International SA 33 SPN 871 FMI 18: AC - Service now low charge

SA 33 SPN 871 FMI 18 on International / Navistar trucks means: AC - Service now low charge. The failure mode (FMI 18) is “data valid but below normal range (moderately severe)”.

Code details

Manufacturer: International (Navistar)
Applies to: International / Navistar body controller (ESC) and multiplexed modules
Fault code: SA 33 SPN 871 FMI 18
J1939 SPN: 871
FMI: 18 — Data valid but below normal range (moderately severe)
Reporting module: Body Controller (source address 33)
Component / signal: Refrigerant Charge
Truck models in source: 3200, 4100, 4300, 4400, 7300, 7400, 7500, 7600, 7700, 8500, 8600, BE 200, CE Bus, CXT, DuraStar, LoneStar, MXT, ProStar, RXT, TranStar, WorkStar
Logical signal: BC_RCD_Temp_In_Raw_Si gnal, BC_RCD_Temp_Out_Raw_ Signal

Cause and when it sets

Cause: Data valid but below normal operating range - moderately severe level

What to do next

Read active and inactive codes with the OEM service tool (Diamond Logic Builder can clear previously active codes) and note the occurrence count.
FMI 18 tells the shop the type of failure to test for: data valid but below normal range (moderately severe).
Have a heavy-duty diesel technician confirm the fault against the engine or chassis service manual before replacing parts.