Hi, My Mini R56 gave off a P0303 code over a week ago. I pulled the plugs and after almost 12,000 miles they were worn down quite far. I installed a new set of plugs, cleared the OBD error and drove the car but the error came right back after a short distance. Pulled the plugs back out the No 3 plug was clean. I connected the coil and plug from cylinder #3 into the #1, 2 & 4 connectors and got spark on those but not No 3. Is there any chance the severely worn plug could have damaged the ECU? I unplugged the battery for a couple of hours too just in case I might clear something else...

Thanks

 

If you put #3 coil in another cylinder and ran the car and it still had #3 misfire fault you more likely have a cylinder problem. I'd do a compression and leak down test to make sure. Also in rare cases carbon build up on cylinder 3 intake could cause it, but rare.

 

I would check the wiring at the connector for the coil. You could also do a comparison resistance check to determine if there is a problem in the circuit. I.E. compare resistance reading between a known good circuit to the #3. Although not impossible it is highly unlikely that it is the actual ECU itself. A more definitive circuit test would be to check between the coil connector and the ECU connector to determine if there is a broken wire. However, to do so you will need a wiring diagram.

 

Just wanted to mention the search function brought this topic up - P0303 error. Cleared the error with my cheap ODB reader, came back right away. Swapped the coils between the two middle cylinders (of course leaving the wires going to the same cylinder as before) and it came back with a P0302 error which tells me I had a bad coil - the problem followed the coil from cylinder #3 to #2.

$52 spent at an auto parts store on a replacement Duralast coil and all was good. Saved myself $100's of dollars at the dealer on my Justa.

Now the OP did the same test and found that the problem did not follow the coil or the plug, a whole 'nother situation where something else had to be done, but I wanted to say sometimes it really is this simple to fix this code yourself in minutes.

 

Yep sounds like the coil might not be getting any voltage from the wiring harness, check continuity.

 

Just checking, but P0303 is cylinder 3 misfire? That is very different from "no spark".

Just for clarification, are you hearing a misfire, is this constant or intermittent? Does the car seem to run ok, or is it running on 3 cylinders all the time? If in doubt, unplug the coil from cylinder 3 and drive the car, is that the same or different?

No spark implies there is no current getting to the plug. As this has not changed with a new plug and coil, and with a known good plug and coil, then this is most likely wiring related.

However, if it is an intermittent misfire that has not corrected with a good plug and coil pack, then this is whole different ball game. This could well be something internally wrong inside that cylinder, valve burnt out etc etc

 

If you do not have any voltage going to that coil you will get a P0303 code “misfire on cylinder 3). I have the same issue. Spark plugs 1,2 & 4 are all black (not good) but spark plug 3 is clean, all 4 are brand new. I am going to start a thread on my issue. Welcome to owning a mini lol

 

Hi Scolinc,
Did you find root cause of your issue. I have a similar issue and see no spark in # 3 but spark in 4.
Compression comes out fine in all cylinder and have changes injectors etc.
Code read 2FAA - Cylinder 3 combustion period too short and the car is in limp mode and catalytic converter is overheating as fuel is getting burnt there.

 

If you swap coils 3 and 4, does the misfire code follow coil 3?

 

Have you resolved the issue? I have exactly the same as you had, no spark in # 3 and code read 2FAA. Please help!

 

In this case, the first thing that scolinc should have checked is the wire between coil #3 and the DME. In contrast, you should start by checking spark plug #3 and coil #3.

 

Thanks for the info and help. So far checked the ignition coil, spark plug and all in good. Confirmed there is power to the coil but not firing the spark on #3. Checked all the ECU connectors and pins are good condition. The signal wire should be from connector 1 but just not sure which pin/wire to check the continuity. Just hopping the ECU not fired.

 

What year and model is your Mini?
How did you check and rule out spark plug and coil #3?

 

I have a 2013 R56S with N18. I switched around the coils and spark plugs, the code stays with #3. I removed the coil and spark plug, and start the car with the coil and plug hooked on the scene to the ground and could not see any spark.

 

With KOEO, what is the voltage reading at the coil #3 power wire (using the - battery post as ground) versus the voltage reading across the two battery posts?

Below is the circuit diagram for the N18. As you can see, coil #3 signal wire runs to pin 13 of DME connector C (X60232). Test the coil #3 signal wire for both continuity and short to ground between the coil and DME connector.

 

Battery is 12.22V. Measure on the plug is 12.15V. Measure Plug + to the battery - is 12.17V

 

No problem here^.

 

In your expertise, possible to be wire or fried ECU? It was just happen so suddenly while driving, thus I think less possible to be the broken wire; however, after examined the #3 coil connector I found the green wire (Positive) the skin is broken and wire could be seen. Very bizarre!

 

Either is possible. Coil pin 2 is the coil ground wire, which must also be considered and tested.
Don't make assumptions. Just do the logical electrical troubleshooting. If you do, answers will come.

Post a clear picture. Somebody may have erred by poking through the wire insulation for a voltage test.