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DTC codes / C05xx · Brakes, steering and suspension / C0596

C0596Brake Booster Motor A Current Sensor Circuit Range/Performance

C0596 indicates that the antilock brake system (ABS) control module has detected an out-of-range or erratic current signal from the brake booster motor's current sensor circuit. The computer expects a specific current draw pattern when the booster motor runs, and the measured value falls outside that expected range or performance window.

SystemChassis
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • Illumination of the ABS warning light, often accompanied by the traction control and stability control lights
  • A hard or stiff brake pedal with reduced power assist, requiring noticeably more effort to stop the vehicle
  • The brake booster motor may run continuously or not at all, depending on the nature of the fault
  • A humming or whirring noise from the brake booster area that persists after the brake pedal is released
  • Often no symptoms besides the warning light, with normal brake feel and function
  • In some cases, a stored code with no drivability complaint until the system performs a self-test

Common causes, most likely first

  1. Faulty brake booster motor current sensor, either internally shorted or producing a skewed signal
  2. Damaged or corroded wiring and connectors in the current sensor circuit, including chafed harnesses near the booster
  3. Poor ground connection for the brake booster motor or the current sensor return circuit
  4. Failed brake booster motor drawing excessive current or binding mechanically, which distorts the current signature
  5. Contaminated or degraded brake fluid affecting booster motor load and current draw
  6. A failing ABS control module that misinterprets a valid current sensor signal
  7. Aftermarket or incorrect brake components installed previously that alter the expected current profile

How to diagnose and fix it

  1. Connect a scan tool and retrieve all ABS and body control module codes, then record freeze-frame data for C0596 to understand the conditions when it set
  2. Visually inspect the brake booster motor, current sensor, and all related wiring and connectors for corrosion, chafing, or loose pins
  3. Measure the current sensor reference voltage and signal voltage at the sensor connector with the key on and compare to manufacturer specifications
  4. Perform a voltage drop test on the booster motor power and ground circuits under load to rule out excessive resistance
  5. Command the brake booster motor on with the scan tool and observe live current sensor data to verify the signal tracks motor operation smoothly
  6. If the sensor signal is erratic but wiring is good, replace the brake booster motor current sensor or the motor assembly as required by the manufacturer's service procedure
  7. Clear codes and perform a road test with ABS self-test activation to confirm the repair and ensure the code does not return

What the current sensor really monitors

  • The current sensor does not measure brake fluid pressure; it measures electrical current drawn by the booster motor, so a mechanical brake problem can still set this code if it changes motor load.
  • A weak or failing battery or charging system can cause the booster motor to draw abnormal current during self-test, setting C0596 even though the brake system itself is healthy.
  • Technicians often replace the ABS module when the real fault is a chafed wire behind the booster that only shorts when the engine moves under torque.
  • Some vehicles run the booster motor briefly after the key is turned off, and a current sensor that fails only when cold can set C0596 intermittently with no warning during a warm shop visit.
  • After replacing the booster motor or sensor, some manufacturers require a calibration or learn procedure for the current sensor, and skipping it will immediately reset the code.

Can I keep driving with C0596?

The vehicle remains driveable because the base hydraulic brakes still function, but you should avoid heavy braking or emergency stops until the fault is repaired. If the brake pedal feels hard or assist is inconsistent, limit driving to low speeds and arrange service promptly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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