P0340 - Camshaft Position Sensor Circuit Malfunction
It's important to understand diagnostic fault codes never say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. In this case there's a 50 percent chance the camshaft position sensor is failing. First your mechanic will want to rule out wiring and connector terminal problems.
Most models use a crankshaft position sensor and a camshaft position sensor. On older models starting in the late '80s, signals from both of them had to show up at the Engine Computer for the engine to run. If either one failed while driving, the engine would stall.
By around 2000 to 2002, if one sensor failed while driving, the engine would continue to run because the computer simply calculated which cylinders to fire next, and kept going in order. It was once you stopped the engine, the computer didn't know which cylinders to start with, so the engine would not restart.
One important note about both of these sensors on all car brands is they often fail by becoming heat-sensitive, then they work again after cooling down for about an hour. The most common story is the engine runs fine as long as you're driving, then it won't restart after stopping for a short time, as in when stopping for gas. While driving, natural air flow keeps the sensors cool. When you stop, engine heat migrates up to the sensors and can cause one to fail until it cools down. We call that "hot soak".
My understanding is the latest modification to the strategy is the engine will run with one failed sensor, but in back-up mode, by relying strictly on the other sensor. I don't know what year that started.
It's important to not erase the fault codes or disconnect the battery until you know what the exact code numbers are, otherwise that valuable information will be lost. Erasing the codes doesn't reset anything or make the problem go away. The goal is to keep the codes stored in the computer for your mechanic's reference. Most will not rely on your memory to make a preliminary diagnosis. They know that if you remember wrong, whose fault will it be when they spend your money searching in the wrong area?
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Saturday, April 13th, 2019 AT 9:57 PM
