Red triangle on dash? This is your car's "master warning" light. It means at least one hybrid system fault is active. Do NOT ignore it — read the code immediately with an OBD2 scanner before driving further. See Tools & Parts for scanner recommendations.
Hybrid System Codes (P3xxx / Px0A)
| Code | Description | Common Cause | Urgency |
|---|---|---|---|
| P0A80 | Replace Hybrid Battery Pack | One or more battery modules has degraded significantly. May recondition or need replacement. See Hybrid Battery guide. | 🟡 Soon |
| P3000 | HV Battery Malfunction | General hybrid battery system fault. Check individual block voltages with Dr. Prius app (14 blocks, each = 2 modules). See Hybrid Battery guide. | 🟡 Soon |
| P3006 | HV Battery Module Voltage Variation | One module is significantly weaker than others — common sign of aging battery needing reconditioning. See Hybrid Battery guide. | 🟡 Soon |
| P3009 | HV Battery Leak Detected | Insulation failure in HV system. Could be wiring, battery casing, or inverter. Get this diagnosed professionally. See Hybrid Battery guide for HV system context. | 🔴 Immediate |
| P0A0F | Engine Failed to Start | The HV system tried to start the ICE engine and it didn't start within the timeout. Most common cause: throttle body carbon buildup (especially after a 12V battery replacement — the ECU loses its learned throttle position). Also: weak 12V battery (see 12V Battery guide), dirty MAF sensor, fuel delivery failure, ignition coil fault (see Spark Plug guide). Red triangle; car will not move or goes into limp mode. | 🔴 Immediate |
| P0A93 | Inverter Cooling System Performance | Inverter coolant pump failing or failed. Replace immediately. See Inverter Pump guide. | 🔴 Immediate |
| P0A94 | DC/DC Converter Performance | DC-DC converter (charges 12V from HV battery) is underperforming. Often precedes 12V battery failure. See 12V Battery guide. | 🟡 Soon |
| P3004 | Power Cable Fault | Fault detected in the HV power cable between the battery pack and the inverter. Could be insulation failure, a loose connection at the inverter or battery side, or internal cable damage. Do not drive — this is a high-voltage system fault. Have it diagnosed before continuing. | 🔴 Immediate |
Brake & ABS System Codes (Cxxxx)
| Code | Description | Common Cause | Urgency |
|---|---|---|---|
| C1252 | Brake Booster Pump Motor ON Time Abnormally Long | Brake booster pump motor failing — the primary code for "3 amigos." Pump runs continuously and drains 12V battery. See ABS actuator guide. | 🔴 Immediate |
| C1253 | Brake Booster Pump Motor Relay Malfunction | Brake booster pump relay fault. Appears alongside C1252. Confirms actuator assembly failure. See ABS actuator guide. | 🔴 Immediate |
| C1241 | Low Battery Positive Voltage | 12V auxiliary battery voltage is too low for the brake control system to operate normally. This is a 12V battery problem, not an ABS actuator problem — check and charge the 12V battery before assuming brake actuator failure. Often appears with C1336 but without C1252/C1253. See 12V Battery guide. | 🟡 Soon |
| C1210 | Zero Point Calibration of Yaw Rate Sensor Undone | Yaw rate sensor calibration lost — often after a battery disconnect or ECU reset. Commonly appears alongside C1252/C1253 but is NOT the cause of actuator failure. Usually self-corrects after driving straight on a level road. See ABS actuator guide. | 🟢 Low |
| C0200 | ABS Wheel Speed Sensor — Front Right | Sensor or wiring fault. Common after suspension work. Check wiring harness at the wheel. | 🟡 Soon |
| C0205 | ABS Wheel Speed Sensor — Front Left | Same as above, opposite side. | 🟡 Soon |
| C0210 | ABS Wheel Speed Sensor — Rear Right | Rear sensors are often damaged by rust or road debris. Inspect sensor and tone ring. | 🟡 Soon |
| C0215 | ABS Wheel Speed Sensor — Rear Left | Same as C0210, opposite side. | 🟡 Soon |
| C1336 | Zero Point Calibration of Deceleration Sensor Undone | After battery disconnect or skid control ECU reset, the sensor needs recalibration. Drive in a straight line on flat road to reset. See ABS actuator guide. | 🟢 Low |
Engine Codes (P0xxx)
| Code | Description | Common Cause | Urgency |
|---|---|---|---|
| P0301–P0304 | Misfire — Cylinders 1–4 | Spark plugs, ignition coils, or injectors. Check plugs first — they're often overdue. See Spark Plug guide. | 🟡 Soon |
| P0420 | Catalyst System Efficiency Below Threshold | Catalytic converter degraded. O2 sensor could also be the culprit — test sensor live data before replacing the cat. No drivability impact. See P0420 guide. | 🟡 Monitor |
| P0441 | Evaporative Emission Control System Incorrect Purge Flow | Often a loose or bad gas cap. Tighten cap and clear code — if it returns, check EVAP lines. | 🟢 Low |
| P0171 | System Too Lean (Bank 1) | MAF sensor dirty or failing, vacuum leak, or low fuel pressure. Clean MAF sensor first. | 🟡 Soon |
| P1121 | Coolant Flow Control Valve Position Sensor Signal Malfunction | The three-way coolant valve is stuck or its position sensor has failed. Symptoms: no cabin heat, longer cold-start warm-up, slight fuel economy loss. Toyota-specific code. See P1121 guide. | 🟡 Soon |
Understanding the Warning Lights
Red Triangle (Master Warning)
Hybrid system fault. Read codes immediately. Could be anything from inverter pump to hybrid battery to minor sensor issue. Do not ignore.
HV Battery Warning
Hybrid battery is failing or has a cell issue. Run Dr. Prius battery test and read codes. May be reconditionable.
ABS + VSC + Brake Lights (3 at once)
The "3 amigos" on a Gen 2. Almost always the ABS actuator assembly. See the ABS actuator guide.
Thermometer Warning
Engine overheating. Pull over immediately. On a Prius this could indicate head gasket issues at high mileage. Let engine cool fully before checking coolant level.
Check Engine Light (amber)
An emissions or engine management fault — P0xxx or P1xxx codes. On a Gen 2 the most common are P0420 (cat), P0171 (lean), or P0301–P0304 (misfire). Amber means read the code — not necessarily stop driving.
Always clear codes after repair and drive a full trip cycle before assuming the repair worked. Some codes require the car to complete specific drive conditions before confirming a fix. If the same code returns within a day of driving, the root cause is still present.