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. | 🟡 Soon |
| P3000 | HV Battery Malfunction | General hybrid battery system fault. Check individual module voltages with Dr. Prius app. | 🟡 Soon |
| P3006 | HV Battery Module Voltage Variation | One module is significantly weaker than others — common sign of aging battery needing reconditioning. | 🟡 Soon |
| P3009 | HV Battery Leak Detected | Insulation failure in HV system. Could be wiring, battery casing, or inverter. Get this diagnosed professionally. | 🔴 Immediate |
| P0A0F | Drive Motor "A" Position Sensor Circuit | Resolver issue or wiring fault in MG2 (traction motor). Check wiring harness first. | 🟡 Soon |
| P0A93 | Inverter Cooling System Performance | Inverter coolant pump failing or failed. Replace immediately. | 🔴 Immediate |
| P0A94 | DC/DC Converter Performance | DC-DC converter (charges 12V from HV battery) is underperforming. Often precedes 12V battery failure. | 🟡 Soon |
Brake & ABS System Codes (Cxxxx)
| Code | Description | Common Cause | Urgency |
|---|---|---|---|
| C1210 | Brake Actuator Malfunction | ABS actuator pump failing. You'll see ABS, VSC, and brake lights together. See ABS guide. | 🔴 Immediate |
| 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 |
| 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. | 🟢 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. | 🟡 Soon |
| P0420 | Catalyst System Efficiency Below Threshold | Catalytic converter degraded. O2 sensor could also be the culprit. Test sensor first before replacing cat. | 🟡 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 |
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.
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.