Once engine misfire has been detected
and the fault codes downloaded from
the ECM, it is necessary to follow a
diagnostic path to correct the problem.
The ignition subset of the diagnostic
path is shown in
Table d. Ignition
system problems
Table c. Misfire fault codes
P code
BMW
fault
code
Fault code
Possible cause(s)
P0301
238
Misfire cylinder 1
Ignition fault: Defective or incorrect spark plug(s)
or connector(s); defective ignition coil(s)
Mechanical fault: Crankshaft pulse wheel loose
or damaged; damaged piston(s), valve(s) or
camshaft(s); oil pressure low
Catalyst fault: Excessive exhaust backpressure
due to restricted catalyst
Fuel supply fault: Contaminated fuel; fuel
delivery fault (blocked filter, low fuel in tank,
defective fuel pump); running loss system fault;
leaking or blocked fuel injector(s); fuel pressure
regulator fault; evaporative system fault
ECM/sensor input fault: Implausible sensor
signal; oxygen sensor(s) faulty; ECM faulty
P0302
239
Misfire cylinder 2
P0303
240
Misfire cylinder 3
P0304
241
Misfire cylinder 4
P0305
242
Misfire cylinder 5
P0306
243
Misfire cylinder 6
P1396
244
Crankshaft sensor
adaptation at limit
Misfire detection fault: Varying pulse wheel
tolerances or loose pulse wheel
Table d. Ignition system problems
Component
Condition
Test
Repair
Spark plug
Incorrect spark plug
Electrode gap too
small
Electrode(s) missing
Oil or fuel fouled
spark plug
Ceramic insulation
cracked
Inspect spark plugs.
Verify correct spark
plugs.
Replace plugs if
defective.
Check crankcase
ventilation and oil
level.
Ignition System
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