DaveG129

Hi,
New member here.
I just picked up a 1999 500SL. It won't crank or start. I get dash lights, but no crank, and no solenoid click. Battery is new and strong. I don't see any anti-theft message on the dash. I connected two different OBDII readers, both came up error and did not connect. All this leads me to believe the ignition switch is bad, and the ignition is not switching on.
Have I missed something? (Before I jump in and replace the ignition switch.)

Thanks very much!

Kebowers47

Acts like it is some where in the 'starting systemS'. It can be the actual electrical contacts in the 'ignition switch' --the indicator lig
lights and gauges are supposed to come on in the 'RUN' position; or ---anti-theft module, starting authorization module (SAM units), gear selector problem, brake switch, etc. A bad fuse, relay, module, 'code in a module' and probably several other possibilities. The 'keyless start' system is a known troublesome system. Even a defective contact in one of the exterior door handles. Either a Dealer or GOOD Indy with electrical system diagnosis capability. Just looking and replacing parts is NOT advisable as it can be both frustrating and frightfully expensive.

Good Luck

bobterry99

I'd check to see if the starter control relay is energizing. While someone turns the key I would listen for its contacts to make an audible "click" as they close. The relay is located behind the fuses in the main fuse box under the hood.

anrualrize

Check if your car has an alarm and immobilizer, if so, in addition to the starter relay, you must ensure that contacts 4 and 5 of the alarm are closed and that they are in the alarm center (ATA)

On the other hand, if your car is automatic, check that the parking switch is working, because if it is not closed, it will not start either.

Sorry for my English, it's not my mother language.

Floobydust

The ignition switch would be low on my list as a cause. As stated above, there could be an issue with the neutral safety switch - try starting it with the transmission in neutral instead of park. If your readers are relatively new (e.g., they support all current protocols) and you tried with the key on (dash lights on), then no communication on the OBDII connector makes me suspicious of an ECU or CAN bus fault. The engine does not have to be running to establish a connection on the OBDII connector.

Lastly, try locking and unlocking the car from the door with the mechanical key instead of the IR remote. On a USA/Japan R129, the mechanical key with arm/disarm the ATA/DAS. Your IRCL module may have failed so it is not authorizing a start condition.

bobterry99

I'm sure the original poster is long gone, but there are a couple points worth noting.

Cars fitted with the 722.6 electronically-controlled transmission haven't got a neutral-safety switch, so that pertains to this 1999 car. What it has is a signal from the transmission ECU which reads the position of the shift lever via a position switch outputting a voltage-coded signal.

Also, 1998 and newer SLs haven't got an IRCL module, as that is the year they switched from infrared to radio frequency remote locking. For those later years the Drive Authorization System and remote locking are integrated into a single module located behind the instrument cluster.

Floobydust

Yes, indeed, probably so.

My bad, I thought that 2000 was the first year for the M113/722.6 drive train. Even with no mechanical NSS per se, at least on the G wagen 722.6, I have seen fluids having been spilled into the shifter assembly causing issues.

As for the module, yes, but I believe MB went to a dual mode system for the later cars - radio for door locks and IR for the windows open/close convenience feature (for safety, I think). My 2000 has the IR sensors on the door handles. Indeed MB describes the 129 820 37 26 module as " 1996-02. Infra-red, all" That's why I refer to it as the IRCL.

I have been digging into this system on my 2000 because the remote locks will lock, but not unlock (most of the time) even though the parking lights flash for both. I initially got a "door receiver, open or shorted" error on the module which I cleared, but nothing since. Sometimes pressing the open button on the key will actually lock the car. And the trunk is a no-go. The system seems to be just possessed. Sadly, 129 820 37 26 is NLA from MB or anywhere.

If you have any thoughts, I would appreciate it.

bobterry99

A pair of signals from the DAS module control the vacuum pump for purposes of locking and unlocking the vehicle: SN1 Out and SN2 Out. The Electrical Troubleshooting Manual (ETM) inaccurately documents these, and what follows is conjecture which I think is probably correct but you might confirm for yourself.

The response of the parking lights to locking commands is controlled directly from the DAS module. Fortunately you indicate the lights respond correctly, so this confirms that at least one function of the DAS module performs reliably.

When either the lock or unlock button on the remote is pressed, the voltage on SN1 Out goes to c. 0 VDC. The nature of the signal on SN2 Out dictates whether the pump locks or unlocks the vehicle. For one case (lock?) it is a single DC pulse, and for the other it is multiple pulses (three?). In the case where your PSE responds incorrectly to the buttons on the remote I presume there is an issue with the production of SN2 Out in the DAS module, wiring, or the processing of SN2 Out in the PSE pump. Personally, I would monitor SN2 Out using a multimeter if the locking issue can be reliably reproduced; otherwise, I might construct a simple electronic circuit to do the monitoring continuously.

You may want to view the wiring diagram for DAS and the PSE pump, and as you may not have this, here is a link to a small download of all R129 wiring diagrams: R129 ETM 64. The diagrams install and uninstall just like a typical Windows program. When you are viewing a wiring diagram you pan around by pressing the left mouse button and dragging it. To zoom in and out you use the page up and page down keys on your keyboard.

Floobydust

Thank you very, very much for the explanation and the the link to the schematics!!! I have the R129 service DVD but it is an old copy and won't run on my current laptop. When I get home tonight I will download from your link. That will be extremely helpful!!

I can monitor the signals with my portable digital scope - that way I can see the pulse train also. I always thought the PSE on the R124 worked like the one on the W124 - one control line that "floats" and then gets grounded or tied to +12 to lock/unlock. Since the PSE is interpreting a pules train, do you think the problem may be with the PSE?

Thanks again!!

Floobydust

Do you by any chance have a 32 bit version of the .exe?

Thanks!

Tonysl1234

I have a sl500 1991 32bit amg auto

Not any issues to speak of, up to now

So

Battery fine, go to start the car,

All the lights come up, turn the key , no crank, nothing, fuel pump, fine, suggested to look at the inhibitor, , if we bridge the inhibitor, car fires up fine, so we replaced the Mercedes-Benz Inhibitor and Reverse Light Switch – 0005454906, Located on the transmission housing, no go , same fault ,



Any suggestions

Ignition switch ?

Thanks tony

DaveG129

Thought I'd update as I finally solved it! I'm now motoring around blazing hot California with the top down in a triple black SL500 with 18" AMG wheels. Thank goodness the AC is ice cold!

Turns out the Engine Control Module was bad. It is the slide in black box on the passenger side electronics box. It has three fuses on top. Part number A 020 545 54 32 GM
Before I replaced it, I did the following. Some of it unnecessary in hindsight.

Replaced starter motor. Really a pretty easy job. Turn the steering wheel to the full left to give you clearance on the steering gear when removing starter. Wiggle it out towards the front of the car. It was handy to have a 20" 3/8 drive extension for the upper starter motor bolt, not sure it could have done it without the extension.
Sent the silver alloy Engine Control Unit A 026 545 69 32 to CarComputerExchange to 'fix' it. Turns out it wasn't the problem, $299 peace of mind. I see online they have some mixed reviews, my experience with them was very good. Fast turnaround, good communication. I would use them again.
Reconditioned and charged battery, it was new in May 2000 but had been sitting.
Replaced the K38 relay. On my 1999, it's in the electronics box in the engine compartment, drivers side, closer to the firewall that the fusebox. You have to take the fusebox cover off to see it. - Changing it made no difference. I was able to jump the terminals in the socket and get the starter to spin, but engine did not catch.
Came across The R129 Co in England. They offered email diagnostic, suggested it was the ECM, so I bought one from them. Yes, it cost more to get it to CA from England, ($80 product and shipping), and I could've ordered one from eBay, but these guys helped me out immensely, and were spot on correct on the diagnosis.
Support the people and companies that help you! I'm absolutely going to buy as much as possible from them, even if it costs a couple bucks more in shipping, etc.

I hope this helps someone, have a great day!

Floobydust

Glad all is working. A 020 545 54 32 is what MB calls the "base module" which is essentially a power switching center that is similar to the older Over Voltage Protection (OVP) relay, but more complex. I should have thought about that as a cause.

Floobydust

Just one more update -

Thank you to bobterry99 for all of your help! I did some snooping and it looked like the PSE was getting the signals that it should, so I replaced the PSE pump with one off of eBay, and viola, locking problem fixed!

Floobydust

FYI, I did a postmortem on the old PSE pump and found corrosion on the PCB at the power connector. Clearly water leaked in there during the winter it spent outside.

TAR

Thank you for your postings, especially the description of who finally provided you with the analysis to remedy the problem. It has now been two years since you posted your msgs. Has the ECM replacement you completed continued to remedy the problem?