Went to start my vehicle today and had a complete loss of electrical power when I went to start. Power locks open fine before I tried to start, I breifly saw the insurment cluster lights turn on when I turned the key, but as soon as I hit the staert position all electrical power goes out. I heard a small movement sound but it didn't sound like the engine fully turned over when starting before the power was lost. No light, no locks, key is locked out from turning. The car is a 2006 C350 4-Matic, Canadian spec. It was sitting outside for a bit over 8 hours, about -20˚C for an hour or two at the start but more like -5˚C for the rest of the day. Battery was replaced just a couple months ago.

This feels like a blown fuse to me, I did a quick visual inspection of 52, and 57 but didn't see anything. Will need to bring my multimeter tommorow. I would assume this was some sort of master fuse issue but I can't find any master fuse listed. Any suggestions of what to look at?

 

i would start by checking the battery voltage. (I know it is a relatively new battery, but defects are always possible.) If the battery is OK, check to be sure you don't have a loose or corroded cable.

If you didn't install the battery yourself, you cannot rule out incorrect installation. Check to be sure the battery is securely held to the battery mount. If your car is like mine, the battery is held in place by a clamp positioned at the bottom of the battery. It is somewhat difficult to reach and the installer may not have tightened it sufficiently. If the battery moved because of a loose clamp, the battery may have been damaged.

I don't think there is a master fuse for the entire car. On my car, there is a power distribution block next to the battery. It has several fusible links in it. Perhaps one of the fusible links blew.

Distribution block with cover removed.

The slightly larger center post connects to the positive terminal on your battery. You should be able to check for continuity from the center post to each of the others. (Not all of the posts on my car are used. Your car may be different.) If you find you don't have continuity to one or more posts, that may be the culprit.

There may be other causes. These are just the first that come to mind.

Good luck.

 

Installed the battery myself and I am not sure about the fours, but the sixes don't have much room for the battery to move around in. I will check the distribution block.

 

Alright, current theory is a stuck starter relay. Since the starter relay cuts power to almost everything not part of the engine while the starter is running it would explain the loss of power else where. I will update with the outcome tommorow.

 

You taking nonsense about the starter relay. It does nothing but supply power to the starter. Do what Kevin says. Battery terminals are either loose or your battery is dud!

 

Tried again to start this morning. Nothing. Battery reads 11.98V. Bit later try again, still no power. Poke the fuses pre-fuses with the Multimeter as suggested, they all read good. Starter relay shows only connection between controlling contacts. Get back in and I see lights on the dash. Still no clue why this happened, but it is running now. Want to figure this out before it happens again. My logic on the starter relay was that something interrupts power to most of the vehicle when the starter is running. I figured that must be stuck somewhere. Relay seemed like a good choice for the controlling component since a SPDT can do it without needing an extra power.

 

Your voltage is a bit low. My car reads between 12.4 and 12.6V before I start it in the morning. It is my understanding that starting the car in cold temperatures require more battery power than on more temperate days. Your first post indicated that it was significantly below freezing when the this problem appeared. (For those of us in the southern portion of the U.S., a day with -20 degrees Centigrade/-4 Fahrenheit temperatures is a rare event.)

Do you have the ability to connect the car to a trickle charger overnight? If you can, connect the charger and check your voltage in the morning before starting the car. If the voltage is higher than 11.98 and the car starts more easily, you may want to focus on the battery and charging system as the problem area. You can display the voltage on the center screen of the dash and monitor what is happening. When the car is idling, the voltage should be about 13.8. When you are accelerating, the reading should be around 14.4. If you aren't seeing those levels, its possible that your alternator is on the way out and not charging the battery sufficiently.

There may be other issues, but this is what comes to mind.

Good luck.

 

The battery should never be below 12.0V ever when charged. Sounds like your battery is dead or dying. Yes I know it's supposedly a new one, but this still doesn't sound right.

Did you install a genuine MB battery?

My understanding is that a fully charged battery in good working condition should be at least 12.4V.

 

11.98V vs 12.00V is within multimeter accuracy. A little low, but it was sitting overnight in the cold and low temperatures do cause battery drain. 12V is nominal, meaning that a partially discharged battery will average close to 12V. I went to pull OBD II codes before I turned it off tonight, no faults were reported. I measured voltage as 14.0V at idle and 12.4 to 12.6 after engine off. Battery is aftermarket, mid range from a known Canadian brand that wouldn't be able to sell anything if they all failed in the cold. While it is harder to start in cold weather, a lot of that comes from the oil thickening. Up this far north -40˚C/-40˚F happens most years and so thinner oil is typically speced. The reason I don't think it was the battery is that all the other electical systems were not working afterwards. Sure the battery failing and being unable to turn over the motor would make sense, but 12V should be way more than enough to get the computers going.

 

No dash lights.. you need to try your spare key if you have. When this happens again look at live data and see if terminal 15c is active.

 

No dash lights, no interior lights, no power locks, nothing. I tried both keys when I went to start in the morning, no difference between them, both worked when the vehicle regained power. I will have to figure out where the actual terminal wire is and poke it with a multimeter, only way it looks like I will be getting live data.

 

Connect DAS and you will see

 

Happened again and it looks like I may have figured out the problem now. This time it happened twice this time while in a heated garage. First time power goes out when starting, then some lights on the dash board slowly light up and maybe 30 seconds later power is restored. I tried again, this time waiting with the key in position II for a couple seconds before trying to start. Engine does not start, electrical power is lost. A sound like a hard drive trying to spin up then losing power every couple seconds is audible behind the audio unit. Multimeter has trouble reading the voltage from the jumping connector on the prefuse box to the ground point on the car frame, giving me 3.5 to 5 V readings, I try the battery itself it gives 12.14V, battery negative to jumping connector, again around 5V. I wrote this off due to the jumping point not exactly being clean, I figured it was just a bad connection. I decide to grab my sockets and disconnect the battery then reconnect it to restart everything. Once I go to remove the positive terminal from the battery the car lights immediately turn on. It appears that there was either some salt or corrosion on the positive battery connector causing a connection problem. While the vehicle was sitting around, there was enough electricity able to get through to charge up the capaticors and run the electronics. Once the starter was engaged all that power was dumped and there was no power left to run anything in the vehicle. The first time connection was reestablished when I poked the teminals with the multimeter and moved the connector enough to get some clean metal to metal contact. Second time obviously more movement of the connector again. Went and bought some battery terminal cleaner for the connectors which really didn't look all that bad since they kept an entirely grey color rather than showing red rust.

 

First, keep it simple. Clean the battery terminals and cable ends. Then load test the battery. Check your grounds at the battery and at the car and not just the battery to body, but also body to engine or starter.