Experiencing a car that won’t crank can be frustrating and disruptive. Before you call for professional help, understanding the potential causes and knowing how to diagnose them can save you time and money. This comprehensive guide provides a step-by-step Car Not Crank Diagnosis Chart to help you systematically troubleshoot the issue and get your vehicle back on the road. We’ll cover the most common culprits, from a dead battery to more complex electrical and fuel system problems.
Step 1: Is Your Car Cranking or Not? – The First Key Question
The very first step in our car not crank diagnosis chart is to clearly determine what happens when you turn the ignition key. This crucial initial observation will immediately direct your troubleshooting path.
- If your car cranks (the engine turns over but doesn’t start): This indicates the starter motor and battery are likely functioning. Skip ahead to Step 2: Cranks But Will Not Fire.
- If your car does not crank (no engine turning over, possibly no sound or just a click): This points to issues within the starting system itself. Continue with Step 1a: No Cranking – Starter and Related Systems.
Step 1a: No Cranking – Starter and Related Systems
If your car makes no attempt to crank, or you hear only a click or silence when turning the key to “START,” the problem likely lies within the starter system. Let’s systematically check the components:
1a.1: Battery Check
The battery is the most common cause of a car not cranking, especially if:
- The car has been sitting for an extended period.
- The weather is extremely cold.
- Your battery is old (typically 3-5 years lifespan).
Diagnosis & Action:
- Visual Inspection: Check the battery terminals for corrosion. Clean them with a wire brush and baking soda solution if necessary. Ensure the battery cables are tightly connected.
- Voltage Test: Use a multimeter to check the battery voltage. A healthy battery should read around 12.6 volts when the engine is off. A reading below 12 volts indicates a discharged or failing battery.
- Load Test: A voltage test alone isn’t definitive. A battery can show 12V but lack the current (amps) needed to crank the engine. The best way to test is with a load test, which you can often get done for free at auto parts stores. They have specialized testers that simulate engine cranking load.
- Jump Start: Try jump-starting your car using jumper cables and another vehicle. If the car starts with a jump, it strongly suggests a battery issue.
- Battery Replacement: If the battery fails a load test or jump-starting works, battery replacement is likely the solution.
1a.2: Ignition Switch Check
The ignition switch is an electrical switch that activates the starter and other circuits when you turn the key. A faulty ignition switch can prevent power from reaching the starter.
Diagnosis & Action:
- Turn Key and Listen: Turn the ignition key to the “START” position and listen carefully for any clicking sounds from the starter solenoid (usually located on the starter motor). If you hear a click, it could indicate the ignition switch is sending power, but the starter or solenoid itself might be the issue. Silence suggests the ignition switch might not be working.
- Ignition Switch Cleaning (DIY – Proceed with Caution): In some cases, dirty contacts within the ignition switch can cause problems. This is a more advanced step and should be done with caution and only if you are comfortable working on car electronics. Consult your vehicle’s repair manual for location and safe removal procedures. Carefully clean the electrical contacts with electrical contact cleaner.
- Professional Diagnosis: Testing the ignition switch thoroughly often requires a multimeter and understanding of your car’s wiring diagram. If cleaning doesn’t work or you are unsure, it’s best to have a qualified mechanic diagnose the ignition switch.
1a.3: Starter and Solenoid Check
The starter motor is responsible for physically turning the engine over. The solenoid is an electromagnetic switch that engages the starter motor with the engine’s flywheel and provides high current to the starter.
Diagnosis & Action:
- Check for Power at Starter: Using a multimeter, check for 12V power at the starter motor’s positive terminal when the ignition key is in the “START” position. Be extremely careful working around the starter and battery terminals, as these carry high current.
- Listen for Solenoid Click (Again): If you hear a distinct “click” from the starter area when turning the key to “START,” the solenoid is likely engaging. However, a clicking solenoid doesn’t guarantee the starter motor itself is functioning.
- Starter “Tap” Test (Caution): This is an old technique and should be done with caution and only if you are comfortable. Sometimes, a starter motor can get stuck. Have someone hold the ignition key in the “START” position (briefly – don’t overheat the starter), and gently tap the starter motor housing with a hammer or wrench. Avoid hitting electrical connections. If the car suddenly cranks after tapping, it might indicate a worn starter motor. This is not a reliable long-term fix and usually means the starter is failing.
- Professional Starter Test & Replacement: The most reliable way to test the starter and solenoid is to have them professionally tested. Mechanics have specialized equipment to bench-test starters. If the starter or solenoid is faulty, replacement is necessary.
Step 2: Cranks But Will Not Fire – Ignition, Fuel, and Timing
If your engine cranks (turns over) but doesn’t start and run, the issue is likely related to:
- Ignition System: Lack of spark to ignite the fuel-air mixture.
- Fuel System: Insufficient fuel reaching the engine cylinders.
- Engine Timing: Though less common for sudden no-start issues, incorrect timing can prevent starting.
2a: Check Engine Light (CEL) – Your First Clue
When you turn the key to the “RUN” position (before “START”), observe your dashboard.
- Does the Check Engine Light (CEL) illuminate?
- YES: This is a crucial indicator! The Engine Control Unit (ECU) is likely powered and has detected some fault. Proceed to 2a.1: Pull Diagnostic Trouble Codes (DTCs).
- NO: If the CEL does not light up in the “RUN” position, this suggests a more fundamental problem with ECU power or the ECU itself. Proceed to 2a.2: No Check Engine Light – ECU Power and Fuses.
2a.1: Pull Diagnostic Trouble Codes (DTCs)
A lit Check Engine Light means your car’s computer (ECU) has stored fault codes. These codes are invaluable for diagnosis.
Diagnosis & Action:
- OBD-II Scanner: Use an OBD-II scanner (you can buy one or borrow/rent from auto parts stores) to retrieve the stored Diagnostic Trouble Codes (DTCs).
- Record and Research Codes: Write down all the DTC codes. Consult a reliable DTC code database (online or in a repair manual) to understand what each code signifies. Codes often point to specific systems or sensors that are malfunctioning.
- Clear Codes (Optional but Recommended): After recording the codes, clear them using the scanner.
- Attempt to Start Again: Try starting the car again.
- Re-scan for Codes: If the car still doesn’t start, re-scan for DTCs. New codes that appear after attempting to start are often more relevant to the current no-start condition.
- Focus on Relevant Codes: Prioritize codes related to:
- Crankshaft Position Sensor (CKP) or Camshaft Position Sensor (CMP): Essential for ignition and fuel timing.
- Ignition System (Coils, Modules): Direct ignition problems.
- Fuel System (Fuel Pump, Injectors, Fuel Pressure): Fuel delivery issues.
2a.2: No Check Engine Light – ECU Power and Fuses
If the Check Engine Light doesn’t illuminate in the “RUN” position, the ECU may not be receiving power or is faulty.
Diagnosis & Action:
- Check Fuses: Locate the fuse box(es) in your car (usually under the dashboard and/or in the engine compartment). Consult your owner’s manual for fuse box diagrams.
- “ECU” or “PCM” Fuse: Look for fuses specifically labeled “ECU” (Engine Control Unit) or “PCM” (Powertrain Control Module).
- “Ignition” Fuse: Check fuses related to the ignition system.
- “Fuel Pump” Fuse: Check the fuel pump fuse.
- “Main Relay” or “EFI Main Relay” Fuse: Some cars have a main relay that powers up the ECU and other systems.
- Inspect and Test: Visually inspect each fuse for a broken filament. Use a fuse tester or multimeter to confirm continuity (that the fuse is not blown). Replace any blown fuses with the correct amperage rating.
- Check Relays: Relays are electrical switches that control higher current circuits. Faulty relays can prevent power from reaching the ECU or fuel pump.
- ECU Relay/Main Relay: Locate the relay that powers the ECU (refer to your repair manual).
- Fuel Pump Relay: Locate the fuel pump relay.
- Relay Swap Test: If you suspect a relay, try swapping it with an identical relay from a less critical system (e.g., horn relay – check your manual for compatible relays). If the car starts after swapping, the original relay is likely faulty.
- ECU Power Supply: If fuses and relays are good, but still no CEL, there might be a wiring issue preventing power from reaching the ECU, or the ECU itself could be faulty. This is a more advanced diagnosis step requiring wiring diagrams and potentially professional help.
2b: Ignition System Checks (Cranks But No Start)
If you have spark, your ignition system is likely functioning. If not, let’s investigate.
Diagnosis & Action:
- Spark Test: The most direct way to check for spark is to perform a spark test.
- Remove a Spark Plug: Carefully remove a spark plug from one of the cylinders.
- Re-attach to Coil/Wire: Reconnect the spark plug to its spark plug wire or ignition coil.
- Ground the Plug: Ground the threaded metal part of the spark plug to the engine block or chassis (use jumper cables or pliers with insulated handles if needed).
- Crank Engine and Observe: Have someone crank the engine while you observe the spark plug tip. Look for a bright blue or white spark jumping across the electrode gap.
- Repeat for Other Cylinders: Test spark on multiple cylinders to get a comprehensive picture.
- No Spark: If you have no spark on any cylinders, proceed to check ignition components.
- Spark Present: If you have good spark, skip to 2c: Fuel System Checks.
- Inspect Spark Plugs: While you have the spark plugs out, visually inspect them:
- Fouling: Are they excessively dirty, oily, or carbon-fouled?
- Wetness: Are they wet with fuel? (Wet plugs can indicate fuel delivery but also potential over-fueling).
- Damage: Check for cracked porcelain insulators or damaged electrodes.
- Ignition Coil Checks:
- Power to Coils: Use a multimeter to check for power (typically 12V) at the positive terminal of the ignition coil connectors when the ignition is in the “RUN” position. No power indicates a wiring or power supply issue (fuses, relays).
- Coil Resistance Test (Advanced): You can test the resistance of the ignition coils using a multimeter and comparing readings to manufacturer specifications (refer to a repair manual). This tests the internal windings of the coil.
2c: Fuel System Checks (Cranks But No Start)
If you have spark but still no start, the fuel system is the next area to investigate.
Diagnosis & Action:
- Listen for Fuel Pump: When you turn the ignition key to the “RUN” position (before “START”), listen carefully for the fuel pump to prime. You should hear a brief whirring or buzzing sound from the fuel tank area (often under the rear seat or towards the back of the car).
- Fuel Pump Sound: If you hear the pump prime, it suggests the pump is working, but doesn’t guarantee adequate fuel pressure.
- No Fuel Pump Sound: No sound could indicate a faulty fuel pump, fuel pump relay, fuse, or wiring issue.
- Fuel Pump Relay and Fuse (Re-check): Re-examine the fuel pump fuse and relay to ensure they are functioning (see 2a.2).
- Fuel Pressure Test: The most definitive way to check the fuel system is to test fuel pressure.
- Fuel Pressure Gauge: You’ll need a fuel pressure gauge kit that connects to the fuel rail test port (consult your repair manual for location).
- Pressure Reading: Connect the gauge, turn the ignition to “RUN” (or crank briefly as per gauge instructions). Compare the pressure reading to your vehicle’s specifications (found in a repair manual or online).
- Low Pressure: Low or no fuel pressure points to issues like a faulty fuel pump, clogged fuel filter, fuel pressure regulator problems, or fuel line blockage.
- High Pressure (Less Common): Excessively high pressure might indicate a blockage in the fuel return line or a faulty fuel pressure regulator.
- Injector “Click” Test: Fuel injectors spray fuel into the engine cylinders. You can listen for injector operation.
- Stethoscope or Screwdriver Method: Use a mechanic’s stethoscope or place the handle of a long screwdriver on each fuel injector and the other end to your ear.
- Listen for Clicks: While someone cranks the engine, listen for a faint “clicking” sound from each injector. Clicks indicate the injectors are likely being pulsed by the ECU. No clicks could indicate injector wiring issues or ECU control problems.
- Fuel Filter Check: A clogged fuel filter can restrict fuel flow. Fuel filters are maintenance items and should be replaced periodically. If it’s been a while since your last fuel filter change, consider replacing it, especially if fuel pressure is low.
2d: Timing Belt/Chain Check (Less Common for Sudden No Start)
While less common for a sudden no-start issue, a broken timing belt (or chain) will prevent the engine from running. However, timing belt issues usually present with other symptoms before a complete no-start.
Diagnosis & Action (If other steps haven’t resolved the issue):
- Visual Camshaft Rotation Check: This is a basic check and not foolproof, but easy to do.
- Remove Oil Filler Cap: Remove the engine oil filler cap.
- Observe Camshaft: Look down into the oil filler hole at the camshaft or valvetrain components.
- Have Someone Crank Engine Briefly: Have someone crank the engine for a few seconds while you observe.
- Camshaft Rotation? You should see the camshaft or related components rotating if the timing belt/chain is intact and turning.
- No Rotation: If you see no rotation while the engine is cranking, it could indicate a broken timing belt/chain. However, other issues can also cause this, so further investigation is needed.
- Professional Timing Belt/Chain Inspection: A thorough timing belt/chain inspection often requires removing valve covers or timing covers. This is best left to a qualified mechanic.
Conclusion: Systematic Diagnosis is Key
This car not crank diagnosis chart provides a structured approach to troubleshooting no-start issues. By systematically following these steps, starting with the basics and moving towards more complex systems, you can effectively diagnose many common causes of a car that won’t crank or start.
Remember:
- Safety First: Work safely around car batteries and fuel systems. Disconnect the negative battery terminal when working on electrical components (unless specifically instructed otherwise for a test).
- Consult Your Repair Manual: Your vehicle’s repair manual is an invaluable resource for specific component locations, wiring diagrams, and diagnostic procedures.
- When to Seek Professional Help: If you are uncomfortable with any of these steps, or if you’ve gone through these checks and still can’t find the problem, it’s always best to consult a qualified mechanic for professional diagnosis and repair. Incorrectly diagnosing or attempting repairs on complex systems can potentially cause further damage.
By using this car not crank diagnosis chart as your guide, you’ll be well-equipped to tackle common no-start problems and get your car running again.
