Low Line Pressure — Demand Exceeds Capacity
The SULLAIR-LOW-LINE-PRESSURE (Sullair WS Controller) diesel fault code means: Low Line Pressure — Demand Exceeds Capacity. This is a moderate severity code.
- DIY difficulty
- moderate
A $30 car code reader can't do diesel. The HD7000 reads full-system codes and does parked DPF regen, idle/speed-limit, and service resets from the cab — on everything from a 6.7 Cummins/Power Stroke/Duramax pickup to Class-8 trucks (Detroit, Paccar, CAT, Volvo, Mack, International).
Full-system 6/9/16-pin diesel scan tool for Cummins, Paccar, CAT, Detroit and more — plug-and-play, no subscription. A cheaper way to read heavy-duty codes a basic OBD2 scanner skips entirely.
Affiliate links — we earn a commission at no extra cost to you.
Common Symptoms
- WS display shows Low Line Pressure
- Air tools or process starved downstream
Probable Causes (Ranked by Likelihood)
- Demand exceeds compressor capacity High
- Leaks or open lines in the air supply High
Frequently Asked Questions
Is the compressor broken?
Usually not — the factory's causes are demand exceeding capacity and supply-line leaks. The machine is telling you it cannot keep up, which is a system problem before it is a compressor problem.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
The WS Controller is fitted to Sullair STATIONARY electric shop compressors. Portable towable Sullair units (185-class and similar) use different engine-driven controls and a different fault system — this page does not apply to them.
Reduce demand or increase capacity — this is a sizing/usage condition, not a machine fault.
Check the supply lines for leaks or open drops and repair as necessary.
Per the factory manual: after resolving a fault condition, press the STOP pad to clear the FAULTED state. If the problem persists after the recommended checks, consult your Sullair distributor or factory service.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- Sullair WS Controller User Interface Manual, P/N 02250165-411 (Table 5-1 Troubleshooting Guide)distributor-hosted copy of the official Sullair manualdistributor-hosted copy of an official Sullair factory manual
Commonly Affected Vehicles
- Sullair STATIONARY electric rotary-screw compressors with the WS Controller (including VSD packages)
Related Codes
Explore More
Was this helpful?
Send this to whoever is fixing the truck — your tech, or the person asking what the fault means.