Why does knock sensor keep vehicle from starting


Asked by Jul 31, 2015 at 07:43 PM about the 2003 Buick Rendezvous

Question type: Maintenance & Repair

10 Answers


When the knock sensor senses a tap,it shuts motor down to keep damage from engine.

1 out of 1 people think this is helpful.

Only when it's been drvning around and is warm when it cools it starts rte up

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The sensor gets hot and retards the timing hense the no start out of time

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Yes, Joe in a way it does, show when timing is off all so,it is about like a cam or crank sensor,it is a pulse signal,which goe,s to the ECM,and control firing and fuel in turn shutting it down if there is a issue with any of these.


The knock sensor is like a microphone. It listens to the engine and if it hears spark/knock or pinging it sends a signal to the computer. The computer then begins retarding the ignition timing until the pinging stops and the knock sensor stops sending the signal. If you use cheap gas and the engine pings as a result the computer compensates for it as I've explained. Now if the engine develops a valve tap or other noise the knock sensor can pick that up too. When this happens, as did on my '93 Caprice, the ignition timing will be severely retarded and effect engine performance. But it will not cause a no start condition. You'll get loss of power, running hot, boiling over when the engine is shut off, and possibly popping back through the throttle body. But, again, it'll still start. I'd suggest checking for a no spark condition when your Buick refuses to start. Sounds like the ignition control module is getting hot and breaking down. HTH. -Jim

Bob Beaman

Knock sensor will not prevent it from starting.

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What about the 02circuit no activity detected bank 1 sensor 1

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No, it will just keep the engine in open loop operation. But it'll still start and run. HTH -Jim


What about the ignition relay


Let's start with the basics. Spray some starting fluid down the throttle body and see if it'll run a few seconds on the starting fluid. If it does, you have spark (ignition) but no fuel. If it won't run off the starting fluid you don't have spark or compression. Check for spark first by removing one spark plug wire and sticking large screwdriver in the end of the spark plug wire that plugs onto the spark plug. Be sure that the screwdriver has a plastic or wooden handle so you don't get a powerful shock! Hold the metal part of the screwdriver close to something metal that's not painted while a helper cranks the engine. The exhaust manifold works well for this test. As the engine is cranking you should see and hear a strong spark jump from the screwdriver to the exhaust manifold. It will sound like SNAP-SNAP- SNAP. If you have spark and it wouldn't run on the starting fluid time for a compression test. If all cylinders test low or zero it's jumped timing and won't run until the timing chain and sprockets are replaced and the valve timing is properly set. HTH. -Jim

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