P0301,P0302, P0303, P0304
Symptom: The CHECK ENGINE lamp (MIL) is on or flashing. Uneven running when
misfiring. Any other diagnostic trouble codes.
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P0301
,
P0302
,
P0303
,
P0304
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Misfiring, cylinders 1, 2, 3, 4
Fault symptoms
The CHECK ENGINE lamp (MIL) is on or flashing. Uneven running when
misfiring. Any other diagnostic trouble codes.
Conditions
During the course of each cylinder's power stroke the rotational speed of the
crankshaft increases temporarily. This gives rise to momentary increases in pulse frequency
from the crankshaft position sensor. These frequency changes are evaluated by the control
module and any misfiring is recorded.
An engine load and speed dependent matrix in the electronic control module's
memory determines how large a proportion of misfires is required for exhaust emissions to
reach prohibited limits or for the three way catalytic converter to be damaged.
A diagnostic trouble code will be generated if the number of misfires exceeds the matrix
figure.
Diagnostic help
The cause of misfiring could be:
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defective or incorrect spark plugs
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Check the wiring
Intermittent faults may occur as a result of temporary short circuits and breaks in the
wiring. Jiggle the wiring at several points and in different directions to ascertain whether the
wiring harness, including any connectors, is causing the trouble. Observe the multimeter,
ISAT scan tool or test lamp while doing this.
Diagnostic procedure
1. Check other Motronic 4.1 diagnostic trouble codes
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Use an ISAT scan tool to obtain
readouts of all diagnostic trouble codes.
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Does the ISAT scan tool show diagnostic trouble codes P1213-P1216, P1225-
P1228?
Continue fault diagnosis for the relevant diagnostic trouble code.
Continue with point 2.
2. Check the spark plugs
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Remove the spark plug from the
cylinder concerned and check its condition visually.
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Check that the electrode gap is not
wider than 1.0 mm and that the spark plug is not obviously damaged.
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Is the plug OK?
Continue with point 3.
Change all spark plugs. Continue with point 7.
3. Check the ignition system
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Unplug the injector
connectors.
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Fit a test spark plug (part No. 86 11
386) in the relevant HT cable.
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Check that the test spark plug produces a spark.
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Is a spark produced?
Change all spark plugs. Continue with point 5.
Continue with point 4.
4. Check the HT cables
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Try changing the relevant HT cable
for a new one.
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Fit a test spark plug to the relevant
HT lead.
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Check that a spark is
produced.
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Is a spark produced?
Changing the HT cable was the correct procedure to rectify the fault. Continue
with point 7.
The fault is to be found in the distributor. Rectify the fault and proceed to point
7.
5. Check the compression
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Carry out a compression test on
the relevant cylinder.
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Is the compression OK?
Continue with point 6.
Continue fault diagnosis as described in Basic engine
.
6. Check the fuel flow capacity of the relevant
injector
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Check the fuel delivery flow of the
relevant injector.
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Is the flow capacity OK?
Continue with point 7.
Change the injector. Continue with point 7.
7. Final check
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Clear the diagnostic trouble code.
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Implementation of driving cycle:
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Evaluation of driving cycle:
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Does misfiring occur?
Continue as described in
.
The steps taken to rectify the fault were
correct.
