24V Cummins Basic Diagnostics

Use this article to diagnose driveability problems existing when a hard Diagnostic Trouble Code (DTC) is not present.

Engine Difficult To Start Or Will Not Start
(Exhaust Smokes While Cranking)

• Check for low fuel level.
• Check for low battery voltage.
• Check for plugged fuel filter.
• Check for poor quality or improper grade of fuel.
• Check fuel tank venting.
• Check for low fuel pressure.
• Check for air in fuel system.
• Check for fuel lift pump malfunction.
• Check for fuel inlet restriction.
• Check for kinked or restricted fuel line.
• Check for kinked or restricted fuel return passage or fuel return line.
• Check for incorrect injectors.
• Check for incorrect injector shim thickness.
• Check for injector malfunction.
• Check for fuel connector leaking fuel.
• Check for engine speed sensor and/or circuit malfunction.
• Check for moisture in harness connectors or corroded terminals.
• Check for internal engine damage.
• Check for air intake restriction.
• Check for exhaust restriction.
• Check for fuel inlet temperature too high.
• Check valve lash adjustments.
• Check for ignition switch output voltage low and/or open.
• Check starting accessories for cold weather such as engine block heaters or fuel heaters (if equipped).
• Check fuel pump overflow valve.
• Check for low engine cranking speed.
• Check for electrical noise.

Engine Difficult To Start Or Will Not Start
(No Exhaust Smoke While Cranking)

• Check for low fuel level.
• Check for poor quality or improper grade of fuel.
• Check for plugged fuel filter.
• Check fuel tank venting.
• Check for low fuel pressure.
• Check for air in fuel system.
• Check for fuel lift pump malfunction.
• Check for fuel inlet restriction.
• Check for fuel injection pump supply voltage open or low voltage.
• Check for kinked or restricted fuel inlet line.
• Check for kinked or restricted fuel return passage or fuel return line.
• Check for incorrect injectors.
• Check for incorrect injector shim thickness.
• Check for injector malfunction.
• Check for fuel connector leaking fuel.
• Check for engine speed sensor and/or circuit malfunction.
• Check for moisture in harness connectors or corroded terminals.
• Check for Sentry Key Immobilizer Module (SKIM) issues.
• Check for low battery voltage.
• Check for ignition switch supply voltage low or open.
• Check for electrical noise.
• Check fuel injection pump.
• Check ECM.
• Check for internal engine damage.

Engine Surges At Low Or High Idle

• Check for low fuel level.
• Check for plugged fuel filter.
• Check for poor quality or improper grade of fuel.
• Check for fuel tank venting malfunction.
• Check for low fuel pressure.
• Check for air in fuel system.
• Check for fuel lift pump malfunction.
• Check for restricted fuel inlet.
• Check for kinked or restricted fuel inlet line.
• Check for kinked or restricted fuel return line.
• Check for incorrect injectors.
• Check for incorrect injector shim thickness.
• Check for malfunctioning injectors.
• Check for leaking fuel connection.
• Check for faulty fuel injection pump.
• Check for malfunctioning or out of calibration accelerator pedal.
• Check for damaged vibration damper.
• Check for engine speed sensor and/or circuit malfunction.
• Check for vehicle speed sensor and/or circuit malfunction.
• Check for incorrect transmission clutch operation.
• Check for dragging brakes.
• Check for transmission malfunction.
• Check for cooling fan cycle time malfunction.
• Check for turbocharger malfunction.
• Check for Bus communication malfunction.
• Check for moisture in harness connectors or corroded terminals.
• Check for internal engine damage.
• Check for electrical interference (noise).
• Check for excessive load at idle.
• Check for incorrect or malfunctioning clutch.

Engine Surges Under Load Or Operation Range

• Check for low fuel level.
• Check for plugged fuel filter.
• Check for poor quality or improper grade of fuel.
• Check for fuel tank venting malfunction.
• Check for low fuel pressure.
• Check for air in fuel system.
• Check for fuel lift pump malfunction.
• Check for fuel inlet restriction.
• Check for kinked or restricted fuel inlet line.
• Check for kinked or restricted fuel return line.
• Check for incorrect injectors.
• Check for incorrect injector shim thickness.
• Check for malfunctioning injectors.
• Check for leaking fuel connection.
• Check for malfunctioning or out of calibration accelerator pedal.
• Check for engine speed sensor and/or circuit malfunction.
• Check for vehicle speed sensor and/or circuit malfunction.
• Check for incorrect transmission clutch operation.
• Check for dragging brakes.
• Check for transmission malfunction.
• Check for cooling fan cycle time malfunction.
• Check for turbocharger malfunction.
• Check for Bus communication malfunction.
• Check for moisture in harness connectors or corroded terminals.
• Check for internal engine damage.

Excessive Black Smoke

• Check for dirty or plugged air filter.
• Check for restricted/leaking air intake system.
• Check for DTCs set or intermittent DTC malfunctions.
• Check for ECM or PCM not calibrated properly.
• Check for exhaust system restriction greater than specification.
• Check for poor fuel quality.
• Check for fuel injection pump malfunction.
• Check for fuel injector malfunction or leak.
• Check for fuel return system restriction.
• Check for intake manifold restriction.
• Check for manifold air pressure (boost) sensor circuit malfunction.
• Check for raw fuel inside intake manifold.
• Check for turbocharger air intake restriction.
• Check turbocharger for excessive carbon build-up on compressor wheel and/or diffuser vanes, wheel
  clearance out of specification or damage

Excessive Blue Exhaust Smoke

• Check for dirty or plugged air filter.
• Check for air intake system restriction.
• Check for air leak in intake between turbocharger and intake manifold.
• Check for restricted exhaust.
• Check for restricted turbocharger drain tube.
• Check for plugged crankcase ventilation.
• Check for worn or defective valve stems, guides or seals.
• Check for improperly gapped, worn or broken piston rings.
• Check for excessive cylinder bore wear.
• Check for cylinder damage.
• Check for piston damage.
• Check for turbocharger failure.

Excessive White Exhaust Smoke

• Check for air in fuel system.
• Check for coolant leak into combustion chamber.
• Check for DTCs set or intermittent DTC malfunctions.
• Check for block heater malfunction in cold weather.
• Check for engine coolant temperature sensor malfunction.
• Check for ECM not calibrated properly.
• Check for clogged or defective fuel filter.
• Check for poor fuel quality.
• Check for fuel heater or fuel heater temperature sensor malfunction.
• Check for malfunctioning or loose fuel injector.
• Check for fuel injection pump malfunction.
• Fuel injector restricted or blocked fuel injection or supply lines.
• Check for fuel transfer pump malfunction.
• Check for Intake/exhaust valves not adjusted properly (tight).
• Check for intake manifold heaters or intake manifold air temperature sensor malfunction.
• Check for internal engine damage.