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  <meta name="description" content="Common OBD2 and hybrid-specific error codes for the Gen 2 Toyota Prius (2004–2009). What the red triangle actually means.">
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  <h1>Error Codes</h1>
  <p>What the red triangle actually means — and what to do about it.</p>
</div>

<main>

  <section>
    <div class="notice danger">
      <strong>Red triangle on dash?</strong> 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 <a href="/tools" style="color:inherit;text-decoration:underline">Tools &amp; Parts</a> for scanner recommendations.
    </div>
  </section>

  <section>
    <h2>Hybrid System Codes (P3xxx / Px0A)</h2>
    <div class="table-wrap">
      <table>
        <thead>
          <tr><th>Code</th><th>Description</th><th>Common Cause</th><th>Urgency</th></tr>
        </thead>
        <tbody>
          <tr>
            <td><strong>P0A80</strong></td>
            <td>Replace Hybrid Battery Pack</td>
            <td>One or more battery modules has degraded significantly. May recondition or need replacement. See <a href="/repairs/hybrid-battery">Hybrid Battery guide</a>.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>P3000</strong></td>
            <td>HV Battery Malfunction</td>
            <td>General hybrid battery system fault. Check individual block voltages with Dr. Prius app (14 blocks, each = 2 modules). See <a href="/repairs/hybrid-battery">Hybrid Battery guide</a>.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>P3006</strong></td>
            <td>HV Battery Module Voltage Variation</td>
            <td>One module is significantly weaker than others — common sign of aging battery needing reconditioning. See <a href="/repairs/hybrid-battery">Hybrid Battery guide</a>.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>P3009</strong></td>
            <td>HV Battery Leak Detected</td>
            <td>Insulation failure in HV system. Could be wiring, battery casing, or inverter. Get this diagnosed professionally. See <a href="/repairs/hybrid-battery">Hybrid Battery guide</a> for HV system context.</td>
            <td>🔴 Immediate</td>
          </tr>
          <tr>
            <td><strong>P0A0F</strong></td>
            <td>Engine Failed to Start</td>
            <td>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 <a href="/repairs/12v-battery">12V Battery guide</a>), dirty MAF sensor, fuel delivery failure, ignition coil fault (see <a href="/repairs/spark-plugs">Spark Plug guide</a>). Red triangle; car will not move or goes into limp mode.</td>
            <td>🔴 Immediate</td>
          </tr>
          <tr>
            <td><strong>P0A93</strong></td>
            <td>Inverter Cooling System Performance</td>
            <td>Inverter coolant pump failing or failed. Replace immediately. See <a href="/repairs/inverter-pump">Inverter Pump guide</a>.</td>
            <td>🔴 Immediate</td>
          </tr>
          <tr>
            <td><strong>P0A94</strong></td>
            <td>DC/DC Converter Performance</td>
            <td>DC-DC converter (charges 12V from HV battery) is underperforming. Often precedes 12V battery failure. See <a href="/repairs/12v-battery">12V Battery guide</a>.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>P3004</strong></td>
            <td>Power Cable Fault</td>
            <td>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.</td>
            <td>🔴 Immediate</td>
          </tr>
        </tbody>
      </table>
    </div>
  </section>

  <section>
    <h2>Brake &amp; ABS System Codes (Cxxxx)</h2>
    <div class="table-wrap">
      <table>
        <thead>
          <tr><th>Code</th><th>Description</th><th>Common Cause</th><th>Urgency</th></tr>
        </thead>
        <tbody>
          <tr>
            <td><strong>C1252</strong></td>
            <td>Brake Booster Pump Motor ON Time Abnormally Long</td>
            <td>Brake booster pump motor failing — the primary code for "3 amigos." Pump runs continuously and drains 12V battery. See <a href="/repairs/abs-actuator">ABS actuator guide</a>.</td>
            <td>🔴 Immediate</td>
          </tr>
          <tr>
            <td><strong>C1253</strong></td>
            <td>Brake Booster Pump Motor Relay Malfunction</td>
            <td>Brake booster pump relay fault. Appears alongside C1252. Confirms actuator assembly failure. See <a href="/repairs/abs-actuator">ABS actuator guide</a>.</td>
            <td>🔴 Immediate</td>
          </tr>
          <tr>
            <td><strong>C1241</strong></td>
            <td>Low Battery Positive Voltage</td>
            <td>12V auxiliary battery voltage is too low for the brake control system to operate normally. This is a <strong>12V battery problem, not an ABS actuator problem</strong> — check and charge the 12V battery before assuming brake actuator failure. Often appears with C1336 but without C1252/C1253. See <a href="/repairs/12v-battery">12V Battery guide</a>.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>C1210</strong></td>
            <td>Zero Point Calibration of Yaw Rate Sensor Undone</td>
            <td>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 <a href="/repairs/abs-actuator">ABS actuator guide</a>.</td>
            <td>🟢 Low</td>
          </tr>
          <tr>
            <td><strong>C0200</strong></td>
            <td>ABS Wheel Speed Sensor — Front Right</td>
            <td>Sensor or wiring fault. Common after suspension work. Check wiring harness at the wheel.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>C0205</strong></td>
            <td>ABS Wheel Speed Sensor — Front Left</td>
            <td>Same as above, opposite side.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>C0210</strong></td>
            <td>ABS Wheel Speed Sensor — Rear Right</td>
            <td>Rear sensors are often damaged by rust or road debris. Inspect sensor and tone ring.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>C0215</strong></td>
            <td>ABS Wheel Speed Sensor — Rear Left</td>
            <td>Same as C0210, opposite side.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>C1336</strong></td>
            <td>Zero Point Calibration of Deceleration Sensor Undone</td>
            <td>After battery disconnect or skid control ECU reset, the sensor needs recalibration. Drive in a straight line on flat road to reset. See <a href="/repairs/abs-actuator">ABS actuator guide</a>.</td>
            <td>🟢 Low</td>
          </tr>
        </tbody>
      </table>
    </div>
  </section>

  <section>
    <h2>Engine Codes (P0xxx)</h2>
    <div class="table-wrap">
      <table>
        <thead>
          <tr><th>Code</th><th>Description</th><th>Common Cause</th><th>Urgency</th></tr>
        </thead>
        <tbody>
          <tr>
            <td><strong>P0301–P0304</strong></td>
            <td>Misfire — Cylinders 1–4</td>
            <td>Spark plugs, ignition coils, or injectors. Check plugs first — they're often overdue. See <a href="/repairs/spark-plugs">Spark Plug guide</a>.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>P0420</strong></td>
            <td>Catalyst System Efficiency Below Threshold</td>
            <td>Catalytic converter degraded. O2 sensor could also be the culprit — test sensor live data before replacing the cat. No drivability impact. See <a href="/repairs/p0420">P0420 guide</a>.</td>
            <td>🟡 Monitor</td>
          </tr>
          <tr>
            <td><strong>P0441</strong></td>
            <td>Evaporative Emission Control System Incorrect Purge Flow</td>
            <td>Often a loose or bad gas cap. Tighten cap and clear code — if it returns, check EVAP lines.</td>
            <td>🟢 Low</td>
          </tr>
          <tr>
            <td><strong>P0171</strong></td>
            <td>System Too Lean (Bank 1)</td>
            <td>MAF sensor dirty or failing, vacuum leak, or low fuel pressure. Clean MAF sensor first.</td>
            <td>🟡 Soon</td>
          </tr>
          <tr>
            <td><strong>P1121</strong></td>
            <td>Coolant Flow Control Valve Position Sensor Signal Malfunction</td>
            <td>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 <a href="/repairs/p1121">P1121 guide</a>.</td>
            <td>🟡 Soon</td>
          </tr>
        </tbody>
      </table>
    </div>
  </section>

  <section>
    <h2>Understanding the Warning Lights</h2>
    <div class="cards">
      <div class="card">
        <div class="card-icon">🔺</div>
        <h3>Red Triangle (Master Warning)</h3>
        <p>Hybrid system fault. Read codes immediately. Could be anything from inverter pump to hybrid battery to minor sensor issue. Do not ignore.</p>
      </div>
      <div class="card">
        <div class="card-icon">⚡</div>
        <h3>HV Battery Warning</h3>
        <p>Hybrid battery is failing or has a cell issue. Run Dr. Prius battery test and read codes. May be reconditionable.</p>
      </div>
      <div class="card">
        <div class="card-icon">🛑</div>
        <h3>ABS + VSC + Brake Lights (3 at once)</h3>
        <p>The "3 amigos" on a Gen 2. Almost always the ABS actuator assembly. See the <a href="/repairs/abs-actuator">ABS actuator guide</a>.</p>
      </div>
      <div class="card">
        <div class="card-icon">🌡️</div>
        <h3>Thermometer Warning</h3>
        <p>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.</p>
      </div>
      <div class="card">
        <div class="card-icon">⚠️</div>
        <h3>Check Engine Light (amber)</h3>
        <p>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.</p>
      </div>
    </div>
  </section>

  <section>
    <div class="notice tip">
      <strong>Always clear codes after repair</strong> 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.
    </div>
  </section>

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