A fault code doesn’t yet mean the unit or sensor itself is faulty: often it’s the plug and connector leading to it.
What you can do yourself
- This is the pressure in the auxiliary equipment circuit, not the brakes. What it supplies depends on the vehicle.
- Check the brake circuit pressures on the dashboard: if they’re low or the low air pressure light is on, don’t drive.
- Check the compressor, the pressure regulator and air leaks (listen for hissing).
- FMI 2, 3, 4, 5 — the pressure sensor, its connector or wiring — go to an auto electrician.
- Electrics (sensors, valves, wiring, control unit) — to an auto electrician. Leaks and mechanical faults — to an air brake specialist.
Stop and don’t drive on if:
- The low air pressure light is on or the buzzer sounds
- The air pressure gauges on the dashboard are below the normal range or dropping
- The brakes have got worse, or the vehicle is braking by itself
Add the FMI — the second number of the code. It shows what exactly is wrong with the parameter.
Source: SAE J1939-71: J-1939 SA/SPN/FMI Descriptions (static.nhtsa.gov, MC-10141869)
The explanation comes from the error code reference in the AvtoElektrik PRO app.