2017 Toyota Mirai Won't Start, No Click or Crank Diagnosis

Car Won't Start, No Click or Crank 2017 Toyota Mirai

Experiencing a completely silent start attempt in your 2017 Toyota Mirai can be unsettling. When you press the power button and get no response – no dashboard lights, no "Ready" indicator, no whirring sounds, and certainly no "crank" (as a fuel cell vehicle doesn't have one in the traditional sense) – it points to a critical power delivery issue. This guide will walk you through diagnosing why your Mirai might be refusing to power on, focusing on the most common culprits for a complete lack of response.

What drivers notice on this 2017 Toyota Mirai

When your 2017 Toyota Mirai fails to start with no accompanying sounds or dashboard activity, the primary observation is a complete lack of engagement from the vehicle's systems. You might notice:

• The "Ready" indicator light on the dashboard does not illuminate.
• The infotainment screen remains blank.
• No accessory power (radio, windows, lights) when the power button is pressed.
• The key fob may or may not unlock the doors, depending on the severity of the power loss.
• A general feeling of the vehicle being completely "dead."

At a glance: difficulty, repair cost, and diagnostic workflow

• Difficulty Rating: 6/10 — Moderate
• Common Symptoms: Dim or flickering dashboard lights: If any lights come on at all, they might be very weak.; Slow or unresponsive accessories: Prior to a full no-start, you might have noticed the radio cutting out or windows roll; Remote key fob issues: The fob might have struggled to lock/unlock doors, indicating a weak fob battery or a vehicle pow; No sounds from the vehicle: Unlike gasoline cars that might click or crank weakly, a Mirai in this state will typically
• Estimated Repair Cost: $100–$900 (parts + typical shop labor)
• OEM Tooling Required: Standard OBD-II scanner and hand tools

Diagnostic workflow:

1. Confirm the symptom on your vehicle.
2. Scan for stored or pending codes with an OBD-II tool.
3. Inspect the most common causes in this guide (visual checks first).
4. Run verification tests before replacing parts.
5. Repair, clear codes, and verify on a test drive.

Symptoms and warning signs

Beyond the primary symptom of a no-start, no-click, no-crank condition, other subtle signs might precede or accompany the issue:

• Dim or flickering dashboard lights: If any lights come on at all, they might be very weak.
• Slow or unresponsive accessories: Prior to a full no-start, you might have noticed the radio cutting out or windows rolling up slowly.
• Remote key fob issues: The fob might have struggled to lock/unlock doors, indicating a weak fob battery or a vehicle power issue.
• No sounds from the vehicle: Unlike gasoline cars that might click or crank weakly, a Mirai in this state will typically be completely silent.
• Error messages on the multi-information display: If the system has just enough power to partially boot, it might show warnings related to the 12V battery or hybrid system.

How to verify and confirm the issue

To accurately diagnose why your 2017 Toyota Mirai won't start with no response, you'll need to perform a few practical checks:

• Check the 12V Auxiliary Battery: Despite being a fuel cell vehicle, the Mirai relies on a conventional 12V battery to power its control systems, computers, and relays that initiate the fuel cell stack. This is the single most common cause of a no-start, no-click condition. Use a multimeter to check its voltage. A healthy battery should read around 12.6 volts. Anything below 12V indicates a discharged or failing battery.
• Test the Key Fob: A dead key fob battery can prevent the car from recognizing your attempt to start it. Try using a spare key fob if you have one, or replace the battery in your primary fob. Ensure the fob is physically close to the power button when attempting to start.
• Inspect Fuses: Check the main fuses in the under-hood fuse box and potentially the interior fuse box. Look for any blown fuses that supply power to the ignition system or main relays. Consult your owner's manual for fuse box locations and diagrams.
• Attempt a Jump Start: If you suspect the 12V battery, try jump-starting the vehicle. The Mirai has specific jump-start terminals, usually under the hood, not directly on the battery itself. Follow the procedure in your owner's manual carefully. If the car powers on after a jump, the 12V battery is almost certainly the culprit.
• Scan for Diagnostic Trouble Codes (DTCs): Even if the car doesn't fully start, a low 12V battery or other electrical faults can trigger DTCs in various control modules. A compatible OBD-II scanner can reveal these codes, providing clues to the underlying problem.

What is different on this year and model

It's crucial to understand that the 2017 Toyota Mirai is a Fuel Cell Electric Vehicle (FCEV), which operates differently from traditional gasoline cars or even conventional battery electric vehicles (BEVs). When we talk about a Mirai "starting," we're referring to the process of the vehicle's control systems engaging the fuel cell stack and electric drive components to enter "Ready" mode. Key differences include:

• No traditional starter motor: There's no internal combustion engine to crank. The vehicle uses an electric motor for propulsion.
• Critical 12V battery role: While the main propulsion comes from the fuel cell and high-voltage battery, the small 12V auxiliary battery is absolutely essential for powering the computers, relays, and contactors that bring the entire system online. Without a healthy 12V battery, the high-voltage system cannot be initialized.
• Fuel Cell System Complexity: Diagnosis can be more complex if the issue lies within the high-voltage or fuel cell system, requiring specialized tools and training.

Common causes (most likely first)

When your 2017 Toyota Mirai won't start with no click or crank, these are the most common reasons:

• Dead or Weak 12V Auxiliary Battery: This is by far the most frequent cause. The 12V battery powers all the vehicle's control modules and relays. If it's too weak, it can't energize the necessary components to bring the fuel cell system online.
• Faulty Key Fob or Dead Key Fob Battery: The vehicle needs to recognize the key fob to allow starting. A dead fob battery or a malfunctioning fob will prevent this.
• Blown Main Fuse or Relay: A critical fuse (e.g., main fuse, ignition system fuse, or a fuse related to the power control unit) can interrupt power flow. Similarly, a faulty main power relay can prevent the system from energizing.
• Bad Ignition Switch/Power Button: While less common, the physical power button or its internal contacts can fail, preventing the signal from reaching the vehicle's computers.
• Wiring Issues: Damaged or corroded wiring in the starting circuit can interrupt power or signals.
• Power Control Unit (PCU) Malfunction: The PCU manages the flow of power between the fuel cell, high-voltage battery, and electric motor. A fault here could prevent the system from entering "Ready" mode.
• Fuel Cell System Fault: In rare cases, a severe fault within the fuel cell stack or its associated components could prevent system initialization, although this often triggers specific warning lights if the system has enough power to partially boot.

Related guides on this vehicle

• Car Won't Start, No Click, No Crank 2017 Toyota Rav4 Diagnosis
• 2020 Toyota Highlander: Car Won't Start, No Crank, No Power At All
• 2017 Toyota Tundra Won't Start, Security Light Flashing

Step-by-step diagnosis and fixes

Follow these steps to diagnose and potentially resolve the no-start issue in your 2017 Toyota Mirai:

1. Check 12V Battery Voltage: Use a multimeter to measure the voltage across the 12V battery terminals (or jump-start terminals). If it's below 12.0V, charge or replace the battery. For detailed guidance on battery checks, refer to general All repair guides.
2. Inspect Key Fob: Replace the key fob battery. If the issue persists, try placing the fob directly against the power button when attempting to start. If you have a second fob, try that one.
3. Check Fuses: Locate the main fuse boxes (under the hood and possibly inside the cabin). Visually inspect any fuses related to the ignition, power control, or main vehicle systems. Replace any blown fuses with one of the correct amperage.
4. Attempt a Jump Start (12V System): Connect jumper cables to the designated jump-start terminals (refer to your owner's manual). If the Mirai powers on and enters "Ready" mode, the 12V battery is confirmed as the problem. Drive it to a service center or replace the battery.
5. Scan for Codes: If the vehicle still doesn't respond after the above steps, and if you can get enough power to the OBD-II port, connect a scan tool. Even a low-power condition can log codes in modules like the Body Control Module (BCM) or Power Management Control Unit.
6. Inspect Wiring and Connections: Look for any loose, corroded, or damaged wiring connections, especially around the 12V battery, fuse boxes, and the power button assembly.

Repair options and cost factors

The repair options and associated costs for a 2017 Toyota Mirai that won't start with no click or crank largely depend on the identified cause:

• 12V Auxiliary Battery Replacement: This is often the most straightforward and least expensive repair. Costs will vary based on battery type and labor.
• Key Fob Battery Replacement: A very inexpensive DIY fix.
• Key Fob Replacement/Reprogramming: If the fob itself is faulty, a new one will need to be purchased and programmed by a Toyota dealership.
• Fuse Replacement: A very low-cost repair, often DIY.
• Ignition Switch/Power Button Replacement: This repair involves replacing the power button assembly, which can be more involved and costly due to labor.
• Relay Replacement: Replacing a faulty main power relay is usually a moderate cost, combining parts and labor.
• Professional Electrical Diagnosis: If the issue is complex (e.g., wiring harness, PCU, or fuel cell system), professional diagnosis will be necessary. These repairs can range from moderate to significant, especially if high-voltage components or fuel cell stack components are involved. For more information on common vehicle issues, you can browse our vehicle-specific articles.

When to see a professional

While many 12V battery and key fob issues can be resolved by a DIY owner, there are clear instances when professional assistance is necessary for your 2017 Toyota Mirai:

• After basic checks fail: If you've checked the 12V battery, key fob, and fuses, and the car still won't respond.
• Suspected high-voltage system issues: Any indication of problems with the main high-voltage battery, fuel cell stack, or power control unit should immediately be handled by a certified Toyota technician trained in FCEV systems. These systems carry significant electrical hazards.
• Intermittent or complex electrical problems: If the issue is not consistent or seems to involve multiple systems, a professional can use advanced diagnostic tools to pinpoint the root cause.
• No access to diagnostic tools: If you don't have a multimeter or OBD-II scanner, a professional can quickly perform these checks.

Frequently asked questions

Why does my Mirai have a 12V battery if it's a fuel cell car?

The 12V auxiliary battery in your 2017 Toyota Mirai is crucial for powering all the low-voltage electronics, control modules, lights, infotainment system, and the relays that "boot up" the high-voltage fuel cell system. Without a healthy 12V supply, the vehicle's computers cannot initiate the complex sequence required to bring the fuel cell stack and electric motor online, leading to a no-start condition.

Can I jump-start a 2017 Toyota Mirai?

Yes, you can jump-start the 12V auxiliary battery in a 2017 Toyota Mirai. However, it's important to use the designated jump-start terminals, which are typically located under the hood, and not directly on the battery itself. Always refer to your owner's manual for the correct procedure to avoid damaging the vehicle's sensitive electronics.

What are signs of a failing 12V battery in a Mirai?

Signs of a failing 12V battery in a Mirai can include dimming interior or exterior lights, sluggish accessory operation (like power windows), intermittent dashboard warnings, or the car struggling to enter "Ready" mode. In severe cases, it will lead to a complete no-start, no-click, no-crank scenario as described in this article.

Sources and further reading

• Toyota Mirai Owner's Manual (2017 Edition)
• All repair guides
• Browse vehicles

This information is for general guidance only and is not a substitute for OEM service procedures; always use a qualified technician for safety-critical work.

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