Skinnywater
Commander
- Joined
- Mar 7, 2002
- Messages
- 2,065
Re: Any Mercedes Benz Techs out there?
The ML has 4 02 sensors. Two before and two after the catalysts. The two prior monitor mixture, the two after monitor catalyst performance only.<br />Default of an mixture monitoring O2 sensor is a fixed map mixture or open loop. Open loop is a fixed rich mixture. I've never witnessed and believe its unheard of a malfunctioning O2 that will default to a lean condition. A lean condition will be caused by other means, then sensed by an O2.<br />However, once an O2 senses lean, what does it do?<br />Sends a voltage signal to the ECM to richen the mixture.<br />The O2 sensors aren't fuel sensitive. They are O2 and heat sensitive. <br />Again, any deviation of mixture out of range, rich or lean, sets a stored hard mixture code, freeze frame data and illumination of the MIL.<br />Mixture codes are undoubtably the most common I have to deal with, thanks to common failures of MAF sensors (Mass AirFlow Sensors.)<br /><br />The fact that no mention was made that a MIL (check engine) illuminated. And a negative report of DTC's in ME is a significant clue.<br />The emmisions warranty already exceeds thier generous warranty. Mercedes has made a major effort to protect the four very expensive catlysts. <br />The ME OBD2 is very sensitive to mixture faults and misfire faults. A restricted fuel filter or a loss in fuel pressure will set stored multiple misfire codes, permanently or temporarily set a MIL. This information weather a current fault or registered fault will be stored in in ME memory along with freeze frame data. <br />Freeze frame meaning, vehicle speed and RPM, # of fault occurence, # of trips since last fault, ambient air temp, engine coolant temp, throttle position, load and all adaptation figures and more.<br /><br />Back to the significant clue. Either the fault was one that isn't monitored by ME to set a MIL. <br />I.E. a brake locking up or the fault is in another system that won't set a MIL. <br />This significant clue, along with the previously mentioned California fuel, the Sierra Nevada and Cascade mountain ranges, complaints identical to JB's.............as sure as blown f44.....the 722.6 was going into overload protection.....slightly overheated it .......if worse....limp home was to follow......been there.....done that....<br /><br />Hence the method to my likely internet diagnosis.
The ML has 4 02 sensors. Two before and two after the catalysts. The two prior monitor mixture, the two after monitor catalyst performance only.<br />Default of an mixture monitoring O2 sensor is a fixed map mixture or open loop. Open loop is a fixed rich mixture. I've never witnessed and believe its unheard of a malfunctioning O2 that will default to a lean condition. A lean condition will be caused by other means, then sensed by an O2.<br />However, once an O2 senses lean, what does it do?<br />Sends a voltage signal to the ECM to richen the mixture.<br />The O2 sensors aren't fuel sensitive. They are O2 and heat sensitive. <br />Again, any deviation of mixture out of range, rich or lean, sets a stored hard mixture code, freeze frame data and illumination of the MIL.<br />Mixture codes are undoubtably the most common I have to deal with, thanks to common failures of MAF sensors (Mass AirFlow Sensors.)<br /><br />The fact that no mention was made that a MIL (check engine) illuminated. And a negative report of DTC's in ME is a significant clue.<br />The emmisions warranty already exceeds thier generous warranty. Mercedes has made a major effort to protect the four very expensive catlysts. <br />The ME OBD2 is very sensitive to mixture faults and misfire faults. A restricted fuel filter or a loss in fuel pressure will set stored multiple misfire codes, permanently or temporarily set a MIL. This information weather a current fault or registered fault will be stored in in ME memory along with freeze frame data. <br />Freeze frame meaning, vehicle speed and RPM, # of fault occurence, # of trips since last fault, ambient air temp, engine coolant temp, throttle position, load and all adaptation figures and more.<br /><br />Back to the significant clue. Either the fault was one that isn't monitored by ME to set a MIL. <br />I.E. a brake locking up or the fault is in another system that won't set a MIL. <br />This significant clue, along with the previously mentioned California fuel, the Sierra Nevada and Cascade mountain ranges, complaints identical to JB's.............as sure as blown f44.....the 722.6 was going into overload protection.....slightly overheated it .......if worse....limp home was to follow......been there.....done that....<br /><br />Hence the method to my likely internet diagnosis.
