the start position or just replace the NSS and go from there. The connector on the NSS looks clean but the identification numbers/letters are hard to see, would you know which two I need to connect together to try a bypass so I can double check that switch, I did see on this forum somewhere that it should be pin number 8 and 9 but my NSS connector is unreadable. In the schematic you sent is that H3/1 control unit a simple relay? I was wondering if that needs to be checked in case it is required to properly complete the circuit to the solenoid. Thanks for your help, it's really appreciated.

 

[Randy Crooks]

I concur - it's either the neutral safety switch, or less likely the ignition switch.

If your ignition switch is working, you should hear your fuel pumps run for a second or two to pressurize the system (sounds like this is the case). If you have not replaced the NSS, would be a good time to do this.

There is a HOW-TO on this here.

Note that the factory MB NSS is now NLA.
View attachment 169383



However, it can be purchased via aftermarket sources, such as AutohauZ ($$), FCP Yurro ($$$) or RM Yurropean ($).

I would actually beseech EVERYONE on this forum to purchase at least one NSS as a spare, as these may not be available forever. Certainly NLA from MB.

Cheers,
Gerry

I'm ordering one right now, thanks.

 

[gsxr]

In the schematic you sent is that H3/1 control unit a simple relay? I was wondering if that needs to be checked in case it is required to properly complete the circuit to the solenoid.

N3/1 in the schematic is the LH module, which receives a signal from the starter so it knows when the engine is being cranked, so it can run the fuel pumps. This receives the starting/cranking signal but is otherwise not involved in the major current flow to the starter; note the smaller wire size to the module.

I'd try bypassing the NSS next (shorting the sockets) to see if that cures it, if so, you need a new NSS. If not... ignition switch is looking more likely.