Cummins fault code 768

What it means

Cummins' description: Output Device Driver (VGT or Transmission shift PWM signal).

SPN 923 is Output Device Driver (VGT or Transmission shift PWM signal). FMI 11 means the ECM detected a fault in this system but can't pin down the exact type. Further testing is needed.

The turbocharger forces air into the engine. Most modern Cummins engines use a variable geometry turbo (VGT) with an electronic actuator. The ECM watches intake manifold pressure, turbo speed and compressor temperatures to control boost.

What the lamp means

An amber (yellow) warning lamp means the engine can usually keep running, but the fault should be repaired soon, ideally the same day.

Common causes

The sensor reading itself is out of range or the condition is real, so look at the system:

• Boost leak: split charge air hose, loose clamp, cracked charge air cooler
• VGT vanes sticking from soot
• Worn or damaged turbo
• Clogged air filter or intake restriction
• Exhaust restriction from a plugged DPF

What you can check before calling

• Listen for a new hiss or whistle under load, a typical sign of a boost leak
• Check charge air hoses and clamps for oil or soot
• Check the air filter restriction indicator
• Notice whether power loss happens only under heavy load or on hills

Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers.

Engines and sources

Cummins uses the same fault code numbers across its electronic engines, including on-highway models like the ISB/B6.7, ISL/L9 and ISX/X15, though not every code applies to every engine or software level. Source: Diagnostic Fault Codes for Cummins Engines. Always confirm with Cummins service information (QuickServe) for your engine serial number.