SPN 679/FMI 7
The fault condition is typically related to a Pressure Limiting Valve (PLV) staying open. The pressure limiting valve will open when rail pressure is above 1150 bar. The MCM will command a lower rail pressure trying to force the pressure limiting valve closed. If the pressure limiting valve does not close, a fault code is generated. The condition that caused the PLV to open must be addressed.
Check as follows:
- Check for multiple codes.
- If additional fault codes are present with 679/7, service the additional fault codes first.
- If only 679/7 is present, go to the next step.
- Using DDDL, monitor rail pressure at idle.
- If rail pressure is above 900 bar, check for a damaged needle return line and a damaged line (fuel rail to injector). Repair as necessary. Refer to "16.1.1 Verify Repairs" .
- If rail pressure is below 900 bar, go to next step.
- Increase engine speed to 1800 rpm and check the rail pressure.
Verify repairs as follows:
- Turn ignition OFF.
- Reconnect any electrical connections that were disconnected to perform the diagnosis.
- Clear codes with DDDL 7.0 or latest version.
To avoid injury from inhaling engine exhaust, always operate the engine in a well-ventilated area. Engine exhaust is toxic.
- Start and bring engine up to operating temperature (over 140°F/60°C).
- Verify operation is satisfactory and no warning lamps illuminate. If warning lamps illuminate, troubleshoot the codes. If assistance is required, call the Detroit Diesel Customer Support Center at 313–592–5800.
|DD15 Fuel System Technician's Guide - DDC-SVC-MAN-0037|
|Generated on 10-13-2008|