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I have a 2011 E550 Cab. car has 80k on it and is well taken care of. Last week engine light came on. My indy pulled the codes and it showed both upwind O2 sensors bad. He mentioned it might be an alternator issue instead and reset the codes however didn't have time to test the alternator. I drove the car for the entire next day and she was all good. Started car this am and after putting in reverse she almost died and the engine light came back on ( not sure if it's the same codes or not) . Then the car started revving on its own. between 1k and 2.5k back and forth slowly. Couldn't get it to idle correctly and obviously can't drive it with it changing engine speed on its own. Also sounds like its missing. After this the warning comes on that the ESC system is not available / disabled.
The car has a AGM Interstate battery that I installed 4 years ago. Smartcharger said battery was borderline good (80%) and its taking a charge now.
I'm obviously nervous about taking it to dealership however not sure if my local indy has the expertise to diagnose / handle. I think this all this leads up to a bad alternator however I just don't know. I think that the car was acting wonky right before I replaced the battery last time just can't remember the symptoms.
A bad alternator should give a Red or Amber Battery light on the dash (in most cars anyway). Check your manual for the exact warnings to look for when a battery or alternator is bad. Then confirm you have a full charge on your 12V battery. Not sure what SmartCharger you're talking about, but there should be some indication that the battery has achieved full charge. Then, perhaps disconnect the negative terminal of the battery for 10 minutes to completely kill any power on the car. This may reset some warning systems, check engine light (CEL) for one. Then reconnect and see how it behaves?
Last edited by SilberGrau57; Jan 26, 2020 at 09:52 PM.
Of course best to pull codes. If you have a multimeter general rule: set to 20V DC and connect the leads to the battery should read around 12 volts or so. Start engine it should be around 14 volts, turn on headlights, radio, heater, etc. should be around 13 volts if not, could be alternator (part # 0131545602 or 013154560280). 02 sensor can cause misfire, hesitation, stalling.
2010 E550 coupe,2005 porsche ca 911,04 subaru outback,94 Harley FXSTC
If you have codes for both front ego sensors ,more then likely there a fuel control system malfunction.Very rare for two sensors fail at same time.You need to have tests done per shop manual diagnosis chart.You could have a vacuum leak ,fuel delivery ,fuel control sensor like MAF sensor that can cause these codes.If in fact you have two sensors that are doing same job except opposite sides of engine tests fail,then you need to look for a short or open circuit causing the failure.
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