Charging woes -- battery or current sensor?
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Joined: Jan 2020
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2013 C300
Charging woes -- battery or current sensor?
Hello! I recently purchased my dad's 2013 C300 from him. It has about 32,000 miles on it. Since I've had it, the ECO indicator on the dash has always been amber and didn't seem to do anything. Yesterday when I started the car, I got the red battery display on the center HUD. The only noticeable difference is that ECO is completely disabled (no longer displayed on the HUD) and the eco switch is out. Radio, A/C, lights, heated seats and rear defroster all operate normally. Here is what I checked so far:
- Accessory belt looks fine.
- Starter battery seems strong -- the car cranks fine
I checked the "vehicle data" menu in the service menu for the voltage and current draw. Here is where things start looking wonky. With the vehicle off, it reported voltage at 12.7V and draw at 0.00A. After turning on the car, the display remains at 12.7V/0.00A for my entire drive. I have yet to dig into the trunk compartment with a multimeter to check the consumer battery, and haven't checked if the starter battery is being charged or not yet either but plan to.
Does this sound like the consumer battery being dead or maybe the current sensor on the battery? Where is the voltage sensed for the "UB" vehicle battery display?
- Accessory belt looks fine.
- Starter battery seems strong -- the car cranks fine
I checked the "vehicle data" menu in the service menu for the voltage and current draw. Here is where things start looking wonky. With the vehicle off, it reported voltage at 12.7V and draw at 0.00A. After turning on the car, the display remains at 12.7V/0.00A for my entire drive. I have yet to dig into the trunk compartment with a multimeter to check the consumer battery, and haven't checked if the starter battery is being charged or not yet either but plan to.
Does this sound like the consumer battery being dead or maybe the current sensor on the battery? Where is the voltage sensed for the "UB" vehicle battery display?
Thread Starter
Newbie
Joined: Jan 2020
Posts: 2
Likes: 0
2013 C300
I took a quick look in the trunk again, and pulled out the spare tire. There's a wiring harness that goes from inside the battery box (i didn't fully remove the cover, just looked at the cables) down to a small device mounted under the spare tire. The cable to this box was frozen to the bottom of the trunk well from some crud that was on the tire presumably (had a flat last week that was replaced). I'll try to snap a picture to get the part number off the box later to figure out what it is unless someone has any idea. I did snap a picture of the label on the negative lead and it does not appear to be one with the current sensor built in (and is super clean), unless its burred further in. When I have a chance to get the cover off I'll check more.
