Mercedes-Benz-diesel P0300 OBD2 Check Engine Light Cause & Repair Info for Powertrain Trouble Codes.
Repair Information, Analysis, and Likely Causes for OBD-II Trouble Code P0300 - Random / Multiple Cylinder Misfire Detected|
The OBD Diagnostic process is preformed by your cars onboard computer system
using sensors located throughout your car's engine, drive train, chassis, body,
and network communication systems. Some trouble codes indicate real
problems with your vehicle and some indicate faulty sensors,
see Cause and Repair Info Below.
Note: Site Instructions Below
P0300 - (ASE)|
Ignition System or Engine Misfire
DTC Description: Random / Multiple Cylinder Misfire Detected
The random misfire Diagnostic Trouble Code (DTC) indicates multiple cylinders are misfiring or the Powertrain Control Module (PCM) cannot identify which cylinder is misfiring, and the Malfunction Indicator Lamp (MIL) is illuminated. A misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause. The misfire detection monitor is designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred, but in this case it can't determine the specific cylinder or cyliners that are misfiring.
Historically the most basic causes for misfires are lack of spark or an imbalanced fuel air mixture. If the misfires seem random or non-rhythmic the cause is more likely fuel. If it seems like there is a consistent, rhythmic, occurrence then its more likely caused by lack of spark. The same cylinder or cylinders are misfiring. This consistent rhythm could also occur if the issue is caused by individual injectors.
Listen to the engine to see if you can determine if its missing in a pattern or more sporadically missing. If its in a pattern, you can eliminate many of the broad causes for misfire and focus more on those specific to individual cylinders, or vice versa.
Ignition System Fault Affecting Two or More Cylinders:
-- Faulty Ignition coil, spark plugs, or Ignition wires.
-- Ignition Control (IC) circuit intermittently shorted to ground
-- Erratic or Interrupted Camshaft Position (CMP) or Crankshaft Position (CKP) sensor
Fuel Metering Affecting Two or More Cylinders:
-- Low Fuel, less than 1/8 tank, or out of fuel.
-- Fuel filter plugged, dirty, causing low fuel pressure.
-- Fuel pressure regulator (leaking, malfunctioning, etc., causing low or high fuel pressure).
-- Fuel pump (weak, check valve leaking, etc.), causing low fuel pressure. => Check Fuel Pressure
-- One or more leaking, contaminated or sticking fuel injectors => Blocks or reduces fuel flow
-- Fuel supply line restricted => Check for dents in metal tubing or kinks in rubber tubing.
-- Fuel Rail Pressure (FRP) sensor (incorrect reading).
-- Fuel supply contaminated
-- Evaporative Emission (EVAP) system, or EVAP canister is full or saturated
Air Leaks allow excess air into the Air Intake:
-- Positive Crankcase Ventilation (PCV) system (leak, valve stuck open, etc.)
-- Exhaust Gas Recirculation (EGR) valve stuck open, or tube, gasket or diaphragm leak
-- Blocked Exhaust Gas Recirculation (EGR) passages
Air Measurement Failure:
-- Mass Air Flow (MAF) or Air Flow Sensor (AFS) sensor contaminated, damaged, malfunctioning resulting in false air flow readings.
-- Faulty Manifold Absolute Pressure Sensor (MAP)
-- Incorrect voltage from Heated Oxygen Sensors (HO2S)
Base Engine Problem:
-- Mechanical problem effecting two or more cylinders (broken rings, leaking valves, bent push rods, etc.)
Note: On the first trip that the misfires are detected the Malfunction Indicator Lamp (MIL) will flash on and off. On subsequent trips the light will remain illuminated.
Also Note: if this is an Exhaust Gas Recirculation (EGR) issue, one or more Exhaust Gas Recirculation (EGR) passages may be blocked or partially blocked. If this is the case the Misfire Detection Monitor will indicate the Exhaust Gas Recirculation (EGR) port to check for possible blockage.
- Please note the list of automobile manufacturers at the left edge of the screen.
The currently selected ODB code is for the Mercedes-Benz-diesel family of autos. The codes for any
particular vehicle make and model will be found under the manufacturer family, i.e.
Dodge and Plymouth are part of the Chrysler family of cars and trucks.
- Also notice that just to the right of the manufacturer family list is a short group
of OBD II codes. The highlighted Mercedes-Benz-diesel OBDII code P0300 in this list is the currently selected code,
and the information on this page pertains to trouble code P0300. The other codes in the list
above and below this code are OBD codes some of which may be related to the current
fault code and can be navigated to directly.
- Need to look up additional OBD II Trouble Codes, use the search box. Enter the 5
character trouble codes in the search box and submit the search. You can repeat the
search as many times as you need, one diagnostic code per search.
- Don't assume a particular OBD2 code means the same for other auto manufacturers as
there are many manufacturer specific codes in use.
- If your trouble codes are for a different auto family, select that vehicle series
before searching for the diagnostic codes because not all OBD codes used by one
manufacture are used by the other manufactures. The search only looks at OBD codes
valid for the currently selected manufacturer family.
- If your automotive family is grayed out, the current OBD code, P0300,
is not among those used by the current manufacturer. You can click un-gray at
the bottom of the auto family list and then select the manufacturer for your vehicle
before searching for your fault codes.