Symptom
Vehicle will not power on
Pressing start produces nothing, or the car never reaches its ready state. On a hybrid or electric vehicle this is rarely the traction battery, however tempting that conclusion is. Two ordinary explanations come first: the small 12 volt battery, which is what wakes the computers that connect the main pack — so a flat one leaves a fully charged car completely dead — and the high-voltage interlock, which deliberately isolates the pack whenever a connector or cover is not properly closed. Both are cheap. Neither is the pack.
Also described as: won't start, no ready light, car is dead, won't power up, nothing happens when I press start, won't go into ready, completely dead, خودرو اصلا برق ندارد, ماشین هیچ عکس العملی ندارد, no da contacto, no enciende nada, no responde boton arranque, coche sin corriente, لا يوجد كهرباء بالسيارة, الكونتاكت لا يفتح, ما في أي استجابة, ما تفتح ولا لمبة
Some causes mean you should stop driving
47 of the 117 codes that produce this symptom indicate a fault where continuing to drive risks damage or is unsafe. If the symptom is sudden or severe, treat it as one of those until a scan says otherwise.
What this usually means
On a hybrid or an electric car this is rarely the traction battery, and the instinct that it must be is what makes the fault expensive. The small 12 volt battery is what wakes the computers, and those computers are what close the contactors connecting the main pack. So a flat 12 volt battery leaves a fully charged car completely dead, and the diagnosis costs less than the tow.
Battery-test manufacturers put the majority of hybrid no-start cases at the 12 volt auxiliary, and the reason is structural rather than bad luck: it is often physically small, it is cycled harder than the battery in a conventional car because it supports the electronics rather than a starter motor, and nothing about the way the car drives warns that it is dying.
Its failure signature is distinctive and worth recognising. The dashboard lights up, the screens come on, and the car simply never reaches READY — there is enough energy to wake the system and not enough to pull in the high voltage relays. Rapid clicking as you press start is the same thing heard rather than seen. A cluster of unrelated warning lights arriving together — hybrid system, ABS, stability control, brake — is also a low-voltage signature rather than four faults, because every module browns out at once.
The second ordinary cause is the high voltage interlock, which isolates the pack deliberately whenever a service plug, connector or cover is not properly closed. It presents as a total refusal to power on and is a normal safety response rather than a failure — and it is the first thing to suspect if anything has recently been disconnected around the pack.
Do not test a hybrid's 12 volt battery on voltage alone. A battery reading 12.6 V can still collapse under load with a failed cell, and this is precisely the population where that happens — the load or conductance test is the one that decides.
Working through it
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Dash lights and screens come on, but READY never appears | 12 volt auxiliary battery too weak to close the high voltage contactors | Load or conductance test the 12 volt battery — voltage alone passes batteries that then collapse. Watch system voltage during a start attempt; a large sag confirms it. | Renew the 12 volt battery to the specified type, and register it where the car has energy management. |
| Rapid clicking from behind the dash or under the bonnet when start is pressed | Relays trying and failing to hold in on insufficient voltage — the same fault, heard rather than seen | Measure 12 volt system voltage during the attempt rather than at rest. Clicking is a current symptom, not a relay fault. | Charge or renew the 12 volt battery, then re-test. Do not renew relays on the sound. |
| Several unrelated warning lights arrive together, then nothing works | Low system voltage browning out every module at once, not four independent faults | Read the codes but do not chase them individually — check 12 volt supply and earths first. Codes set during a brown-out are consequences. | Restore the 12 volt supply, clear the codes, and re-scan. Only what returns is real. |
| Completely dead — no lights, no screens, no response | 12 volt battery flat or disconnected, a main fuse, or a lost earth | Voltage at the 12 volt battery posts, then at the main distribution point. Check the battery is where you think it is — many hybrids site it in the boot. | Charge or renew, remake connections, replace the fuse and find why it opened. |
| Will not power on since work was done near the high voltage system | High voltage interlock open — a service plug, connector or cover not properly closed | Read interlock circuit status on a scan tool. This is a designed safety response and it is doing its job, so look for what is not latched rather than for a failed part. | Close and latch the connector or cover properly. Only qualified high voltage work should go further than this. |
| 12 volt battery tests good and READY still does not come | The pack or its management genuinely refusing — isolation fault, contactor, or a stored fault inhibiting the start | Read hybrid or EV system codes and pack isolation status. Only reach this row after the 12 volt side is proven, because it is where the cost is. | High voltage diagnosis by a qualified technician. Do not open the pack without the training and the equipment. |
-
Dash lights and screens come on, but READY never appears
- Likely cause
- 12 volt auxiliary battery too weak to close the high voltage contactors
- How to confirm it
- Load or conductance test the 12 volt battery — voltage alone passes batteries that then collapse. Watch system voltage during a start attempt; a large sag confirms it.
- What fixes it
- Renew the 12 volt battery to the specified type, and register it where the car has energy management.
-
Rapid clicking from behind the dash or under the bonnet when start is pressed
- Likely cause
- Relays trying and failing to hold in on insufficient voltage — the same fault, heard rather than seen
- How to confirm it
- Measure 12 volt system voltage during the attempt rather than at rest. Clicking is a current symptom, not a relay fault.
- What fixes it
- Charge or renew the 12 volt battery, then re-test. Do not renew relays on the sound.
-
Several unrelated warning lights arrive together, then nothing works
- Likely cause
- Low system voltage browning out every module at once, not four independent faults
- How to confirm it
- Read the codes but do not chase them individually — check 12 volt supply and earths first. Codes set during a brown-out are consequences.
- What fixes it
- Restore the 12 volt supply, clear the codes, and re-scan. Only what returns is real.
-
Completely dead — no lights, no screens, no response
- Likely cause
- 12 volt battery flat or disconnected, a main fuse, or a lost earth
- How to confirm it
- Voltage at the 12 volt battery posts, then at the main distribution point. Check the battery is where you think it is — many hybrids site it in the boot.
- What fixes it
- Charge or renew, remake connections, replace the fuse and find why it opened.
-
Will not power on since work was done near the high voltage system
- Likely cause
- High voltage interlock open — a service plug, connector or cover not properly closed
- How to confirm it
- Read interlock circuit status on a scan tool. This is a designed safety response and it is doing its job, so look for what is not latched rather than for a failed part.
- What fixes it
- Close and latch the connector or cover properly. Only qualified high voltage work should go further than this.
-
12 volt battery tests good and READY still does not come
- Likely cause
- The pack or its management genuinely refusing — isolation fault, contactor, or a stored fault inhibiting the start
- How to confirm it
- Read hybrid or EV system codes and pack isolation status. Only reach this row after the 12 volt side is proven, because it is where the cost is.
- What fixes it
- High voltage diagnosis by a qualified technician. Do not open the pack without the training and the equipment.
Codes that produce this symptom (117)
Listed with the codes that most typically present this way first — the likeliest place to start.
- P0A0A High Voltage System Interlock Circuit A Typical of this code Stop driving Critical
- P0A0B High Voltage System Interlock Circuit A Performance Typical of this code Stop driving Critical
- P0A0C High Voltage System Interlock Circuit A Low Typical of this code Stop driving Critical
- P0A0D High Voltage System Interlock Circuit A High Typical of this code Stop driving Critical
- P0A0E High Voltage System Interlock Circuit A Intermittent Typical of this code Stop driving Critical
- P0A27 Hybrid/EV Battery Power Off Circuit Typical of this code High
- P0A28 Hybrid/EV Battery Power Off Circuit Low Typical of this code High
- P0A7D Hybrid/EV Battery Pack State of Charge Low Typical of this code Moderate
- P0A95 High Voltage Fuse A Typical of this code High
- P0AA0 Hybrid/EV Battery Positive Contactor Circuit Typical of this code High
- P0AA2 Hybrid/EV Battery Positive Contactor Circuit Stuck Open Typical of this code High
- P0AA3 Hybrid/EV Battery Negative Contactor Circuit Typical of this code High
- P0AA5 Hybrid/EV Battery Negative Contactor Circuit Stuck Open Typical of this code High
- P0AD9 Hybrid/EV Battery Positive Contactor Control Circuit/Open Typical of this code High
- P0ADD Hybrid/EV Battery Negative Contactor Control Circuit/Open Typical of this code High
- P0AE1 Hybrid/EV Battery Precharge Contactor Circuit Typical of this code High
- P0AE3 Hybrid/EV Battery Precharge Contactor Circuit Stuck Open Typical of this code High
- P0AE4 Hybrid/EV Battery Precharge Contactor A Control Circuit/Open Typical of this code High
- P0AFA Hybrid/EV Battery System Voltage Low Typical of this code High
- P0AFE Hybrid/EV Battery System Voltage Too Low for Voltage Step Up Conversion Typical of this code High
- P0AFF System Voltage Too Low for Voltage Step Down Conversion Typical of this code High
- P0B33 High Voltage Service Disconnect Circuit Typical of this code Stop driving High
- P0B34 High Voltage Service Disconnect Circuit Performance Typical of this code Stop driving High
- P0B35 High Voltage Service Disconnect Circuit Low Typical of this code Stop driving High
- P0B36 High Voltage Service Disconnect Circuit High Typical of this code Stop driving High
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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