Would a broken o2 sensor couse truck not start?

A broken O2 sensor will almost certainly *not* directly prevent a truck from starting. The O2 sensor measures the oxygen content in the exhaust to help the engine control system optimize the air/fuel mixture. While important for fuel efficiency and emissions, it's not directly involved in the basic starting sequence.

If your truck won't start, the problem lies elsewhere. A faulty O2 sensor might cause poor running *after* the engine starts, but not prevent it from starting in the first place. Other potential causes for a no-start condition include:

* Dead battery: This is the most common cause.

* Faulty starter motor: This cranks the engine but doesn't start it.

* Alternator issues: This prevents the battery from recharging.

* Fuel delivery problems: Blocked fuel filter, fuel pump failure, etc.

* Ignition system problems: Spark plugs, ignition coil, distributor (if applicable), crankshaft position sensor, camshaft position sensor.

* Security system issues: Immobilizer or alarm system problems.

You should have your truck diagnosed by a mechanic to pinpoint the actual cause of the no-start condition. Mentioning the O2 sensor might be helpful if you've noticed other drivability problems before the no-start issue arose.