C1253

Symptoms

• ABS
• VSC/traction
• and brake warning lights on
• braking performance can be affected
• in some failure modes the pump runs continuously (relay stuck on).

Probable causes

• 1) Faulty pump motor relay (open coil, welded contact, or short keeping it always on). Per Toyota detection logic
• the code sets when: an open in the relay coil is detected for more than 1 second after ignition ON
• the relay is always ON due to a short for more than 1 second
• the relay does not turn ON for more than 0.2 seconds when low pressure is detected or while the pump motor operates
• or the relay is always ON due to a welded contact for more than 2 seconds. On many models the relays are internal to the skid control ECU / actuator assembly. 2) Wiring or connector damage/corrosion in the pump motor circuit. 3) Failing brake actuator with an internal leak causing the booster pump to run continuously (a known Lexus brake actuator defect is cited, where a rubber seal was too soft to hold hydraulic pressure).

Diagnostic steps

1. Read chassis codes with a scanner that accesses the ABS/skid control ECU and note all codes present.
2. Visually inspect the brake booster pump motor, its relay, wiring, and connectors for damage, corrosion, or broken/bent/pushed-out pins.
3. Test the brake booster pump motor with a multimeter to determine if it is functioning correctly; repair or replace damaged wiring or connectors.
4. With an advanced scan tool (e.g. Toyota Techstream), perform an active test on the motor relay and monitor the accumulator pressure sensor data - a rapid pressure drop after the pump shuts off confirms an internal leak in the actuator.
5. If the relay circuit is faulty and the relays are integrated in the skid control ECU/actuator assembly, replace the assembly per the service manual.
6. Clear codes and verify the ABS/VSC/brake lights stay off and the pump cycles normally. Do not keep driving with this code active - it affects brake system operation.