Cummins fault code 769

What it means

Cummins' description: Brake Switch Circuit - Voltage above normal, or shorted to high source.

SPN 597 is Brake Switch. FMI 3 means the voltage on the circuit is higher than possible for a good sensor, usually an open signal wire, a short to a power wire, or a failed sensor.

The accelerator pedal has position sensors and an idle validation switch so the ECM knows exactly what the driver is asking for. Cruise control, brake and clutch switches, PTO and vehicle speed inputs are also monitored.

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

FMI 3 is an electrical or signal fault, so start with the circuit:

• Accelerator pedal sensor worn or failed
• Pedal connector corroded or loose
• Brake, clutch or cruise switch out of adjustment or failed
• Vehicle speed sensor or wiring fault

If the circuit checks out, the reading may be real. Other possibilities: pedal sensors disagreeing with each other; switch inputs that don't make sense together, like brake and throttle at once.

What you can check before calling

• Check whether the engine stays at idle no matter what you do with the pedal
• Look at the pedal connector under the dash
• Check whether cruise control works

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

Engines and sources

Listed by Cummins for: QSX 15, QSG 12. 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: Cummins Tier 4 Fault Codes. Always confirm with Cummins service information (QuickServe) for your engine serial number.