yellafella

Good morning all,

I wanted to share a fix that only took the dealership 24 days to find and fix.

Original issue:

• Car wouldn't start but vehicle had power (new primary and secondary battery installed 1 month earlier)
• Locks, rear hatch, lights and radio all worked but the starter would not engage to turn the engine. Turn the key and no action except the throttle body actuators

Resolution:

• Dealership diagnosed and replaced starter
• Vehicle worked for 1 day before issue reappeared
• Dealership towed it back and worked on for 24 days and found the root cause

Root Cause:

• Master technician finally traced the issue by examining the wires from the battery outward
• The cable from the jump points (the points in the engine bay used to jump start the car) that connects directly to the starter was shorting out and sending too much voltage --> This caused the starter and the replacement starter to burn out

I'm so glad to have my car back and that they were thorough enough to find out the root cause of the problem. Luckily, I had a brand new loaner to drive around for almost a month. Now I don't have to worry about my wife and son getting stuck somewhere.

efzauner

The explanation makes no technical sense. The starter gets full battery voltage thru the starter solenoid. How can a short cause "too much voltage". I would like to see the explanation on your repair work order.

marc hanna

Sounds like a strange explanation to me too.

josworth

It would make sense if the starter was getting full amperage, but not voltage.. The 14 or so volts a fully charged battery sends would not burn out a starter... but ... if there was a short that sent the full amperage from the battery to the starter that would burn up the starter motor... and if that was the case the OP is very lucky the starter acted as a fuse. That kind of short could very easily also start a fire.

I too would like to see more information on this. May have to inspect some wires during the next service, just to be safe.

efzauner

Your explanation makes even less sense and is totally ignorant of ohms law.
A battery is a voltage source, not a current source. A load will draw current depending on ohms law. A starter motor does draw huge currents, 100 amps or more, and will burn out eventually if you turn it over way to much. But you will probably kill the battery before.


when the starter is activated, you basically have a direct path between the battery positive, thru the starter solenoid (this is just a big switch) to the starter motor coils, to ground, then back to battery negative. Very low resistance, huge wires, no fuses. If there is a short from positive to ground somewhere there may be smoke and fire. Yet not always. I had a short thru the alternator in another car and it is surprising how much current the large wires can handle.


So again, all these explanation make no electrical sense at all.
Either the dealer is trying to bamboozle you with tech talk, or they are trying to explain something complex in layman terms, and have failed miserably. Hope its the latter!

marc hanna

efzauner is correct. The battery doesn't push amperage, the starter draws it. The battery pushes voltage so to speak.

something fishy going on.

efzauner

It could very well be that the starter was engaged for a long period of time due to a short, but that this took days to diagnose is puzzling.

marc hanna

Well, these starter systems are a little more complex, not the traditional simple electric system, but rather an electronic system. So they were probably searching around to see if some other electrical or electronic device was blocking the start sequence.

efzauner

Marc
actually from the original description , the problem is isolated to the 12v power and ground system from battery to front jump terminal to starter.


Looking at the wiring diagrams from ALLDATADIY ( I also have MB Star system data base) there are electronics, but ultimately there is one module that sends a 12 volt signal directly to the start relay in the front right fuse/relay box. This relay then powers the starter solenoid (which is an integral part of the starter) to close contact and power the starter. The solenoid has a direct connect thick wire to the battery/front jump terminal. Return is via chassis ground. No fuses here! The wires are well protected, very rugged and in my 40 year home mechanic experience rarely cause a short. Most problems would be corroded terminals causing an open or high resistance.

Conceivably there could have been a short in the fuse/relay box wiring that caused the starter relay to close intermittently, or stay closed longer, causing the starter to activate. There may not be any damage to the control wiring because the electronics module is normally protected. But it would be very obvious that the starter was engaged. Excess use would cause it to overheat and burn out. Remember that the solenoid is either open or closed, there is no way to send only partial power to the starter. The other possibility is that a short would cause the starter relay to malfunction and NOT send power to the solenoid. But this could hardly cause the starter to burn out.
So unless the OP has more detailed info, such as part numbers that where changed, I am halting this wonky wild goose chase... Lucas electronics in my first drive, an Austin Marina, comes to mind!
Have a great weekend!
I am going to pressure wash my R350 engine... and that's all because I still don't have plates... bloody mess at quebec licence office.

marc hanna

Your assessment of the situation sounds fair. I haven't dug into the starting electronics on these because I've never had a problem with on e before.

Hopefully the OP can update us.

ski518

Yeah, I developed FoMoCo's Electrical / Electronics Courses, plus have a BS in Auto Engineering, taught Electrical / Electronics to all the ASSET instructors in North America and at Weber State University. mmm, one could say these guys installed a starter on a vehicle, which may or may not have needed one. I have no idea what fixed your vehicle, but a short on the rock & roll side of the starter circuit may blow a fuse-able link, but will not damage the starter. If the starter was damaged, something else caused it. Again, don't know what fixed it. I would have to speak to the Master Tech. Bad terminal? t could have been the ignition switch/module? This is weird timing, but I should share with you. I visited a friend's shop two nights ago, I see an ignition switch / module, (like yours) , on his bench and it was replaced to resolve the same concern you had. Now, I must say starter motors "burn out" due to age and they will go bad over time. So, it's replacement may have been warranted.

bbspoolside

The cable from the jump point down to the starter are a known problem for corroding inside the plastic cover and not carrying full voltage to the starter motor. The result is either a slow crank or no crank at all. Ask me how I know lol

Yemiii

Just went through the starter saga

can you guys post how often have you replaced your starter?

mine so far is 3rd starter in 10yrs

we have other brands in family fleet at the same period and usage is basically equal ..never starter issues

efzauner

wow, Nice to resurrect old threats. And wow, did I spend time researching this one back then!

I have never changed a starter in what.. 62-16... years of driving.