Hybrid Vehicle Brake System Problems & Solutions

No.	Brake System Problem	Common Symptoms	Possible Causes	Solution / Repair
1	Regenerative Braking Not Working	Little/no energy recovery	Motor, inverter, HCU or battery fault	Scan the hybrid system and diagnose the regenerative-braking circuit
2	Weak Regenerative Braking	Vehicle decelerates less than expected	Low battery SOC, battery temperature or system limitation	Check battery condition, temperature,e and control strategy
3	Regenerative Braking Intermittent	Regeneration works sometimes	Sensor, communication, or control fault	Check DTCs, sensors, and CAN communication
4	No Regenerative Braking During Deceleration	No battery charging during coasting	Motor-generator, inverter,rter or HCU fault	Check motor-generator and inverter operation
5	Regenerative Braking Cuts Out Suddenly	Unexpected change in braking feel	Battery full, temperature limit or fault	Check HV battery SOC/temperature and DTCs
6	Friction Brakes Doing Excessive Work	Brake pads wear quickly	Regenerative braking unavailable	Diagnose motor, inverter,erter and hybrid control system
7	Brake Blending Incorrect	Uneven or inconsistent braking feel	Brake ECU/HCU calibration or sensor fault	Perform system diagnosis and required calibration
8	Brake Pedal Hard	Excessive pedal effort	Brake booster or hydraulic-assist problem	Check booster, actuator, and hydraulic system
9	Brake Pedal Soft/Spongy	Long pedal travel	Air in hydraulic circuit or fluid problem	Inspect system and bleed brakes correctly
10	Brake Pedal Pulsation	Pedal vibrates during braking	Disc runout, ABS intervention,vention or rotor problem	Inspect discs and ABS operation
11	Brake Pedal Sensor Fault	Brake warning/DTC, incorrect brake response	Sensor or wiring failure	Test pedal sensor signals and replace if necessary
12	Brake Stroke Sensor Fault	Abnormal brake blending	Sensor calibration/wiring problem	Diagnose and calibrate/replace sensor
13	Brake Control ECU Fault	Brake warning or abnormal braking	ECU, power or communication fault	Scan ECU and verify power, ground,d and CAN
14	Brake ECU Communication Failure	Multiple warning lights	CAN wiring/module fault	Check CAN-H, CAN-L, connectors and termination
15	HCU Communication Fault	Hybrid/brake warning	CAN network or HCU fault	Diagnose communication network
16	Hybrid Control Unit Fault	Regeneration unavailable	HCU hardware/software problem	Scan HCU and perform manufacturer-approved repair
17	ABS Warning Light ON	ABS unavailable	Wheel sensor, ABS E, CU or hydraulic fault	Retrieve DTCs and ABS
18	ABS Not Operating	Wheels may lock during hard braking	ABS module, sensor or hydraulic fault	Test ABS ECU and wheel-speed signals
19	ABS Activates Unnecessarily	Pulsation during normal braking	Faulty wheel-speed signal or sensor	Inspect sensor, tone ring and wiring
20	Wheel-Speed Sensor Fault	ABS/ESC/regen warning	Sensor, wiring or tone-ring damage	Test sensor signal and replace damaged component
21	Wheel-Speed Sensor Signal Intermittent	Intermittent ABS warning	Loose connector, damaged wiring,g or contamination	Inspect wiring, tor and sensor
22	Wheel-Speed Sensor Tone Ring Damaged	Incorrect wheel-speed reading	Cracked/corroded tone ring	Repair/replace affected component
23	Brake Booster Failure	Hard brake pedal	Booster motor, vacuum or electrical fault	Diagnose booster and power supply
24	Electric Brake Booster Motor Fault	Warning and increased pedal effort	Motor/control failure	Test booster motor and control module
25	Brake Booster Communication Fault	Brake warning	CAN or module fault	Check communication and wiring
26	Hydraulic Brake Actuator Fault	Abnormal pedal/braking performance	Pump, valves, es or actuator ECU fault	Scan and test hydraulic actuator
27	Hydraulic Brake Pressure Too Low	Weak braking	Pump, leak or actuator problem	Check fluid, leaks and pressure generation
28	Hydraulic Brake Pressure Too High	Brakes drag/overheat	Stuck valve or control fault	Diagnose actuator and pressure-control circuit
29	Brake Fluid Leakage	Low fluid level	Hose, caliper, pipe, or actuator leak	Find and repair leak; restore fluid and bleed system
30	Brake Fluid Contamination	Poor brake performance	Moisture or contaminated fluid	Flush and replace fluid according to manufacturer specification
31	Brake Caliper Sticking	Vehicle pulls/brake overheating	Corrosion or seized piston/slider	Service or replace caliper
32	Brake Pad Excessive Wear	Grinding/noise	Caliper problem, driving conditions, or low friction-brake regeneration contribution	Inspect braking system and replace pads
33	Brake Disc Overheating	Burning smell/heat	Brake drag or excessive friction braking	Inspect caliper, pads, and hydraulic pressure
34	Brake Disc Warping/Runout	Steering/pedal vibration	Excessive heat or disc runout	Measure disc and replace/resurface as permitted
35	Brake Disc Corrosion	Noise/rough braking	Low friction-brake usage and environmental corrosion	Inspect and service/replace discs as required
36	Brake Pad Glazing	Reduced braking/friction noise	Excessive heat or light braking	Inspect pads and replace if necessary
37	Brake Caliper Pressure Unequal	Vehicle pulls to one side	Hydraulic restriction or caliper fault	Check hydraulic circuits and calipers
38	Brake Pulling to One Side	Vehicle moves left/right during braking	Unequal braking force or tire issue	Inspect calipers, pads, discs and tires
39	Yaw Sensor Fault	ESC/brake warning	Sensor calibration or wiring fault	Test and calibrate/replace yaw sensor
40	Vehicle Stability Sensor Fault	ESC/ABS warning	Yaw/lateral acceleration sensor issue	Scan sensor and perform calibration
41	Steering Angle Sensor Fault	ESC/ABS warning	Sensor calibration or wiring problem	Calibrate or replace sensor
42	Electronic Stability Control Fault	ESC warning, reduced stability control	ESC module, sensor, or communication fault	Diagnose ESC system and related sensors
43	Brake Light Switch Fault	Brake lights/regen behavior abnormal	Switch or wiring failure	Test and replace switch if required
44	Brake Light Does Not Operate	Rear brake lights remain OFF	Fuse, switch, wiring, or lamp fault	Check complete brake-light circuit
45	Brake Light Stays ON	Brake lights remain illuminated	Stuck switch or incorrect adjustment	Inspect and adjust/replace switch
46	Regenerative Braking Noise	Whining/whirring during deceleration	Motor-generator or inverter operation/fault	Identify normal operating noise versus abnormal noise; scan if necessary
47	Regenerative Braking Jerking	Uneven deceleration	Poor brake blending, sensor or control issue	Check pedal sensors, brake ECU, and motor torque control
48	Brake Warning With Low HV Battery	Regeneration unavailable	Battery SOC/temperature limitation or HV fault	Check battery status and hybrid DTCs
49	Regeneration Limited With Full Battery	Reduced regenerative braking	Battery cannot accept additional charge	System normally increases friction braking; verify if behavior is abnormal
50	Brake System Emergency/Limp Mode	Warning lights and reduced braking assistance	Major ABS, actuator, booster, HV or communication fault	Stop safely, scan all relevant ECUs andthe manufacturer’sfacturer emergency repair procedure
No.	Brake System Problem	Common Symptoms	Possible Causes	Solution / Repair
51	Brake Actuator Pump Runs Continuously	Pump noise remains ON frequently	Pressure loss, internal leakage, or actuator fault	Check hydraulic pressure and actuator for leakage
52	Brake Actuator Pump Does Not Run	Hard pedal, brake warning	Pump motor, fuse, relay or ECU fault	Check power, ground, fuse, and actuator motor
53	Brake Actuator Pressure Sensor Fault	ABS/brake warning	Sensor or wiring fault	Check sensor signal and wiring
54	Brake Pressure Sensor Calibration Error	Incorrect brake pressure data	Lost calibration or sensor replacement	Perform manufacturer-specified calibration
55	Brake Pressure Sensor Signal Intermittent	Brake warning appears intermittently	Loose connector or damaged wiring	Inspect connector, wiring, and sensor
56	Brake Hydraulic Line Restriction	Uneven braking	Damaged/collapsed brake hose or pipe	Inspect and replace restricted line
57	Brake Hose Internally Collapsed	One brake remains partially applied	Internal hose deterioration	Replace affected brake hose
58	Brake Fluid Air Contamination	Spongy pedal	Air introduced during service	Bleed hydraulic system using specified procedure
59	Incorrect Brake Fluid Type	Seal/brake-system problems	Incorrect fluid used	Flush system and use manufacturer-specified fluid
60	Brake Fluid Reservoir Level Sensor Fault	Brake warning with normal fluid level	Sensor or wiring fault	Test sensor and circuit
61	Brake Fluid Level Low	Brake warning, long pedal	Leakage or worn pads	Inspect for leakage and brake-pad condition
62	Brake Fluid Reservoir Cap Fault	Fluid contamination/moisture	Damaged cap seal	Replace reservoir cap if required
63	Brake Caliper Piston Seized	Brake drag and overheating	Corrosion or contamination	Service or replace caliper
64	Brake Caliper Slider Pin Seized	Uneven pad wear	Corrosion/lack of lubrication	Clean/service or replace slider components
65	Uneven Brake Pad Wear	One pad wears faster	Sticking caliper or slider	Diagnose caliper and hydraulic system
66	Brake Pad Sensor Fault	Brake-service warning	Damaged wear sensor/wiring	Inspect and replace sensor if equipped
67	Brake Pad Wear Excessive	Grinding/noise	Pad wear, caliper drag, or driving conditions	Inspect and replace pads as necessary
68	Brake Disc Thickness Below Limit	Poor braking/possible vibration	Excessive wear	Measure disc thickness and replace if below specification
69	Brake Disc Hot Spots	Vibration/noise	Repeated heavy braking or brake drag	Inspect disc and caliper; replace if necessary
70	Brake Disc Surface Rust	Noise during initial braking	Vehicle parked for extended period	Perform controlled brake operation; inspect if persistent
71	Parking Brake Not Releasing	Vehicle difficult to move	EPB actuator, switch or mechanical fault	Diagnose EPB system and release mechanism
72	Electronic Parking Brake Fault	EPB warning	EPB actuator, ECU or wiring fault	Scan EPB system and repair
73	Electronic Parking Brake Motor Stuck	Parking brake remains applied	Actuator failure or corrosion	Diagnose and replace actuator if required
74	Auto-Hold Function Not Working	Vehicle rolls at stops	ABS/ESC, brake switch or sensor fault	Scan system and verify required conditions
75	Auto-Hold Releases Unexpectedly	Vehicle moves when expected to remain stopped	Sensor/control fault or system condition	Check brake control ECU and related sensors
76	Hill-Hold Assist Not Working	Vehicle rolls backward on incline	ABS/ESC or brake-control fault	Diagnose stability-control system
77	Hill-Start Brake Control Fault	Warning on dashboard	Brake ECU, yaw sensor or wheel-speed fault	Scan and calibrate relevant sensors
78	Brake Assist Function Fault	Increased stopping distance	Booster or control-system fault	Test brake-assist system
79	Emergency Brake Assist Not Available	Driver-assistance warning	Camera/radar/ESC or brake ECU fault	Diagnose ADAS and braking system
80	Automatic Emergency Braking Fault	AEB warning/disabling	Radar, camera, calibration or communication issue	Scan ADAS system and perform calibration
81	Front Radar Brake Function Fault	AEB/ACC unavailable	Radar blockage or misalignment	Clean, inspect and calibrate radar
82	Forward Camera Calibration Fault	AEB/ADAS warning	Camera misalignment or windshield replacement	Perform manufacturer-approved camera calibration
83	Adaptive Cruise Control Braking Fault	ACC unavailable	Radar, brake ECU or communication fault	Diagnose ACC and brake-control network
84	Collision Warning System Fault	Safety warning	Radar/camera/sensor fault	Check ADAS sensors and calibration
85	Brake-by-Wire Communication Fault	Brake warning/reduced functions	CAN/Ethernet communication issue	Diagnose network and affected modules
86	Brake-by-Wire Control Module Fault	Abnormal brake response	ECU hardware/software fault	Scan module and follow manufacturer repair procedure
87	Brake Pedal Feel Inconsistent	Pedal feel changes between stops	Brake blending, actuator or software issue	Check brake-control system and calibration
88	Regenerative-to-Friction Transition Harsh	Noticeable braking change	Incorrect blending/calibration or sensor problem	Check pedal sensors, HCU and brake ECU
89	Regenerative Braking Too Aggressive	Vehicle slows sharply after accelerator release	Control calibration or drive-mode setting	Check system settings and control calibration
90	Regenerative Braking Too Weak	Poor deceleration on accelerator release	Battery limitation or control fault	Check SOC, temperature,rature and motor torque command
91	Regenerative Braking Disabled by ABS Fault	No energy recovery	ABS/ESC system fault	Repair ABS/ESC fault and recheck regeneration
92	Regeneration Limited During Cold Operation	Reduced regenerative braking	Cold HV battery	Allow system to reach operating temperature; diagnose if excessive
93	Regeneration Limited During High Battery Temperature	Reduced energy recovery	HV battery thermal protection	Check battery cooling system
94	Regeneration Limited at High Battery SOC	Less regenerative braking	Battery nearly/full charged	Normal system behavior; friction braking supplements regeneration
95	Motor Regenerative Torque Sensor Fault	Inconsistent deceleration	Motor position/current feedback fault	Diagnose motor/inverter feedback system
96	Inverter Regenerative Control Fault	Regeneration unavailable	Inverter control or power-module fault	Scan inverter and inspect cooling/power circuits
97	HV Battery Cannot Accept Regenerative Energy	Battery SOC does not increase normally	Battery fault, temperature or charge limitation	Check BMS, battery temperature, and cell condition
98	Brake ECU Software/Calibration Error	Unusual braking behavior	Incorrect software/calibration	Verify software version and perform approved programming/calibration
99	Multiple ABS/ESC/HV Warning Lights	Several warning lamps illuminate	Common power, ground or communication fault	Scan all ECUs and diagnose shared circuits
100	Hybrid Brake System Completely Disabled	Major warning, limited braking assistance	Serious actuator, ECU, HV or hydraulic fault	Stop safely, follow manufacturer emergency procedure, and perform complete diagnosis

Advanced HEV Brake Diagnostic Flow

Safety: HEV brake systems may combine high-voltage components with electronically controlled hydraulic braking. Follow the manufacturer’s HV isolation, brake bleeding, calibration, and diagnostic procedures, and use the required PPE and approved equipment.