What does it mean?
C1098 is a Chassis (ABS, traction control, steering) fault code. It indicates: ABS Hydraulic Pump Motor Circuit Failure . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- ABS warning lamp on, sometimes only after a hard braking event
- Pump sounds weak, rough or runs longer than usual during the self test
- ABS cuts out mid event and the pedal feels hard or pulsates oddly
- Stability and traction control unavailable
- Fault appears in cold weather and clears once the vehicle warms up
- Longer stopping distances on slippery surfaces
Likely causes
- High resistance in the pump motor supply or ground from corroded terminals
- Worn brushes or a partially open armature making the motor draw the wrong current
- Ageing pump relay with pitted contacts and an unstable voltage drop
- Old, contaminated or moisture laden brake fluid making the pump work harder than normal
- Corrosion inside the hydraulic control unit connector after years of road salt
- Weak battery or charging fault leaving the motor short of voltage under load
- Internal fault in the ABS control module motor circuit
How to fix it
- Test battery condition and charging voltage, since a weak supply mimics a motor fault
- Perform voltage drop tests on the pump feed and ground while the pump is commanded
- Command the pump with a scan tool and compare current draw and run time to specification
- Inspect and clean the hydraulic unit connector and the module ground point
- Check brake fluid condition and moisture content, and bleed the system if it is neglected
- Substitute or bench test the pump relay
- Replace the pump motor or hydraulic control unit if the electrical circuit tests good, then bleed and code the system