Failed Sensors
Knock Sensors
These sensors are a big deal on any performance car. Engine knock, and pre-ignition are two terms for the same phenomenon; it leads to detonation. Pre-ignition happens when the spark plugs fire too soon in the engine cycle, caused by too advanced ignition timing.
Detonation happens when uncontrolled pre-ignition causes a hot spot in the combustion chamber, turning your engine into a self-igniting machine. Detonation causes catastrophic damage to your engine. The only answer to detonation is to take your foot off the throttle, but the damage is probably already done.
The central computer (Body Control Module) wants to advance the timing for the best performance and fuel mileage. When the knock sensors notice the slightest knock, the BCM retards ignition timing to stop the progression from pre-ignition to detonation. So, the ignition timing on your C5 constantly moves forward and back in response to information the BCM receives from other sensors. This system works well; modern Corvette engines make great power and use less fuel than previous generations.
If you hear a sound like someone repeatedly tapping on your engine with a hammer, that is knock. But like any mechanical device, knock sensors can fail. Drive gently to our shop at your earliest convenience to have these critical devices replaced before expensive repairs result.
Oxygen Sensors and Catalytic Converters
These components are critical to efficient engine operation. Catalytic converters are installed in each bank’s four cylinders’ exhaust stream. There is an O2 sensor both in front and behind each catalytic converter. The catalytic converter is there to turn the products of combustion we call smog, into non-harmful materials.
When you burn anything in the presence of nitrogen (most of our atmosphere), you produce nitrogen oxides. The worst of these, nitrogen dioxide (NO2), gives us the harmful effects of smog. Catalytic converters turn smog back into pure nitrogen and pure oxygen nearly instantaneously.
The front O2 sensor measures the oxygen in the exhaust stream and reports it to the BCM (central computer). If the fuel/air mixture is correct, no unreacted oxygen will be in the exhaust stream. Based on information from the front O2 sensor, the BCM adjusts the fuel injected into the combustion chambers to maximize performance and minimize fuel burn.
The oxygen sensor behind the catalytic converter again measures the O2 content of the exhaust stream. The BCM expects the O2 content to increase if the Cat operates correctly, as the Cat is supposed to change NO2 into pure oxygen and pure nitrogen.
If the numbers don’t meet specifications, a check engine light is triggered; when we investigate, we find a message suggesting we replace the Cat. Likewise, when the O2 sensors report nonsensical readings, a check engine light will illuminate, and our diagnostic computer will tell us to replace the oxygen sensor.
You can drive with these parts malfunctioning, but you will get poor gas mileage, fouled spark plugs, and you will be unable to pass a smog check. Call us to visit our website for an appointment to have these repairs or any other work done to your C5 by a mechanic who loves Corvettes as much as you do.
