Ben,

These codes are for the LP system. E681 - - Electronic Pressure Regulator (EPR) Actuator Problem and E678 - Fuel Pressure at DEPR Higher Than Expected. Make sure you check each step. You may want to look at fuse 6 and 7 first before beginning. Good Luck.

Disconnect the DEPR connector CPS269 and measure voltage between socket 6 and B(-).
Is battery voltage present?
YES: Proceed to Step 2.
NO: Inspect 20A Fuse F6 and battery voltage input circuit for open or short. Inspect connectors CPS160 and
CRP15 for loose, damaged, or corroded terminals.
NOTE: Key in ON position.
2. Measure voltage between the DEPR connector CPS269, socket 3 and B(-).
Is ignition voltage present?
YES: Proceed to Step 3.
NO: Inspect 30A Start Fuse F7 and start switch for faults. Inspect ignition voltage circuit for open or short.
Inspect connectors CPS55 and CRP14 for loose, damaged, or corroded terminals.
NOTE: Key in ON position.
3. Measure voltage between the DEPR connector CPS269, socket 5 and B(-).
Is CAN HI voltage approximately 2.5 Vdc?
YES: Proceed to Step 4.
NO: Inspect CAN HI circuit for open or short. if voltage is 0 volts, the CAN HI circuit is shorted to ground or
open. If voltage is above 5 volts, the CAN HI circuit is shorted to power.
NOTE: Key in ON position.
4. Measure voltage between the DEPR connector COS269, socket 1 or 2 and B(-).
Is CAN LO voltage approximately 2.5 Vdc?
YES: Disconnect battery and proceed to Step 5.
NO: Inspect CAN LO circuit for open or short. if voltage is 0 volts, the CAN HI circuit is shorted to ground or
open. If voltage is above 5 volts, the CAN HI circuit is shorted to power.
5. Measure resistance between the DEPR connector CPS269, socket 5 and socket 1 or 2.
Is resistance 60 ± 6 ohms?
YES: No communication faults are present, connect battery and proceed to CAUSE B.
NO: If resistance is 120 ohms, the CANbus has an open circuit or a missing or damaged termination resistor.
If resistance is 0 ohms, the CANbus circuits are shorted together.
CAUSE B - DEPR FAULT
PROCEDURE OR ACTION:
1. Replace faulty DEPR.
END POSSIBLE CAUSES
ELECTRICAL SYSTEM Diagnostic Trouble Codes
Check the Service Manual section in Hypass Online for possible updates and check pertinent Gram