P0300
P0300-MULTIPLE CYLINDER MISFIRE
For a complete wiring diagram, refer to the Wiring Information.
Theory of Operation
The misfire detection monitor software strategy in the Powertrain Control Module (PCM) is designed to detect an engine misfire. The PCM uses the Crankshaft (CKP) and Camshaft (CMP) sensors to determine when an engine misfire event is occurring and determine individual misfire events by monitoring the crankshaft rotational speed. A misfire is nothing more than a lack of combustion, which can be caused by poor fuel quality or metering, low compression, lack of spark or unmetered air entering the engine. On engines equipped with Exhaust Gas Recirculation (EGR), another possible cause is unwanted EGR flow. In the case of multiple cylinders misfiring or the PCM not determining the specific cylinder misfiring, P0300 Multiple Cylinder Misfire will set.
- When Monitored:
Any time the engine is running and the adaptive numerator has been successfully updated.
- Set Condition:
The threshold to set the fault is application specific; it is tied to the level of misfire that will cause emissions to increase to 1.5 times the standard or in some cases 1%. It is always a two trip fault above the calibrated RPM. It takes one fail to set a Pending Fault and two trips to set the MIL. Three good trips to turn off the MIL.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. PCM Pre-Diagnostic Troubleshooting Procedure.
Diagnostic Test
1. ACTIVE DTC
1. Diagnose and repair any other active component or circuit DTCs before continuing with this procedure.
2. Turn the ignition on.
3. With the scan tool, select View DTCs. Copy DTC and Freeze Frame information.
4. With the scan tool, erase DTCs.
5. Operate the vehicle under conditions similar to which the DTC was set.
6. With the scan tool, view the Misfire Monitor to see which cylinders are effected.
NOTE: It may be necessary to test drive the vehicle within the DTC monitoring conditions in order for this DTC to set or to show misfires on a particular cylinder.
Are there excessive misfires shown or is the DTC pending at this time?
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION diagnostic procedure. PCM Intermittent Condition Test.
2. VISUAL INSPECTION
NOTE: Anything that affects the speed of the crankshaft can cause a misfire DTC.
NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinder's Injector Control circuit.
NOTE: Misfires detected during a deceleration are indicators of mechanical concerns.
1. Visually inspect the engine for any of the following conditions:
- Worn serpentine belt. Testing and Inspection.
- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.
- Misalignment of the Water pump, P/S Pump and A/C Compressor pulleys.
- Corroded PCM power and ground circuits.
- Improper CKP, CMP, MAP and TPS mounting.
- Poor connector/terminal to component connection for CKP Sensor, CMP Sensor, MAP Sensor, TPS, Fuel Injector, Ignition Coil, etc.
- Vacuum leaks.
- Restricted Exhaust system. Perform the CHECKING EXHAUST RESTRICTION diagnostic procedure. Restriction Check.
- Restricted Air Induction system.
- Internal engine component failures.
- Overfilled engine oil or transmission.
- Extremely out of balance tires or warped brake rotors.
Were any of the above conditions present?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 3
3. CHECK FOR A FUEL OR IGNITION SYSTEM PROBLEM
1. Start the engine and allow it to idle long enough for the O2 Sensor to warm up and go into closed loop operation. This may take a couple of minutes.
2. With the scan tool, observe the voltage reading of the Downstream O2 Sensor for the bank on which the misfire was present.
NOTE:
If the misfire is caused by a lack of fuel condition, the O2 Sensor voltage will tend to stay at the low end of the range (approximately 2.5 volts). If the misfire is caused by a lack of or poor quality spark condition, the O2 Sensor voltage will tend to stay at the high end of the voltage range (approximately 3.5 volts).
Does the Downstream O2 Sensor voltage reading tend to be staying at the low end (2.5 volts) or high end (3.5 volts) of the voltage range.
High end of the range (3.5 volts)
- Go To 4
Low end of the range (2.5 volts)
- Go To 7
4. IGNITION SYSTEM OPERATION
WARNING:
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
1. Turn the ignition off.
2. Remove the Ignition Coils. .
3. Connect the Ignition Coil harness connectors.
4. Disconnect the Fuel Injector harness connector of the cylinder being tested.
5. Install a spark tester on the Ignition Coil.
6. While cranking the engine observe the spark coming from the spark tester.
NOTE:
Check all of the cylinders that were showing a misfire.
NOTE: A crisp blue spark that is able to jump the gap of the spark tester should be generated at the coil on plug and at the end of the ignition wire.
Is good spark present on all cylinders?
Yes
- Go To 5
No
- Go To 11
NOTE: Connect the Fuel Injector harness connector before continuing.
5. INSPECT THE SPARK PLUG
1. Turn the ignition off.
2. Remove the Spark Plug(s). .
3. Inspect the Spark Plug(s) for the following conditions:
- Cracks
- Carbon Tracking
- Foreign Material
- Gap size out of specifications
- Loose or broken electrode
NOTE: Lightly tap the bottom of the spark plug on a solid surface. The electrode in the spark plug should not move.
Were any of the above conditions present?
Yes
- Replace the Spark Plug. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 6
6. SPARK PLUG
1. Turn the ignition off.
2. Exchange the Spark Plug with a known good cylinder that was not indicating a misfire.
3. Start the engine and monitor the misfire monitor screen.
Did the misfire switch to the previously good cylinder?
Yes
- Replace the Spark Plug. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 7
7. FUEL PRESSURE CHECK
1. Perform the CHECKING THE FUEL DELIVERY SYSTEM test procedure. Testing and Inspection.
NOTE: Fuel pressure specification is 400 kPa +/- 14 kPa (58 psi +/- 2 psi).
Were any problems found with the fuel system?
Yes
- Perform the appropriate repairs.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 8
8. FUEL INJECTOR CONTROL
1. Turn the ignition off.
2. Disconnect the Fuel Injector harness connector of the misfiring cylinder.
3. Ignition on, engine not running.
NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinder's Injector Control circuit.
4. Install an Injector Noid light.
5. With the scan tool, actuate the Fuel Injector.
Does the Noid light blink/flicker during the actuation?
Yes
- Verify that there is good pin to terminal contact in the related Injector and the Powertrain Control Module connectors. Replace the Fuel Injector. Fuel Injector - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 9
9. INJECTOR CONTROL CIRCUIT
1. Turn the ignition off.
2. Remove the Injector Noid light.
3. Disconnect the PCM C2 harness connectors.
4. Check the Injector Control circuit for an open, short to ground and short to voltage.
Was a problem found with the Injector Control circuit?
Yes
- Repair the excessive resistance or short in the Injector Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 10
10. ENGINE MECHANICAL
1. Check for any of the following conditions/mechanical problems:
- ENGINE VACUUM - must be at least 13 inches in neutral
- ENGINE VALVE TIMING - must be within specifications
- ENGINE COMPRESSION - must be within specifications
- CYLINDER LEAKAGE TEST - must be within specifications
- ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks
- ENGINE PCV SYSTEM - must flow freely
- TORQUE CONVERTER STALL SPEED - must be within specifications
- POWER BRAKE BOOSTER - no internal vacuum leaks
- FUEL - must be free of contamination
- VALVE SPRINGS - cannot be weak or broken
- CAM LOBES - must not be worn excessively
- CAM SHAFTS - must not be worn or have excessive endplay
Are there any engine mechanical problems?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 15
11. CHECK THE (F343) ASD RELAY OUTPUT CIRCUIT
NOTE: The following test steps will apply to the suspect cylinder from step 4.
1. Turn the ignition off.
2. Disconnect the Coil on Plug harness connector.
3. Ignition on, engine not running.
4. With a scan tool, actuate the ASD Relay.
5. Using a 12-Volt test light connected to ground, probe the (F343) ASD Relay Output circuit in the Coil on Plug harness connector.
Does the test light illuminate brightly?
Yes
- Go To 12
No
- Repair the open or short to ground in the (F343) ASD Relay Output circuit between the PDC and Coil on Plug harness connector.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
NOTE: Stop All Actuations.
12. IGNITION COIL
WARNING:
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
1. Using a 12-Volt test light connected to a 12 volt source, probe the Coil Control circuit.
2. Crank the engine for 5.0 seconds while observing the test light.
What is the condition of the test light while cranking the engine?
Brightly blinking.
- Replace the Ignition Coil.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
ON constantly.
- Go To 13
OFF constantly.
- Go To 14
13. COIL CONTROL CIRCUIT SHORTED TO GROUND
1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Measure the resistance between ground and the Coil Control circuit in the Coil on Plug harness connector.
Is the resistance above 10k Ohms?
Yes
- Go To 15
No
- Repair the short to ground in the Coil Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
14. CHECK THE COIL CONTROL CIRCUIT FOR AN OPEN
1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Measure the resistance of the Coil Control circuit between the Coil on Plug harness connector and the PCM C2 harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 15
No
- Repair the open in the Coil Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
15. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Ignition Coil and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the Ignition Coil and the Powertrain Control Module connectors.
4. Search for any Technical Service Bulletins that may apply.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Replace and program the Powertrain Control Module.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.