What is the Top Dead Center (TDC) Sensor all about?

Every engine, whether a single cylinder engine or a V8 engine, has top dead center. This position is a reference point for engine timing and indicates when a spark plug should fire, igniting the fuel the cylinder’s combustion chamber. Top dead center is when the piston is at the very top of its compression stroke. At this position, the intake and exhaust valves in the cylinder head are closed and the air-fuel mixture is compressed in the cylinder. The TDC sensor monitors a reference point on the camshaft that indicates where top dead center is on a cylinder, usually cylinder number one. It sends a signal to the engine control module which, in turn, communicates to send a spark to the cylinder at top dead center. The spark ignites the fuel and the power stroke begins as the piston is forced downward. The TDC sensor is an electrical component and is prone to failure due to corrosion, cracking, or wearing out. If that occurs, the engine control module may not receive a correctly timed signal and the spark may be sent to the wrong cylinder at the wrong timing, causing your engine to run rough or not run at all.

Keep in mind:

• The top dead center (TDC) sensor is integral to the proper timing of your vehicle. If it is installed incorrectly, your vehicle will not run or run very poorly.

How it's done:

• The vehicle battery is disconnected
• The defective top dead center sensor is removed
• The new top dead center sensor is installed
• The battery is connected and the engine is scanned and cleared of codes
• The repair is verified and the vehicle is road tested for proper operation

Our recommendation:

If your car’s Check Engine light turns on, or if the engine will not run or runs poorly, have one of our expert mechanics inspect the problem and replace the TDC sensor if required.

What common symptoms indicate you may need to replace the Top Dead Center (TDC) Sensor?

• Engine will not fire or run
• Engine runs poorly and misfires
• Check Engine light is on
• Backfiring is heard from the exhaust

How important is this service?

Since the TDC sensor is integral to a running engine, it is important to address the operating issues associated with it as soon as possible. Other than a possible stalling condition, there are no associated safety concerns with the TDC.