Originally Posted by Th Dude
Thanks for your reply.
The code is P0303
Previous owner claims to have recently changed plugs, cleaned MAF, new 997tt coil packs, new air filter.
This is what it means:
510 Misfire, cylinder 3
• A cycle of 1,000 crankshaft revolutions is evaluated (for misfire
damaging to the TWC, 200 crankshaft revolutions). The misfire
rates are compared with a threshold value. If the misfire rate is
greater than the threshold value, a fault is recorded in the memory.
• The Check Engine Malfunction Indicator Lamp (MIL) is switched
on and stays on when the misfire rate lies above the threshold
value at which the emission limit values are exceeded during two
consecutive driving cycles (in the case of EOBD 3 driving
• If the misfire rate may lead to permanent damage to the TWC,
the Check Engine MIL flashes. If the misfire rate is no longer
reached during the first journey, the MIL goes out. If the rate is
reached during the next journey, the MIL flashes. If this misfire
rate is subsequently no longer reached, the MIL changes to a
♦ When using a block heater (for heating coolant), start and driving
off difficulties or misfiring can occur if the block heater was connected
for less than 4 hours.
♦ When the fuel tank is driven to empty, misfiring can occur. For
this reason the fuel level in the tank is also stored in the memory
when misfiring occurs. If the tank was nearly empty, there was
probably no fault. Erase fault memory and road test vehicle.
♦ In the event of a short circuit to B+ or ground in the oxygen sensors
ahead of the TWC, the mixture becomes too lean or too
rich. This can cause misfiring. If, in addition, an oxygen sensor
signal fault ahead of the TWC is stored in memory, first correct
this fault and then road test the vehicle.
Possible fault cause
♦ Fault in ignition system
♦ Fault in injection system
♦ Flat-base tappets (valve lift fault)
♦ Mixture too rich
♦ Mixture too lean