SPN 789 FMI 7
STOP
Trailer ABS
ABS is disabled: the brakes still work, the assist does not.
SPN 789 FMI 7: ABS is disabled: the brakes still work, the assist does not. Stop: this is a stop-now code. Park safely and do not keep driving until it is checked.
Electrical · Brakes / ABS
Can I keep driving?
Stop: this is a stop-now code. Park safely and do not keep driving until it is checked.
What it means
ABS system fault: the module disabled anti-lock. Service brakes still work, but without ABS or traction control. This is a DOT inspection item and an out-of-service condition.
Most likely causes
Dirty or misadjusted wheel speed sensor
Very likely
Sensor harness chafed on the axle
Very likely
Damaged tone ring
Likely
Internal ABS module failure
Less likely
Tests, cheapest and most decisive first
1. Measure wheel speed sensor resistance
Expected result: Between 1500 and 2500 ohms
Tool: Multimeter
2. Push the sensor to the tone ring and spin the wheel reading AC volts
Expected result: Over 0.2 V AC spun by hand
Tool: Multimeter
Related codes
Read it off your own dash
Take one photo and DERATE tells you whether you can keep driving.
Ask DERATE
DERATE assists. It does not replace inspection by a qualified technician.