Help p0351 2008 848

akunochi

akunochi

Joined Jun 2014
181 Posts | 55+
North Carolina
I went riding to see if I could further diagnose the issue with my wife's 848. From around 5.5k to 6.8k the ignition sounds like it is breaking up.

I came back and pulled DTC with ducati diag. I recieved a P0351 primary secondary circuit malfunction.

I've checked and reset the TPS already as well.

Can anyone explain what this means besides bad primary coil/open circuit/ground. Any experience with this and where to begin?
 
Checking hertz with a Fluke there is a signal between 120-125 from the PCM on brown/white wire on both
 
If I got that error code and symptoms I would be looking for carbon arcing between the coil primary (where + connects) and the secondary (where the high tension lead goes in).

This normally indicates that the resistance of the lead has increased to the point where it cannot allow the passage of the spark.

Fix: Replace HT leads on both cylinders and coil/s if damaged (cracked post where HT lead goes in).

HT leads have a nominal resistance in ohms of say 4000 to 8000/ft. Heat degrades them and the resistance increases markedly.
 
Adrian I'm sorry but can you help me identify these points. I am following the wire from my battery + which goes to the little black cylinder. I assume this is my coil primary. But what is the HT?

There is only one cable coming off my coil with three wires. Yellow black and red on the coil side, borwn white, black and grey on the wiring harness side.
 
Last edited:
The HT lead goes from the secondary winding of the coil to the spark plug (the big wire).

I'm not familiar with the bike in question or the colour codes in the wiring harness but you will have a + and a - (earth) wire as a minimum. The other wire probably goes to a computer to monitor its operation - hence the production of the fault code. Coil ignition systems haven't changed much over the years. Apart from looking different, they still perform the same functions and still suffer the same faults.

If you aren't familiar with how coils work then I would look it up on Wikipedia and then you will understand how simple they are.
 
No I'm tracking how the coils work. I'll take another look in the AM.

I also found that the voltage regulator is smoked. .8v output out.
 
Already replaced the plugs. Thanks for the suggestion though.
 
Akunochi,
Ducati have the handbooks available on their website for all models less than 10 years old. There is a wiring diagram in the back of the handbook which should help.

I looked at a 2014 848 which had a 3 pin plug to the coil on each cylinder.
Brown/White = pin 1
Black = pin 2 = Earth
Grey/Green or Grey/Brown = pin 3. This is power from ECU through the ballast resistor to the coil primary. The ECU switches the power to the primary on and off to induce a large voltage in the secondary winding.

The handbook for your wife's bike should show the correct colour codes.

Hopefully someone more familiar with this bike can help you more.
 
So I got the fault diagnosed to the "A" ignition circuit which should be the horizontal coil. I swapped the vertical and horizontal coils and the problem is 10x more noticeable. At this point I think it is the coil from the horizontal or the ecu. I have a set of coils coming in.
 
If your regulator is smoked...what is the battery voltage?

If your battery gets too low the ignition system will not get enough power to operate properly. I had this problem on an R1. As the battery ran down I lost the electronic speedo and later the engine started to misfire and it stopped altogether.

To add insult to injury I was booked for speeding as I had no idea what speed I was doing. The cop didn't care that the bike had a fault. He was too interested in the revenue and promotional prospects.

Charge your battery fully and see if the same problem occurs.
 

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