3408705 | Genuine Cummins® Pressure Switch For ISB/QSB

• Cummins® ISB / QSB Series: 5.9L and 6.7L mid-range diesel engines (used in commercial trucks, buses, and industrial machinery).

• Cummins® ISC / QSC Series: 8.3L diesel engine platforms.

• Commercial Truck Applications: Freightliner® (M2 106, FC70), International® / Navistar® (DuraStar / 4000 Series), Kenworth®, and Peterbilt® medium-duty trucks powered by ISB or ISC engines.

• Bus Chassis Fitment: Blue Bird® and Thomas Built Buses® equipped with ISB 5.9L / 6.7L engines.

• Off-Highway & Industrial Equipment: Construction, agricultural, and power generation units (G-Drive / Gensets) powered by QSB / QSC engines.

1. What is it?

Part is a threshold-based electrical switch (rather than a continuous variable sensor). Installed directly into a pressurized fluid or air passage (such as oil or fuel lines), it opens or closes an internal electrical contact when pressure reaches a specific pre-set threshold.

2. Core Functions & Technical Features

• Binary On/Off Signal: Unlike a transducer that continuously sends changing pressure values, this switch operates as a simple binary circuit trigger (Normally Open or Normally Closed) to signal whether pressure is above or below safe operating limits.

• Warning Light & Gauge Actuation: Triggers low-pressure dashboard indicator lamps or chimes to alert the driver immediately when system pressure drops dangerously.

• ECM Safety Interlock: Transmits a discrete signal to the Cummins® Engine Control Module (ECM) to restrict engine operation or prevent starting under zero-pressure conditions.

• Corrosion-Resistant Housing: Features a heavy-duty threaded metallic body built to withstand intense engine vibration, high operating temperatures, and harsh engine bay environments.

1. False Low Pressure Warning Light / Alarm

• Symptom: The low oil or fluid pressure warning light stays permanently illuminated on the dashboard or flickers erratically at idle, even though physical fluid levels and actual system pressures are completely normal.

• Cause: Internal electrical contacts become welded closed, oxidized, or stuck due to spring mechanical fatigue.

2. Warning Light Fails to Turn On During Engine Pre-Check

• Symptom: The pressure indicator light fails to illuminate when turning the ignition key to the "ON" position (key-on, engine-off self-test).

• Cause: Broken internal contacts or open-circuit failure inside the switch preventing circuit ground completion.

3. Nuisance Engine Derate or No-Start Condition

• Symptom: The engine ECM limits horsepower output or prevents starting because it incorrectly detects zero pressure in the monitored line.

• Cause: The switch fails to send the required closed-circuit signal to the ECM after the engine cranks and builds operating pressure.

4. Fluid Leaking Through Electrical Terminals

• Symptom: Oil or fluid moisture found leaking directly out of the electrical connector body or pin area.

• Cause: Ruptured internal sealing diaphragm allowing pressurized fluid to penetrate the internal electrical housing.