Car symptom
Black smoke from the exhaust
Black smoke is unburned fuel — the mixture is too rich.
Most likely causes
- Clogged air filter
- Dirty or faulty MAF sensor
- Leaking injector
- High fuel pressure
- Bad oxygen sensor
Checks to run
- Inspect the air filter
- Read live fuel trims
- Test fuel pressure
- Check injectors
Tools you may need
OBD-II scanner
Fuel pressure gauge
Confirm before replacing. These are hypotheses to check — never buy parts on a guess. If the fault involves brakes, airbags or fuel under pressure, use a professional.
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FAQ
It depends on the cause. Some causes are cheap and quick; others (like a head gasket or seized caliper) need attention soon. Work through the checks in order and confirm before replacing parts.
Start with the free checks listed here. If they involve high voltage, fuel under pressure, airbags or brakes, let a professional handle it.
The interactive diagnostic asks targeted questions to narrow it down, and every cause must be confirmed with a measurement — never guess.