P0301
MISFIRING IN CYLINDER 1, 2, 3 OR 4
Symptom Of Fault.
The CHECK ENGINE lamp (MIL) is on or flashing. Uneven running when misfiring. Possibly other diagnostic trouble codes.
Conditions.
An engine load and speed dependent matrix in the engine control module's memory specifies 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. If the number of misfires exceeds the matrix value, a diagnostic trouble code will be generated.
If misfiring occurs in more than one cylinder, the cylinder in question accounts for more than 95% of the misfires.
Diagnostic.
The injectors and the corresponding ignition coils can be activated using an ISAT scan tool.
- Select "ACTIVATE".
- Select "INJECTORS" and "IGNITION COILS".
Then select the cylinder concerned in the appropriate submenu.
Momentary misfiring can be ascertained using an ISAT scan tool.
- Select "READ FUNCTIONS".
- Select "MISFIRING CYLINDER 1
Other cylinders can also be selected.
Checking The Wiring.
Intermittent faults may occur as a result of occasional short circuits and breaks in the wiring. Jiggle the leads and in-line connectors at several places and in different directions to reveal faults in the wiring harness. Observe the multimeter, ISAT scan tool or test lamp while carrying out, this check.
Diagnostic Procedure.
1. Check the operation of the ignition coil concerned
- Connect an ISAT scan tool.
- Ignition switch in ON position.
- Select "ACTIVATE".
- Select "IGNITION COILS"
- Select "IGNITION CYL I", "CYL 2", "CYL 3" or "CYL 4".
- Select the cylinder concerned. Activation of an ignition coil takes place for 10 seconds at 200 Hz. If a longer activation time is required, the command must be repeated.
- Listen for the sound of each ignition coil operating.
Is the ignition coil In question operating?
YES: Proceed to point 4.
NO: Continue with point 2.
2. Check the trigger lead of the ignition coil concerned
- Unplug the ignition discharge module's 10-pin connector.
- Ignition switch in ON position.
The test lamp must light up with extremely short interruptions for 10 seconds. In the event of uncertainty, repeat the command.
Does the test lamp light up and start flickering?
YES: Change the ignition discharge module and proceed to point 12.
NO: The test lamp does not light up or remains on continuously- Continue with point 3.
- Connect the test lamp to pin 10 and the trigger lead of the ignition coil in question, see table below.
- Then activate the ignition coil concerned by means of an ISAT scan tool command.
3. Check the trigger lead in question
- Check the trigger lead in question for continuity, see table.
- Check the lead for continuity/shorting.
Is the lead OK?
YES: Continue with point 4.
NO: Rectify the fault and proceed to point 12.
4. Check the condition of the ignition discharge module. Remove the ignition discharge module from the camshaft cover.
Check Visually:
^ that the four rubber seals for the. spark plugs are in good condition.
^ that no contact spring for the spark plugs is missing or that spring travel is inadequate. the connector for moisture and corrosion.
Is the ignition discharge module OK?
YES: Continue with point 5.
NO: Rectify the fault and proceed to point 5.
5. Check the spark plugs
- Remove the spark plugs and check their condition visually.
Are the plugs OK?
YES: Continue with point 6.
NO: The electrode gap is wider than 1.4 mm or is otherwise obviously incorrect. Change the spark plugs and proceed to point 12.
WARNING: The electronic ignition system generates up to 40,000 Volts. Such Voltages can prove fatal to people with weak hearts are fitted with pacemaker. All due caution should therefore be observed when carrying out any work involving the ignition system.
IMPORTANT: The ignition discharge module must be positioned with the ignition coils downwards during the test so that the transformer oil will provide good insulation in the high-tension part of the coils.
6. Check the operation of the ignition discharge module-
- Install a test spark plug (part No. 86 11 386) in the relevant spark plug socket.
- Ground the plug using test cable 86 10 867.
- Ignition switch in ON position.
- Activate the ignition coil concerned, using the ISAT scan tool.
- Check that the activated spark plug produces a spark.
Is a spark produced?
YES: continue with point 7.
NO: Change the ignition discharge module and proceed to point 12.
7. Check the compression
- Check the compression of each cylinder.
Is compression OK?
YES: Change all spark plugs and continue with point 8.
NO: Continue fault diagnosis in the Basic Engine.
8. Check the power supply (B+) of the injector concerned
- Check the voltage by connecting the test lamp to pin 1 of the relevant injector's connector and B -.
- Connect an ISAT scan tool.
- Select "ACTIVATE".
- Select "INJECTOR CYL 1", "CYL 2", "CYL 3" or "CYL 4".
The test lamp should light up for 10 seconds during activation.
Is the test lamp on?
YES: Continue with point 9.
NO: The fault is in the lead between pin 1 and crimped connection J67. Rectify the fault and proceed to point 12.
9. Check the relevant injector's engine control module output
- Unplug the relevant injector's connector.
- Connect the test lamp to pins 1 and 2 of the injector's connector.
- Ignition switch in the ON position.
- Activate the relevant injector using the. ISAT scan tool and the command "INJECTOR "CYL1", "CYL 2", "CYL 3" or "CYL 4".
The test lamp must flash at a frequency of 10 Hz for 10 seconds. Repeat the command in the event of uncertainty.
Does the test lamp flash?
YES: Continue with point 10.
NO: The test lamp flashes or remains on continuously. Check and, if necessary, rectify the lead between pin 2 and the relevant engine control module output.
If the lead is OK, proceed to point 12.
10. Check the resistance of the relevant injector
- Take a resistance reading across pins 1 and 2 of the relevant injector's connector. Nominal resistance is: 12 ± 0.35 ohms at 20° C (68 °F).
Is the resistance reading OK?
YES: Continue with point 11.
NO: Change the injector and proceed to point 12.
11. Check the relevant injector's fuel delivery flow
- Measure the delivery flow.
Is the delivery flow OK?
YES: Continue with point 12.
NO: Change the injector and proceed to point 12.
12. Final check:
- Clear the diagnostic trouble code.
- Implementation of driving cycle: Drive the car at different engine rpm and varying loads, especially at high revs, while the engine is warming up.
- Evaluation of driving cycle: Check whether the diagnostic trouble code has recurred.
Has the diagnostic trouble code recurred?
YES: Continue at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO: The remedial measure taken was correct.