Cummins fault code 686

What it means

Cummins' description: Turbocharger 1 Speed - Data erratic, intermittent or incorrect.

SPN 103 is Engine Turbocharger 1 Speed. FMI 2 means the signal is jumping around, dropping in and out, or doesn't make sense compared to other readings.

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: Cummins Tier 4 Fault Codes. Always confirm with Cummins service information (QuickServe) for your engine serial number.