DomiNOOCH

Okay....this should be an easy one for those of you who know a lot more about these technological marvels than I do....for about two weeks now, the car won't start on the very first attempt. I realize that prior to starting there are two pneumatic pumps that energize; they both seem to be coming from the trunk area and one pumps when I turn the key-fob to the on position (not start) and the other when I step on the brake. Using key-fob only (key in on position I wait for pump to stop) car won't start with first try; I step on brake pedal wait for second pump to stop and car starts right up. For the balance of the day the car starts first time every time. Everything else (lights, locks, trunk easy close, windows, seats) works as normal. All batteries are new (including key fobs) and I get no messages in dash. Car is always on tender and I hear no leaks anywhere in or around the car. PS: car behaves exactly the same way when I switch to keyless go. Any thoughts would be greatly appreciated.!! (2003 MB SL500 w/ 60K)

Rudeney

I seriously doubt this has anything to do with the pumps. The two pumps you may hear running in your car are PSE pump in the trunk and the SBC pump under the hood. The PSE (pneumatic system equipment) pump provides air pressure to operate various things like the trunk and door locks, locks for cabin rear stowage compartments and the glove box, plus the lumbar adjustments on the seats. The SBC (Sensatronic Brake Control) pump replaces the vacuum booster for the car's brakes and just pressurized brake fluid in its reservoir.

The car will start just fine with or without these systems working, though you probably don't want to drive it if SBC is malfunctioning because braking efficiency is GREATLY reduced and pedal effort is GREATLY increased. My guess is that maybe you have a weak battery. Note that the starter is powered by the battery under the hood. Another I would start b checking it's voltage at rest and when turning the key to start. If it's low (below 12.5v) then it may be time for a new one. If not, and voltage does not drop at all when turning the key, then it's not a voltage supply issue. It then could be something like a bad EIS (ignition switch) or even a misaligned shifter linkage so the car is not recognized as being in park.

DomiNOOCH

Rodney,

Just replaced both batteries 5 months ago with Advanced Auto, Auto Craft batteries (per your recommendation). In spite of that I took your advise and checked voltage on the starter battery and recorded the following; voltage @ rest 12.87v, voltage with key in on position 12.87, voltage @ startup 11.25, voltage w/car running 14.25v.

Is this normal? With that kind of voltage drop @ startup could the battery need replacement already after 5 months?

Rudeney

Those readings sound good. When you turn the key to crank the first time, and it doesn't, what's the voltage at that point? If it still drops, then I think it's a bad starter.

Oh, wait - I assume you mean that it does not crank on the first try. Is that correct? You turn the key but the start does not engage and the engine does not crank? If that is incorrect and the starter does engage and the engine does crank, but it does not fire and run, then it's not battery voltage, but a fuel delivery problem or CPS failure

Tirgoman

If the ignition comes on and the dash lights up but the starters does not crank it could be the brake light switch, this will not let the starter crank unless depressed. Maybe your continued pressure is then letting it start on the second try, especially with the brake pressure pump running to make it easier to press the brake pedal. If the starter cranks but the engine does not start then it's an ignition problem but I doubt it.

bobterry99

If the crankshaft position sensor is faulty, then the engine management controller uses the camshaft position sensor as a reference for sequencing the injection and ignition systems. In doing so there is a 50-50 chance the engine will start.

That would explain an occasional failure to start on the first attempt but not for it happening consistently every time over a period of time.

DomiNOOCH

I suppose it's time for a quick update on my "first attempt" startup dilemma. First of all, thanks to all who provided advice/guidance and perhaps some of you may be interested in the following results. After considering bobterry99 advice I replaced the crankshaft position sensor (a $29.50 part) to no avail; it made absolutely no difference and the car still wouldn't start the first time with either the keyfob or the keyless go. Next step.....Tirgoman advised to replace the brake light switch which I did (a $21.50 part) with interesting results. The car starts up first time, every time with keyless go and foot on the brake pedal but still will not start first time with keyfob. As mentioned in my first post, after initial start up the car will continue to start each and every time, regardless of starting choice, all day. Obviously I elected to perform the two low cost repairs first, but now I'm afraid it's on to the more costly alternatives if anyone else has any ideas.

Tirgoman

OK, you're on the right track, it may not have even been the brake light switch, the issue can be that when the car sits if there is a vacuum leak the brake peddle doesn't depress enough to actuate the brake switch and the car thinks that you don't have your foot on the brake (for safety to not let it start and run into a wall-that old Audi thing), so after you start it once it does start after that. Try pressing on the brake peddle real hard and see if you can duplicate it. Of course when you replaced the switch it could now be in a position that you don't have to press really hard to actuate it. My wife had this on a 2015 C-300. I'd say you have a very tiny vacuum leak. Now the difference between it starting with keyless go and not with the fob, I guess I don't understand what you're saying. With keyless go you unlock the car with the fob in your pocket and then get in the car and press the starter button. Or are you saying you have to put the key in slot and then start it? You're getting there but I need more info. As for the vacuum leak, it's still there, you need some soapy water or a stethoscope (a cheap one from the auto parts store) and start at the brake booster and follow the hoses carefully inspecting each one or finding where it sucks the water into the line, probably at a fitting or a bad hose somewhere. I think there's a vacuum reserve tank also.

DomiNOOCH

What I am experiencing is I get in the car and try to start using the key fob only and I get nothing. I get in car without key fob (I leave the key in the house) and have keyless go card in my wallet, and step on the brake pedal (which I'm told is a must using keyless go) and push start button it will start first time every time (since I replaced the brake switch).

Tirgoman

Do you have keyless go only or also it function like keyless entry, where you get near the car, pull the door handle and it unlocks. If so and it unlocks the car then it points to the car not talking to the fob only when it's in the car, there's probably a module that does that. If keyless go is separate and it works with the card and not the fob then it has to be the fob. I'm not familiar withe card, interesting.

DomiNOOCH

I do have keyless go that also functions as keyless entry and the locking and entry feature works just fine.

DomiNOOCH

I've got good news and bad news !!! First the bad....in addition to all the repairs stated above, I also replaced the starter relay (a $19.50 part) to no avail. Now the good....I read somewhere of someone having the same problem as I and he was able to narrow it down to the keyfob not communicating with the EIS upon first attempt, then removing the key, reinserting it and the car started right up. Thought I'd give it a try and "BINGO" it worked. Can anyone out there explain why this would occur, what to do about it, and is there a simple repair I can perform to solve this dilemma once and for all. Many thanks for all your consideration !!

Blazeracer

Mine does that randomly probably once a day or so. It'll crank and crank and crank, then rumble for sec and shut off. Hit the key second time and it pops right off. I'm not going to chase down a million things that might be wrong. Whatever it is needs to break, then I'll fix it for good. Maybe.. I'm about ready to sell this damn thing. I'm getting more hydrauic failures than an english major in a trig course.

Tirgoman

Pretty simple, the fob had become unsynchronized with the cat, putting the fob into the ignition resynced the fob. Glad everything is now working. PS, sometimes you have to do this after replacing the batteries in the fob.

DomiNOOCH

[QUOTE=Tirgoman;7853011]Pretty simple, the fob had become unsynchronized with the cat, putting the fob into the ignition resynced the fob. Glad everything is now working. PS, sometimes you have to do this after replacing the batteries in the fob.

Resync the fob ????

DomiNOOCH

Tirgoman,

I think you may have misunderstood me. My point was NOT problem solved, mission accomplished!! I need to insert key (attempt to start..nothing), remove key, insert key again (attempt to start).....sometimes nothing, sometimes it will start.....if not remove key and try again.

Tirgoman

Now you've confused me. If you have keyless go you should be able to enter the car with the key/fob in your pocket and then push the starter button to start the car. If you pull out the starter button you can also insert the key and then start the car.
Sometimes you do need to actually insert the key to let the car talk to the key and re-sync them.
So what is the problem now?

DomiNOOCH

NO !!! keep in mind I have a 2003 SL500 (obsolete technology)....my keyless go is a card I keep in my wallet.....without card, starter button doesn't work....my car starts with either one or the other but not both. In other words I could leave key/fob @ home and travel with just the keyless/go card to start the car.