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Random Misfire Detected
DTC
P0300
Random Misfire Detected
DESCRIPTION
With the ignition switch ON or START, voltage is applied to the ignition coil. High
tension leads go to each cylinder from the ignition coil. The ignition coil fires two spark
plugs every power stroke (the cylinder under compression and the cylinder on the
exhaust stroke). Coil number one fires cylinders 1 and 4. Coil number two fires cylinders
2 and 5. And coil number three fires cylinders 3 and 6.
The ignition power transistor, controlled by the ECU, provides a switching circuit to
ground for energizing the primary ignition coils. When a primary ignition coil is energized
and deenergized, the secondary coil produces a high voltage spike across the attached
spark plugs. At the same time, the tachometer interface (part of the ignition power
transistor) provides the ECU and Transaxle Control Module (TCM) with an RPM signal.
TROUBLESHOOTING GUIDE
DTC detection condition
Background
a. If a misfire occurs while the engine is running, the
engine speed suddenly changes.
b. ECU checks for changes in the engine speed by
monitoring the CKP signal.
Normal Operation
a. Five seconds or more have passed after the engine
has started.
b. The engine speed is between 500 and 6,000 r/min.
c. The engine Coolant Temperature is higher than -
10°C(14°F).
d. The intake air temperature is higher than -10°C
(14°F).
e. There is no sudden acceleration/deceleration such
as during a shift change.
Abnormal Operation (a change in the rate of angular
acceleration by the crankshaft is monitored for misfire
detection.)
Diagnostic item
a. Failed ignition system
part(s)
b. Poor crankshaft position
sensor signal
c. Incorrect air/fuel ratio
d. Low compression
e. Failed WTS
f. Timing belt missing teeth
g. Failed injector
h. Failed ECU
Probable cause
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