First off, the P0688 code. What causes it to set?
- With ignition key on. Battery voltage greater than 10.0 Volts.
- The Powertrain Control Module (PCM) detects an open or short to ground in the (K51) ASD Relay control circuit. One Trip Fault. Three good trips to turn off the MIL.
OK so an open or short to ground on the relay control wire. That would make sense, the ASD relay supplies power to the fuel pump, injectors, coils etc...
So if the relay control wire was open you'd never see power at these components.
As you see later this code doesn't look only at the K51 circuit but seemingly the ASD circuit as a whole.
Some additional diagrams.
This one isn't that intuitive, the way the diagram is laid out and how at first glance it makes you think that the TIPM provides power to the injector and coil fuses.
When you get to here it makes a bit more sense. You can see the K51 control wire and the A935 fused power wire.
So it's time to locate the ASD relay.
Which is in here.
In the left front fender well... You can see where this is going...
What was left of the spade connector that goes to the radiator fan relay.
Here's an after fix photo.
Blast that with contact cleaner to clean it up a bit and smother it in dielectric grease...
Where the blue relay (radiator fan) is, the red/light blue wire is the one that rotted away. There was so much corrosion voltage dropped to 1v.
Like in the third wiring diagram you can see the ASD relay pulls power for the coil from the radiator fan relay.
Unfortunately no before fix pictures... It didn't really occur to me to document this until I was done. This fix applies to a range of Chrysler products that use this platform.
Who knows why the relay box isn't water proof. There aren't even weather pack seals on the bottom as you can see in the last picture. There is a lower and upper cover (not shown) but neither is water tight.