P0306
MISFIRING, CYLINDER 1,2,3,4,5 OR 6
Fault Symptoms
CHECK ENGINE lamp (MIL) on.
Lumpy running while 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.
How large a proportion of misfires is required for exhaust emissions to reach illegal levels or for the catalytic converter to be damaged is specified in a load and rpm dependent matrix in the control module's memory.
A diagnostic trouble code will be generated if the number of misfires exceeds the matrix figure.
Diagnostic Help.
The cause of the misfiring could be low fuel level in the tank. If this is the case, it will be indicated by diagnostic trouble code P1585 also being generated.
The injectors and ignition coils can be activated with the ISAT scan tool.
- Select "ACTIVATE".
- Select "INJECTOR 1" (2, 3, 4, 5 or 6) and "IGNITION CYL 1-4" (2-5 or 3-6).
The cause of the diagnostic trouble code could be:
^ a defective spark plug, HT cable or ignition coil
^ a defective/clogged injector
^ poor compression in basic engine
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 diagnostic trouble codes in the Motronic system
- Use an ISAT scan tool to obtain readouts of all diagnostic trouble codes.
Does the ISAT scan tool show any of the following diagnostic trouble codes?
^ P1585
^ P1213-P1230
^ P0300 together with at least 2 of the following diagnostic trouble codes: P0301, P0302, P0303, P0304, P0305, P0306. In such case, proceed with fault diagnosis as described for diagnostic trouble code P0300.
YES: Continue fault diagnosis according to the diagnostic procedure for the relevant diagnostic trouble code.
NO: Continue with point 2.
WARNING: The electronic ignition system generates charges of up to 40,000 volts. Such voltages may prove fatal to persons with a weak heart or those who are fitted with a pacemaker. Therefore, treat the ignition system with due respect and take all necessary precautions.
2. Check the performance of the ignition coil module
- Fit a test spark plug, part No. 86 11 386, in the relevant cylinder and use a "new" HT cable.
- Connect the spark plug to ground using test cable assembly 86 10 867.
- Turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "IGNITION CYL X-Y".
The command activates the ignition coil at a frequency of 0.5 Hz for 30 seconds.
- Check that the activated spark plug produces a spark.
Is a spark produced?
YES: Continue with point 3.
NO: Continue with point 4.
3. Check the relevant HT cable
- Fit a test spark plug, part No. 86 11386, in the relevant cylinder. Use the existing HT cable.
- Ground the plug using test cable 86 10 867.
- Turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "IGNITION CYL X-Y".
The command, activates the ignition coil at a frequency of 0.5 Hz for 30 seconds.
- Check that the activated spark plug produces a spark.
Test satisfactory?
YES: Continue with point 5.
NO: Change the relevant HT cable. Then continue with point 8.
4. Check the relevant control module output to the ignition coil module
- Unplug the ignition coil module's 4-pin connector.
- Connect the test lamp to:
- pins 4 and 3 (cyl. 1-4)
^ Pins 4 and 1 (cyl. 2-5)
or
^ pins 4 and 2 (cyl. 3-6)
- Turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "IGNITION CYL X-Y"
The command activates the relevant ignition coil at a frequency of 0.5 Hz for 30 seconds. The test lamp should flash.
Test lamp flashing?
YES: Change the ignition coil module and continue with point 8.
NO: Repair or replace the lead in question and proceed to point 8.
5. Check the spark plugs
- Remove the relevant spark plug and check its condition visually.
Is the plug OK?
YES: Continue with point 6.
NO: The electrode gaps are wider than 1.4 mm or otherwise obviously wrong. Change the spark plugs and continue with point 8.
6. Check the compression
- Carry out a compression test on the relevant cylinder.
Is the compression OK?
YES: Continue with point 7.
NO: Continue fault diagnosis in the Basic Engine.
7. Check the fuel flow capacity of the relevant injector
- Check the flow capacity.
Is the flow capacity OK?
YES: Continue with point 8.
NO: Change the injector. Then continue with point 8.
8. Final check
- Clear the diagnostic trouble code.
- Implementation of driving cycle:
^ While the engine is warming up, drive the car at varying engine loads and rpm. Make a point of driving with the engine at high revs.
- Evaluation of driving cycle:
^ Check whether the diagnostic trouble code has recurred.
Has the diagnostic trouble code recurred?
YES: Continue as described at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO: The steps taken to rectify the fault were correct.