Originally Posted by Evelyn
I got this dtc along with a few other...
And the others are?
From personal experience, when my car displayed this code (and it only did so after running like crap for an extended period before the CEL came on) the symptoms were as described by the OP. The code is very specific; it has only a few possible causes.
Some background: The coil is fed by a three wire black plastic electrical connector. The thicker gauge middle wire (green/blue) provides 12V to the coil. The two outer wires (black/orange and black/green) are the signal switching wires that cause the coil to fire either cylinders 1 and 4 or 2 and 3. (The Focus uses a wasted spark ignition system so the coil fires plugs in pairs.)
DTC P0351 usually means of the three wires, black/green has an intermittent or is broken. (Driver circuit A - cylinders 1 and 4)
DTC P0352 usually means of the three wires, black/orange has an intermittent or is broken. (Driver circuit B - cylinders 2 and 3)
(I think I've got the sequence/colours right - anyway you get the idea.)
Be forewarned, the wires can break within the connector itself so giving the wires a gentle but solid tug is required. (Can't just peer at them.) Cracked insulation / corrosion and brittle wires are a bad sign.
You can effect a temporary repair by pulling the connector apart (with great difficulty - ask me how I know) and joining each pin to its respective connector separately. Each pin must be properly isolated from its neighbour, obviously.
A proper complete repair requires Motorcraft part # WPT 517 (also known as Ford part # 3U2Z14S411TNA) or a good connector ("pigtail") from a scrap car.
It needs to be spliced into the wiring harness in place of the old connector. The three wires provided on the Motorcraft part are black so note the wiring order before starting the job.
Connector pics in this link:
How to Fix Pigtails connectors on Ford Focus
If the coil connector looks good, then the intermittent connection or break is within the coil itself and coil replacement is required. You can sometimes see cracks in the bottom of faulty coils, I'm told, but I haven't seen this for myself. You'll want to look at the connector first; it's cheaper than coil replacement (for new parts anyway.)
Failing all of the above, the wiring fault is probably within the wiring harness between the PCM and the coil connector (rare). Check for the presence of 12V at the green/blue wire and for continuity in the switching wires.
Black/green - PCM connector pin 52
Black/orange - PCM connector pin 26