DD15 Troubleshooting – Section 64.1 SPN 679/FMI 7

Section 64.1
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:‪

1. Check for multiple codes.
   1. If additional fault codes are present with 679/7, service the additional fault codes first.
   2. If only 679/7 is present, go to the next step.
2. Using DDDL, monitor rail pressure at idle.
   1. 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 "64.1.1 Verify Repairs" .
   2. If rail pressure is below 900 bar, go to next step.
3. Increase engine speed to 1800 rpm and check the rail pressure.
   1. If rail pressure is above 900 bar, check for a damaged needle return line, a damaged amplifier return line and a damaged line (fuel rail to injector). Repair as necessary. Refer to "64.1.1 Verify Repairs" .
   2. If rail pressure is below 900 bar, replace the PLV. Refer to "64.1.1 Verify Repairs" .

Section 64.1.1
Verify Repairs

Verify repairs as follows:‪

1. Turn ignition OFF.
2. Reconnect any electrical connections that were disconnected to perform the diagnosis.
3. Clear codes with DDDL 7.0 or latest version.

   ENGINE EXHAUST ‪
   To avoid injury from inhaling engine exhaust, always operate the engine in a well-ventilated area. Engine exhaust is toxic.‪

4. Start and bring engine up to operating temperature (over 140°F/60°C).
5. 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.