Car Won't Start but Has Power: What It Means and What Happens Next

Turn the key or press the button and pay attention to what the engine does. If the starter spins the engine over but it never catches, you have a crank-no-start. If the engine does not turn over at all, whether you hear a click, a hum or nothing, you have a no-crank. Those two symptoms are handled by different parts of the car and are diagnosed in different ways, so this is the first thing we will ask.

Having power, meaning the dash lights up and the radio plays, only tells you the battery has enough charge to run small loads. Interior electronics draw a few amps. A starter motor draws hundreds. A battery, a cable or a connection can pass the first test and fail the second, which is why bright headlights never rule out the battery.

Also note what else is happening. A key-shaped or padlock-shaped light that stays on or flashes, a message about the key not being detected, or a car that cranks and dies after a second are details that go straight into the diagnosis.

When the engine will not turn over, the fault is somewhere between the battery and the starter motor, or in the logic that decides whether to allow a start. The usual groups:

• Weak battery, corroded terminals or a bad ground. The most common group by a wide margin, even with the lights on. A battery can look fine at rest and collapse under starter load, and a loose or crusty terminal or a corroded ground strap does the same thing.
• Starter motor, relay or fuse. The motor itself wears out, and the relay and fuse that feed it can fail. A tired starter can also be inconsistent, working one day and refusing the next.
• Neutral safety switch or clutch switch. An automatic will not crank unless the computer sees park or neutral. A failing range switch, or the clutch pedal switch on a manual, blocks the start with everything else fine.
• Ignition switch or start button. Worn contacts in the switch, or a fault in the start-button circuit, mean the crank request never reaches the relay.
• Immobilizer not recognizing the key. If the transponder in your key does not answer correctly, most cars refuse to crank, or crank and immediately shut off. This is the group your second key can rule in or out.

Each group has its own price, from a cleaned terminal to a new starter, and each is tested differently, which is why a no-crank should be measured rather than guessed at.

If the engine spins but never fires, the battery and starter are doing their jobs. Now the engine needs three things at once: fuel, spark and the right timing between them. The computer also needs valid signals from its sensors before it will supply either.

• Fuel delivery. A failed fuel pump, a dead pump relay, a blown fuse or a clogged filter leaves the engine with nothing to burn. On direct-injection engines the low-pressure side can be fine while the high-pressure side is not.
• Spark. A failed ignition module, a wiring fault or a lost sensor signal means no spark at any cylinder.
• Crankshaft or camshaft position sensor. Without a valid signal from these sensors the computer does not know the engine is turning and will not fire injectors or coils, so the engine cranks normally and never catches.
• Immobilizer cutting fuel or spark. On many makes an unrecognized key allows cranking but disables the injectors or ignition. From the driver's seat it looks exactly like a fuel or sensor problem, which is why key faults get misdiagnosed as engine faults.
• Timing. A snapped belt, a jumped chain or a sheared cam gear stops the valves from moving in step with the pistons. On many engines continued cranking in this state does further damage, which is one reason not to keep trying.

Four of these five groups produce the same sound from the driver's seat. The parts range from a relay to an engine repair, and nothing about the symptom alone says which you have.

Two things cost nothing and can save a tow. Try your second key. If the spare starts the car, the first key has a dead or damaged transponder or has lost its pairing, and that is a key programming job, not an engine repair. Look at the battery terminals. If they are visibly loose or coated in corrosion, say so when you call, because it changes where the diagnosis starts.

Then write down what happened: whether it cranks, which lights or messages appeared, and whether the engine was hot or cold. Note anything that changed recently, such as a dead battery, a jump start, a new fob battery or recent repair work. That record is worth more to the technician than any part you could buy.

What is not worth doing: cranking for long stretches, which cooks the starter, drains the battery and floods the engine, or buying a battery or a starter because a forum said so. Do not clear fault codes or disconnect the battery either, because that erases the stored record of what the car saw when it refused to start. A no-start that arrives untouched is diagnosed faster and cheaper than one that has had three parts thrown at it.

Most cars built in the last two decades have an immobilizer. The key carries a transponder chip, the car reads it when you turn the key or press the button, and a security module decides whether to allow the engine to run. When that handshake fails, the car behaves like it has a mechanical fault, but nothing mechanical is wrong.

A key or padlock light that stays lit, a message that the key is not detected, or trouble that began right after a dead battery, a jump or a fob battery change are all worth mentioning when you book. A worn key, a damaged chip, a failed antenna ring around the ignition or a corrupted security module can all cause it. Each is confirmed with the factory tool, not by replacing parts.

The fix might be as simple as pairing a new key, or it might mean programming a replacement body or engine control module and tying it to the immobilizer. Our mobile car key programming service handles key work at your driveway or parking lot, and we add a key without erasing the ones you already have. Module work happens at the shop.

Our Electrical and No-Start Diagnosis starts at $150 and is done at our Massachusetts shop, so a car that will not run arrives on a tow or flatbed. It is a structured process rather than a guess, and it ends with a written report.

We confirm the battery, charging system and starter circuit under real load rather than taking the dash lights at their word. If the engine cranks, we use the manufacturer's own diagnostic software to see what the engine computer sees while it is trying to start. That tells us whether fuel, spark and the sensor signals are all present without pulling the engine apart. We read the security system directly to learn whether the key was accepted and a start was authorized. If the data or the sound of the engine suggests a timing failure, we confirm it by measurement before anyone opens the engine.

The report lists fault codes by module, the measurements, the root cause and the recommended repair. Most no-start jobs are finished the same day. If the answer is a key or a module rather than a mechanical part, we quote that work on the spot.

Note whether the car cranks, what lights or messages appear, and whether anything changed recently, such as a dead battery or a new fob battery. Then book an Electrical and No-Start Diagnosis in Massachusetts from $150, or if the second key starts the car, skip straight to key programming.

South Shore drivers can start on our Quincy diagnostics page. Call (617) 383-9331 or send a free quote request and you will have a firm price within 2 hours.