Camshaft sensor versus crankshaft sensor

What’s the difference between a camshaft sensor versus a crankshaft sensor?

A camshaft sensor generates the command for spark

DIYers often get confused over the difference between a crankshaft sensor versus a camshaft sensor. They each control a different part of the fuel/spark cycle.

In older engines with a traditional distributor style ignition system, the crankshaft rotated the camshaft(s) via a chain or timing belt, so the two were perfectly synchronized. The distributor was geared to the end of the camshaft. That way, the distributor could generate a spark a certain number of degrees before the piston reached the top of the compression stroke. As car makers moved to solid-state ignition systems, distributor-less ignition systems and coil-over-plug systems they eliminated the distributor and used a camshaft sensor instead. The camshaft sensor generates a spark command based on the location of the camshaft. For details on how a camshaft sensor works, see this post.

A crankshaft sensor generates the command for fuel injection

There was no need for a crankshaft sensor in carbureted cars because the fuel was pulled into the cylinder during the intake stroke. When car makers switch to throttle body, port and direct injection, they needed a way to trigger the fuel injectors at the right time during the intake or compression stroke.

In a throttle body and port fuel injection system, the fuel injectors operate during the intake stroke. In order to time the injectors, the computer must know the exact location of the pistons and it learns that from the crankshaft sensor. Direct injection engines, on the other hand, operate the injectors during the compression stroke. For more details on how a crankshaft sensor works, see this post.

What’s the difference between a camshaft sensor versus a crankshaft sensor? Summary

The camshaft sensor controls ignition timing

The crankshaft sensor controls fuel injection timing

What happens if the camshaft sensor fails?

No start due to no camshaft sensor signal

Engine stalls due to weak or erratic signal

Misfire due to weak or erratic signal

Poor performance/lack of power or poor fuel mileage due to weak or erratic signal

Shifting problems

Check engine light

What happens if the crankshaft sensor fails?

No start due to no fuel

Engine stalls due to no fuel

Misfire due to no fuel or erratic fuel injection

Poor performance/lack of power or poor fuel mileage due erratic fuel injection

Shifting problems

Check engine light

©, 2018 Rick Muscoplat