Safe to driveDrivable, but watch it yourself
SPN 4029 is a manufacturer number outside the standard J1939 table: different makes can put different things under it. Below — how it is worded by International and Renault Trucks, and what the second half of the code (FMI) means.
| FMI 2 | Service Brake Circuit 1 Air Tank Drain Valve Switch — Service Brake Circuit 1 Air Tank Drain Switch Error |
| FMI 4 | No messages from the tachograph. Repair: Check the tachograph unit for faults, check the CAN bus communication with the tachograph, the resistance between the two wires is 60 ohms (pins 22, 49). |
| SPN 4029 FMI 24029/2 · 4029.2 | data erratic or intermittent |
| SPN 4029 FMI 44029/4 · 4029.4 | voltage below normal or shorted to ground |
Safe to drive. Below — how much time you have and what happens if you keep going.
This is an electrical fault: an open, a short or a bad contact in the sensor circuit. The value it measures is most likely fine.
You can drive. But until the circuit is repaired this system runs blind and cannot warn you about a real failure.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.