DTC P0300 Engine Misfire Detected
Circuit
Description
The Crankshaft Position
sensor is mounted through the side of the engine block at the rear of Bank 2
behind the starter assembly. The Crankshaft Position sensor works in
conjunction with a 24X reluctor wheel on the crankshaft. The reluctor wheel is
inside the engine immediately in front of the rear main bearing. The PCM
provides a 12 volt power supply to the CKP sensor as well as a ground and a
signal circuit.
A misfire causes a
change in crankshaft speed. The PCM times the interval between each pulse and
compares each new time interval with the previous one in order to determine
when an excessive change in crankshaft speed has occurred. You can expect a
certain amount of acceleration/deceleration between each firing stroke, but if
the crankshaft speed changes are greater than an expected amount, the PCM
interprets this as a misfire.
The PCM uses the
Crankshaft Position sensor for both spark and fueling. As the crankshaft
rotates, the reluctor wheel teeth interrupt a magnetic field produced by a magnet
within the sensor. The sensors internal circuitry detects this and produces a
signal which the PCM reads. The PCM uses this 24X signal in combination with
the Camshaft Position sensor 1X signal in order to accurately determine
crankshaft position. The PCM also calculates a 4X signal from this information.
The PCM uses the 4X signal for internal calculations. The 4X signal also
provides a tach signal for any device which requires one.
Observe that as long as
the Crankshaft Position sensor 24X signal is available, the engine will start.
The PCM can determine top dead center for all cylinders by using the Crankshaft
Position sensor 24X signal alone. The Camshaft Position sensor 1X signal is
used by the PCM to determine if the cylinder at top dead center is on the
firing stroke, or the exhaust stroke. The system attempts synchronization and
looks for an increase in engine speed indicating the engine started. If the PCM
does not detect an increase in engine speed, the PCM incorrectly synchronized
to the exhaust stroke and will re-sync to the opposite cam position. A slightly
longer cranking time may be a symptom of this condition.
Conditions
for Running the DTC
- DTCs P0101, P0102, P0103, P0107,
P0108, P0117, P0118, P0121, P0122, P0123, P0125, P0335, P0336, P0341,
P0342, P0343, P0500, P0502, P0503, P1258 not set.
- The engine speed is between 450 RPM
and 3,001 RPM.
- The ignition voltage is between 11.0
volts and 16 .0 volts.
- The engine coolant temperature is
between -7°C (19°F) and 130°C (266°F).
- Fuel level greater than 10%
- The TP sensor angle is steady within
1%.
- The ABS and Traction Control systems
are not active.
- The transmission is not changing
gears.
- The AIR diagnostic test is not in
progress
- The A/C clutch is not changing
states.
- The PCM is not in fuel shut-off or
decel fuel cut-off mode.
- The ABS signals not exceeding rough
road thresholds.
Conditions
for Setting the DTC
- The PCM determines that an emission
type Misfire is present.
- The PCM determines that a catalyst
damaging Misfire is present.
Action
Taken When the DTC Sets
The PCM will illuminate
the Malfunction Indicator Lamp (MIL) under the following conditions:
- The PCM illuminate the Malfunction
Indicator Lamp (MIL) on the second consecutive ignition cycle that the
diagnostic runs and fails, if the diagnostic fails under the same
conditions (load, RPM, temperature, etc.) as the previous ignition cycle
that the test ran and failed.
- The first time the diagnostic fails,
the PCM records the operating conditions in Failure Records.
- The second consecutive ignition
cycle that this diagnostic fails [under the same conditions (load, RPM,
temperature, etc.) as the previous ignition cycle that the test ran and
failed], the PCM stores this information in Freeze Frame. The PCM copies
any data previously stored in Freeze Frame and copies the data into the
Failure Records. The PCM then overwrites the Freeze Frame. The only
exception to this is if a Misfire DTC was already recorded in Freeze
Frame. In this case, the Misfire data stays in Freeze Frame and the PCM
updates the Fuel Trim data in the Failure Records.
- The PCM determines the percent of
misfire over a 1,000 revolution period is high enough to cause excessive
tail pipe emissions. The PCM illuminates the Malfunction Indicator lamp
the next consecutive ignition cycle that the diagnostic runs and fails, if
the diagnostic fails under the same conditions (load, RPM, temperature,
etc.) as the previous ignition cycle that the test ran and failed.
Conditions
for Clearing the MIL/DTC
Important
If the last failure was
during a non-typical driving condition, the MIL may remain ON longer than the
three ignition cycles. Review the Freeze Frame/Failure Records for the last
failure conditions.
- The PCM turns the MIL OFF after
three consecutive ignition cycles that the diagnostic runs and does not
fail within the same conditions that the DTC last failed.
- A History DTC clears after forty
consecutive warm-up cycles, if this or any other emission related
diagnostic does not report any failures.
- A last test failed (Current DTC)
clears when the diagnostic runs and does not fail.
- Use a scan tool in order to clear
the MIL/DTC.
Diagnostic
Aids
Important
- Remove any debris from the PCM connector surfaces
before servicing the PCM. Inspect the PCM connector gaskets when
diagnosing/replacing the PCM. Ensure that the gaskets are installed
correctly. The gaskets prevent contaminate intrusion into the PCM.
- For any test that requires probing the PCM or a
component harness connector, use the Connector Test Adapter Kit J 35616-A .
Using this kit prevents damage to the harness connector terminals.
- Running the vehicle out of fuel
causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel
may have DTC P0461 also set.
- A restricted fuel filter can cause
sufficient misfire to set DTC P0300. Refer to Fuel
System Diagnosis .
- Observe, if more than one cylinder
is mis-firing, the scan tool may only display one cylinder mis-firing.
This will not be apparent until the repair is complete.Also, if an
ignition coil/module ground circuit is open for one side of the engine,
the scan tool may only display 2 or 3 cylinders mis-firing. Inspect the
ground circuit for the ignition coil/modules on the cylinder bank of the
engine that has more than one cylinder mis-firing.
- Excessive vibration from sources
other than the engine could cause a misfire DTC. The following are
possible sources of vibration:
- Variable thickness brake rotor
- Drive shaft not balanced
- Certain rough road conditions
- Using the Freeze Frame and/or
Failure Records data may aid in locating an intermittent condition. If you
cannot duplicate the DTC, the information included in the Freeze Frame
and/or Failure Records data can help determine how many miles since the
DTC set. The Fail Counter and Pass Counter can also help determine how
many ignition cycles the diagnostic reported a pass and/or a fail. Operate
the vehicle within the same freeze frame conditions (RPM, load, vehicle
speed, temperature etc.) that you observed. This will isolate when the DTC
failed.
- For an intermittent condition, refer
to Symptoms
.
Test
Description
The numbers below refer
to the step numbers on the diagnostic table.
- The misfire current
counters will not increment when engine load is low.
Wetting down the secondary ignition system
with water from a spray bottle may help locate damaged or deteriorated
components. Look/listen for arcing or misfiring as you apply the water.
If the Misfire Cur counters are
incrementing and there is no apparent misfire, an erratic CKP sensor signal
could be the cause. Perform the diagnostic table for DTC P0335 first if this
condition is suspected.
If a misfire is present and you suspect a
fuel control condition, force the fuel system into Open Loop using the scan
tool and allow the engine to run for a few minutes. If this eliminates the
misfire, refer to any fuel control related DTCs which are set. If no other DTCs
are set, refer to the Engine Scan Tool Data List.
- The cylinder with
the more significant misfire may cause another cylinders counter to
increment only by a small amount.
- If the engine
misfire moves with the spark plug, this is good indication that you should
replace the spark plug.
- If you cannot find
any fuel system conditions, refer to Engine Mechanical. An engine
mechanical condition can cause a spark plug to foul. Inspect the engine
for loose rockers, collapsed lifters or worn camshaft lobes.
- If the customers
concern is the MIL is flashing, this indicates that a Catalyst Misfire has
occurred. Drive the vehicle in the conditions to run the catalyst
diagnostic. Refer to DTC
P0420 Catalyst System Low Efficiency Bank 1 and/or DTC
P0430 Catalyst System Low Efficiency Bank 2 .
|
DTC P0300 - Engine Misfire Detected
Step
|
Action
|
Value(s)
|
Yes
|
No
|
|
1
|
Did
you perform the Powertrain On-Board Diagnostic (OBD) System Check?
|
--
|
Go
to Step 2
|
Go to A
Powertrain On Board Diagnostic (OBD) System Check
|
|
2
|
Important
Automatic Transmission
- Install the scan tool.
- Idle the engine.
- Turn all the accessories ON (i.e.
lights, A/C, rear defogger).
- Set the Park Brake.
- Transmission in drive.
- Monitor all of the Misfire Cur.
counters on the misfire data list (one counter per cylinder) using the
scan tool.
Manual Transmission
- Install the scan tool.
- Idle the engine.
- Turn all the accessories ON (i.e.
lights, A/C, rear defogger).
- Set the Park Brake.
- Transmission in neutral.
- Select the special functions and
RPM control using the scan tool.
- Lower the engine speed to the
specified value.
- Select the misfire data list while
in the RPM control portion of the scan tool. You can select the misfire
list by pressing the More and then the Next List/Previous list soft key
on the scan tool. The Soft Key will have to be selected a few times to
reach the misfire data list.
- Monitor all of the Misfire Cur.
counters on the misfire data list (one counter per cylinder) using the
scan tool.
Are
any of the Misfire Cur. counters incrementing?
|
--
|
Go
to Step 4
|
Go
to Step 3
|
|
3
|
- Turn ON the ignition leaving the
engine OFF.
- Review the Freeze Frame and/or
Failure Records data for this DTC and observe the parameters.
- Turn OFF the ignition for 15 seconds.
- Start the engine.
- Operate the vehicle within the
conditions required for this diagnostic to run, and as close to the
conditions recorded in Freeze Frame/Failure Records as possible. Special
operating conditions that you need to meet before the PCM will run this
diagnostic, where applicable, are listed in Conditions for Running the
DTC.
- Select the Diagnostic Trouble Code
(DTC) option, the Specific DTC option, and then enter the DTC number
using the scan tool.
Does
the scan tool indicate that this diagnostic failed this ignition?
|
--
|
Go
to Step 4
|
Go to Diagnostic Aids
|
|
4
|
Is
only one Misfire counter incrementing?
|
--
|
Go
to Step 6
|
Go
to Step 5
|
|
5
|
Visually/physically
inspect the following items:
- Accessory drive belt and pulleys for
damage or misalignment. Refer to Drive
Belt Diagnosis in Engine Mechanical 5.7L.
- Vacuum hoses for splits, kinks and
proper connections.
- Throttle body and intake manifold
for vacuum leaks.
- Crankcase ventilation valve and/or
system for vacuum leaks.
- PCM grounds for being clean and
secure. Refer to Ground
Distribution Schematics in Wiring Systems.
- Verify that all injector harness
connectors are connected to the proper injector/cylinder.
- Inspect the injector and Ignition
Control fuses for being open. If you find an open fuse, locate and
repair the shorted circuit. Refer to Wiring
Repairs in Wiring Systems.
- Test for low fuel pressure or
restricted fuel flow. Refer to Fuel
System Diagnosis .
- Inspect for a restricted exhaust.
- Poor fuel quality. Refer to Alcohol/Contaminants-in-Fuel
Diagnosis .
Did
any of the above steps isolate a condition requiring a repair?
|
--
|
Go
to Step 17
|
Go
to Step 6
|
|
6
|
- Turn OFF the ignition.
- Disconnect the injector that
corresponds to the Misfire Cur counter(s) that was incrementing.
- Connect the injector test lamp J 34730-405
to the injector electrical connector.
- Idle the engine.
Is
the injector test lamp flashing?
|
--
|
Go
to Step 7
|
Go to Fuel
Injector Circuit Diagnosis
|
|
7
|
- Turn OFF the ignition.
- Reconnect the injector harness
electrical connector.
- Disconnect the ignition wire(s)
from the spark plug that corresponds to the Misfire Cur counter(s) that
was incrementing. Refer to Spark
Plug Wire Harness Replacement in Engine Electrical.
- Install spark tester J 26792
to a ground.
- Start and idle the engine.
Does
the spark jump the tester gap and is the spark consistent?
|
--
|
Go
to Step 9
|
Go
to Step 8
|
|
8
|
- Remove the ignition wire for the
cylinder that is Mis-firing.
- Measure the resistance of the
ignition wire using the DMM J 39200 .
Is
the ignition wire resistance less than the specified resistance?
|
700ohms
|
Go to Electronic
Ignition (EI) System Diagnosis
|
Go
to Step 16
|
|
9
|
- Remove the spark plug(s) from the
cylinder(s) that indicated a misfire. Refer to Spark
Plug Replacement in Engine Electrical.
- Visually inspect the spark plug(s)
for the affected cylinder(s).
Does
the spark plug appear to be OK?
|
--
|
Go
to Step 10
|
Go
to Step 11
|
|
10
|
- Exchange the suspected spark plug
with another cylinder that is operating properly.
- Operate the vehicle under the same
conditions that the misfire occurred.
Important
If the Injector Coil Test
Procedure fails to locate the cause of the fault, refer to Base
Engine Misfire Diagnosis in Engine Mechanical 5.7L.
Did
the misfire move with the spark plug?
|
--
|
Go
to Step 15
|
Go to Fuel
Injector Coil Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C
(50-95 Degrees F)
|
|
11
|
Are
the spark plugs oil or coolant fouled?
|
--
|
Go to Base
Engine Misfire Diagnosis in Engine Mechanical 5.7L.
|
Go
to Step 12
|
|
12
|
Important
If no concern can be
located with the fuel system, refer to Base
Engine Misfire Diagnosis in Engine Mechanical 5.7L.
Are
the spark plugs gas fouled?
|
--
|
Go to Fuel
System Diagnosis
|
Go
to Step 13
|
|
13
|
Important
If the Injector Coil Test
Procedure fails to locate the cause of the fault, refer to Base
Engine Misfire Diagnosis in Engine Mechanical 5.7L.
Do
the spark plugs show any signs of being cracked, worn, or improperly gapped?
|
--
|
Go
to Step 14
|
Go to Fuel
Injector Coil Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C
(50-95 Degrees F)
|
|
14
|
Replace
or re-gap spark plugs. If improper gap is found, be sure to re-gap spark
plugs using a wire type gauge, J 41319. Is the action complete?
|
--
|
Go
to Step 17
|
--
|
|
15
|
Replace
the faulty spark plug(s). Refer to Spark
Plug Replacement in Engine Electrical. Is the action complete?
|
--
|
Go
to Step 17
|
--
|
|
16
|
Replace
the faulty ignition wire(s). Refer to Spark
Plug Wire Harness Replacement in Engine Electrical. Is the action
complete?
|
--
|
Go
to Step 17
|
--
|
|
17
|
Was
the customers concern that the MIL was flashing?
|
--
|
Go to DTC
P0420 Catalyst System Low Efficiency Bank 1 or DTC
P0430 Catalyst System Low Efficiency Bank 2 .
|
Go
to Step 18
|
|
18
|
- Select the Diagnostic Trouble Code
(DTC) option and the Clear DTC Information option using the scan tool.
- Idle the engine at the normal
operating temperature.
- Select the Diagnostic Trouble Code
(DTC) option and the Specific DTC option, then enter the DTC number
using the scan tool.
- Operate the vehicle within the
Conditions for Running the DTC as specified in the supporting text, if
applicable.
Does
the scan tool indicate that this test ran and passed?
|
--
|
Go
to Step 19
|
Go
to Step 2
|
|
19
|
Select
the Capture Info option and the Review Info option using the scan tool. Does
the scan tool display any DTCs that you have not diagnosed?
|
--
|
Go to the applicable
DTC table
|
System OK
|