Trouble Code: P0302 (4.2L L6 VIN S
Auto)
Cylinder 2 Misfire Detected
Print this code data
Number of Trips to Set Code: 2
OBD II Monitor Type: CCM Details
Indicators: MIL Details
 MISFIRE Details
 MIL Details
Trouble Code Conditions:
DTC P0013, P0014, P0105, P0107, P0112, P0113, P0117, P0118, P0122,
P0123, P0125, P0128, P0130-P0140, P0171-P0172, P0325, P0336,
P0502-P0503, P0506-P0507, P0601, P0602, P1133, P1137, P1138,
P1171, 1336 and P1621 not set, engine speed from 469-5900 rpm, DFCO
and EGR Test off, system voltage over 10.0v, ECT sensor from 20-254ºF,
TP angle stable and the PCM detected a crankshaft speed variation
characteristic of a misfire in Cylinder 2. Note: If the misfire is severe, the
MIL will flash on/off on one trip!
Possible Causes:

Air leak in the intake manifold, or in the EGR or
PCV system
 Base engine mechanical fault that affects only
Cylinder 2
 Fuel delivery component fault that affects only
Cylinder 2 (i.e., a contaminated, dirty or sticking fuel
injector)
 Ignition system problem (coil or plug) that affects
Cylinder 2
 TSB 87-65-08 contains a repair procedure for this
code
2002 Chevrolet Trailblazer - Powertrain - Engine Controls - 4.2L DTC P0301-P0306
PATH: Diagnostics > Diagnostic Routines > Powertrain > Engine Controls 4.2L > DTC P0301-P0306
DTC P0301-P0306
NOTE
Applicable vehicles:
 Bravada, Envoy, TrailBlazer (VIN S/T)
DTC P0301-P0306
Circuit Description
The powertrain control module (PCM) uses information from the
crankshaft position (CKP) sensor and the camshaft position (CMP) sensor
in order to determine when an engine misfire is occurring. By monitoring
variations in the crankshaft rotation speed for each cylinder, the PCM is
able to detect individual misfire events. DTCs P0301 through P0306
correspond to cylinders 1 through 6. If the PCM is able to determine that a
specific cylinder is misfiring, the diagnostic trouble code (DTC) for that
cylinder will set. If the misfire is random and on multiple cylinders, DTC
P0300 will set. A misfire rate that is high enough can cause three-way
catalytic converter damage. The malfunction indicator lamp (MIL) will
flash ON and OFF when the conditions for catalytic converter damage are
present.
Conditions for Running the DTC
 DTCs P0013, P0014, P0105, P0107, P0108, P0117,
P0118, P0122, P0123, P0125, P0128, P0217, P0218,
P0336, P0340, P0341, P0365, P0366, P0502, P0503,
P1114, P1115, P1121, P1122, P1336, and P1345 are
not set.
 The engine is running.
 The system voltage is 10-18 volts.
 The engine coolant temperature (ECT) is 7-130°C
(19-266°F).
 The throttle angle is steady.
 The A/C compressor clutch is not changing state.
 The exhaust gas recirculation (EGR) flow test is
inactive.
 The fuel level is above 10 percent.
 The fuel cut-off or decel fuel cut-off (DFCO) mode
is not active.
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

If the misfire level is non-catalyst damaging, the
PCM will illuminate the MIL during the second key
cycle in which the DTC sets.
 If the misfire is severe enough to cause possible
catalyst damage, the PCM will immediately flash the
MIL while the misfire remains at catalyst damaging
levels.
 The PCM will disable the torque converter clutch
(TCC) operation.
 The PCM will store the conditions present when the
DTC set as Freeze Frame/Failure Records data.
 Any data previously stored in Freeze Frame will be
overwritten when this DTC sets. The only exception
to this is if a fuel trim DTC was already recorded in
Freeze Frame. In this case, the fuel trim data stays in
Freeze Frame and the Misfire Data will be stored in
Failure Records.
Conditions for Clearing the MIL/DTC
 The PCM will turn the MIL OFF after three
consecutive trips during which the diagnostic runs
and passes.
 Note that if the last failure was during a non-typical
driving condition, the MIL may remain ON longer
than three drive trips. Review Freeze Frame for the
last failure conditions.
 The History DTC will clear after 40 consecutive
warm-up cycles have occurred without a
malfunction.
 The DTC can be cleared by using the scan tool Clear
DTC Information function.
Diagnostic Aids
Check for the following conditions:
 Incorrect CKP system variation data stored in the
PCM--Run the Crankshaft Position System
Variation Learn using the scan tool.
 System grounds--Ensure that all connections are
clean and properly tightened.
 Damaged accessory drive belt or driven accessory--A
damaged serpentine belt or belt driven accessory can
cause engine load variations sufficient to set a
misfire DTC.
 Fuel pressure--Perform a fuel system pressure test. A
malfunctioning fuel pump, plugged filter, or




malfunctioning fuel system pressure regulator will
contribute to a lean condition. Refer to Fuel System
Diagnosis .
Fuel injectors--Refer to Fuel Injector Solenoid Coil
Test .
Contaminated fuel--Refer to Alcohol/Contaminantsin-Fuel Diagnosis .
Extended idle--Excessive Open Loop operation
caused by extended idling or short trip driving may
leave deposits on the heated oxygen sensors (HO2S).
The deposits cause oxygen sensors to respond slowly
to exhaust oxygen content, affecting fuel control and
causing a misfire to be indicated at idle. This
condition is not permanent. To determine if this
condition is causing the DTC P0300 to be set, review
the Freeze Frame/Failure Records data for DTC
P0300. If the DTC P0300 occurs at high engine
speeds, the condition described above did not cause
the DTC P0300 to set. If the DTC P0300 occurs at
idle or very low engine speeds and at engine coolant
temperatures below 80°C (176°F), the condition
described above is very likely the cause of the DTC
P0300 being set. The deposits on the heated oxygen
sensors can be eliminated by operating the vehicle
fully warm at mass air flows above 15 g/s.
Running the vehicle low on fuel--This DTC may set
if the vehicle misfires while running out of fuel. If no
misfire is currently present, but the History Counters
indicate random misfire was once present, ask if the
vehicle has been run out of fuel. If this is the case, no
further repair may be necessary.
WARNING
Important: If the level of misfire was sufficient to cause possible catalyst
damage (if the MIL was flashing), ensure that the DTC P0420 test is
completed and passed after verifying the misfire repair.
If the condition is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. DTCs that may cause a misfire DTC to set may include
those for injector control circuits, oxygen sensors, the
evaporative emission (EVAP) system, or fuel trim.
7. This test is to determine if there is a problem in the heated
oxygen sensor (HO2S) or wiring that is causing the PCM
to alter the fuel trim. When the sensors are disconnected,
the fuel system should go into Open Loop. If the misfire
counters stop incrementing, perform the HO2S diagnosis
for sensor 1.
Step
Action
Did you perform the Diagnostic System CheckEngine Controls?
Yes
1
Go to Step 2
2
3
4
Check for other DTCs that may cause
a misfire.
Did you find any other DTCs?
No
Go to
Diagnostic
System
Check Engine
Controls
Go to
Diagnostic
Trouble
Code (DTC)
Go to Step 3
List
1. Connect the scan tool.
2. Start the engine.
3. Allow the engine to idle
or operate within the
conditions listed in the
Freeze Frame records.
4. Using the scan tool,
monitor the Misfire
Current Counter for
this cylinder.
Is the Misfire Current Counter
incrementing?
Go to Step 4
Go to
Diagnostic
Aids
Inspect the following items:
 The vacuum
hoses for splits,
kinks and proper
connections
 The throttle body
and the intake
manifold for
Go to Step 8
Go to Step 5
Step
5
6
7
Action
vacuum leaks
 The crankcase
ventilation valve
and/or system
for vacuum leaks
 Ensure that the
PCM grounds
are clean and
secure.
Did you find and correct the
condition?
Yes
No
1. Perform the Fuel
Injector Balance Test
with Tech 2 and the
Fuel Injector
Solenoid Coil Test on
the affected cylinder.
2. Repair as necessary.
Did you find and correct the
condition?
Go to Step 8
Go to Step 6
1. Perform the Ignition
System Check on the
affected cylinder.
Refer to Electronic
Ignition (EI) System
Diagnosis .
2. Repair as necessary.
Did you find and correct the
condition?
Go to Step 8
Go to Step 7
1. Turn OFF the ignition.
2. Disconnect the HO2S 1
connector.
3. Start the engine and
allow the engine to
idle.
4. Using the scan tool,
monitor the Misfire
Current Counter for
this cylinder.
Is the Misfire Current Counter
Go to
Symptoms Engine
Mechanical in
Engine
Go to DTC
Mechanical
P0130
Step
Action
Yes
No
1. Use a scan tool to clear
the DTCs.
2. Turn OFF the ignition
for 30 seconds.
3. Start the engine.
4. Operate the vehicle
within the Conditions
for Running the DTC
as specified in the
supporting text.
Does the DTC run and pass?
Go to Step 9
Go to Step 2
Go to
Diagnostic
Trouble
Code (DTC)
List
System OK
incrementing?
8
9
With a scan tool, observe the stored
information, Capture Info.
Does the scan tool display any DTCs
that you have not diagnosed?