Diagnosing EPS Faults

When the EPS warning light comes on, the driver either has heavy steering, no assist at all, or intermittent assist that cuts in and out. This is not a guessing game. The EPS module stores detailed fault codes that tell you exactly what the system detected. Your scan tool is your first move — always.

Connect your scan tool and read codes from the EPS module specifically — not just the generic OBD-II codes. EPS faults are manufacturer-specific codes stored in the EPS or power steering control module. Common code categories: torque sensor signal faults, motor current faults, vehicle speed signal faults, battery voltage faults, and communication faults. Read freeze frame data if available — it tells you the conditions when the fault was set. Note whether the code is current or stored history. A current code means the fault is happening right now. A stored code may have been a one-time event.

The EPS motor draws significant current — 60 to 80 amps on some systems during parking lot maneuvers. A poor battery, corroded battery terminals, or a weak ground connection to the EPS module can cause the system to fault from low voltage under load. Check battery voltage at rest — should be 12.6 volts. Check voltage at the EPS module connector with the engine running and the wheel being turned — should stay above 13 volts. A voltage drop below the module threshold during a hard turn triggers a fault and disables assist. Fix the power supply issue before condemning EPS components.

Torque sensor faults are the most common EPS code. Use the scan tool to view live data for the torque sensor signal. With the steering wheel released and the vehicle sitting still, the torque sensor should read zero or near zero. Turn the wheel left — the value should increase smoothly in one direction. Turn right — it should increase smoothly in the opposite direction. If the signal is erratic, jumps, has dead spots, or reads an offset at center, the torque sensor or its wiring is faulty. Check the clock spring first — the ribbon cable inside the steering column that provides electrical connections while the wheel rotates. A damaged clock spring disrupts the torque sensor signal on many vehicles. Check the connector at the base of the steering column for corrosion or loose pins.

If codes point to the EPS motor — high current draw, motor circuit open, motor circuit short — verify the motor connections first. Check the motor connector for corrosion, melted pins, or water intrusion. On rack-assist systems, the motor sits under the vehicle and is exposed to road spray and salt. Corroded connectors are common. If the connector is clean and tight, check motor resistance between the motor terminals with the connector unplugged — compare to manufacturer specification. A motor that is mechanically binding from internal corrosion or debris draws excessive current and triggers overcurrent faults. On column-assist systems, check for binding in the steering column itself — a failing intermediate shaft or tight U-joint can increase the load on the motor and cause current faults.

The EPS module communicates with other modules over the CAN bus network — it needs vehicle speed from the ABS module and sometimes steering angle data. A communication fault code in the EPS module may not be an EPS problem at all. It may be a CAN bus issue, an ABS module fault, or a wiring problem on the network. Check for codes in all modules, not just the EPS module. A missing vehicle speed signal causes some EPS systems to default to maximum assist at all speeds or to disable assist entirely as a safety measure.