The only truly reliable way to check the condition of a timing belt is to replace it according to the manufacturer's recommended service interval. This interval is typically specified in the owner's manual and is usually based on mileage or time, whichever comes first. Ignoring this is risky.
However, some *indirect* indicators might suggest a problem (but don't confirm a bad belt!):
* Engine Misfires/Running Rough: This is a common symptom of a timing belt problem *if* it's slipped or broken. However, misfires have many causes, and this is not a specific indicator of a timing belt issue.
* Unusual Noises: A slapping or knocking sound from the engine could indicate a problem, but again, this could stem from many sources.
* Check Engine Light: A check engine light might illuminate if the engine's timing is off, but it won't explicitly say "bad timing belt." A diagnostic scan is needed to determine the specific problem.
* Visible Damage (Cracks, fraying, missing teeth): As mentioned earlier, these are obvious signs of a problem. But the absence of these doesn't mean the belt is good.
In short: Don't try to "check" a timing belt for failure. Instead, replace it according to the manufacturer's recommended schedule. This is far safer and cheaper than repairing catastrophic engine damage resulting from a failed timing belt. If you suspect a problem based on the indirect indicators above, take your vehicle to a qualified mechanic for diagnosis and repair. A broken timing belt can cause significant internal engine damage, including bent valves.
