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GMC/General-Motors P0305 OBD II Check Engine Light Cause & Repair Info for Powertrain Trouble Codes.

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P0305 OBD-II Trouble Code, Misfire Cylinder No.5 - GMC/General-Motors
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GMC/General-Motors P0305 OBD II Check Engine Light Cause & Repair Info for Powertrain Trouble Codes.
Repair Information, Analysis, and Likely Causes for OBD-II Trouble Code P0305 - Misfire Detected (Cylinder No.5)

The OBD 2 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
Trouble Code:
System:
Subsystem:
 P0305 - (ASE)
 Powertrain
 Ignition System or Engine Misfire

DTC Description: Misfire Detected (Cylinder No.5)
Analysis:  The misfire detection monitor is designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause.
Process Synopsis:

The Malfunction Indicator Light (MIL) will blink once per second when a misfire is detected severe enough to cause catalyst damage. If the Malfunction Indicator Light (MIL) is on steady state, due to a misfire, this will indicate the threshold for emissions was exceeded and cause the vehicle to fail an inspection and maintenance tailpipe test.

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. Since only one cylinder is misfiring, an inconsistent rhythm would be more like bursts or stuttering which indicates its more likely a fuel issue.

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 firing individual cylinders, or vice versa.


Likely Causes:

Ignition System Fault Affecting Cylinder No. 5:
-- Faulty spark plug or Ignition wire affecting only one cylinder. (Replace spark plug & plug wire, check spark at plug)
-- Faulty Ignition coil (Some models have a Coil Fuse) => Check Spark
-- Erratic or Interrupted Camshaft Position (CMP) or Crankshaft Position (CKP) sensor
Fuel Metering Affecting a Single Cylinder:
-- Low Fuel, less than 1/8 tank, or out of fuel.
-- Leaking, contaminated or sticking fuel injector => Reduced fuel flow
-- Fuel pump (weak, check valve leaking, etc.), causing low fuel pressure. => Check Pump Relay & Fuel Pressure
Air Leaking into the Intake Manifold:
-- Positive Crankcase Ventilation (PCV) system (leak, valve stuck open, etc.)
-- Exhaust Gas Recirculation (EGR) valve stuck open, or tube, gasket or diaphragm leak
Base Engine Problem:
-- Low Cylinder compression (Check compression & compare to other cylinders)
-- Mechanical problem effecting only one cylinder (broken rings, leaking valves, bent push rods, broken rocker arm, etc.)

Warning: Misfires bad enough to set the Malfunction Indicator Lamp (MIL) will damage your catalyst system over time if not repaired.

Site Instructions:

  1. Please note the list of automobile manufacturers at the left edge of the screen. The currently selected ODB code is for the GMC/General-Motors 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.
  2. Also notice that just to the right of the manufacturer family list is a short group of OBD II codes. The highlighted GMC/General-Motors OBDII code P0305 in this list is the currently selected code, and the information on this page pertains to trouble code P0305. The other codes in the list above and below this code are OBD 2 codes some of which may be related to the current fault code and can be navigated to directly.
  3. 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.
  4. Don't assume a particular OBD2 code means the same for other auto manufacturers as there are many manufacturer specific codes in use.
  5. If your trouble codes are for a different auto family, select that vehicle series before searching for the diagnostic codes because not all OBD 2 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.
  6. If your automotive family is grayed out, the current OBD code, P0305, 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.
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