It reads off of the flexplate teeth that the starter uses. Technically it is the Engine Speed Sensor. You can see the loom that goes to it in this picture, by the oil filter. The other end is a plug, up behind the left side cam cover.
This is sort of spelled out above, but to be clear:
There are two sensors. The CPS or Crank Position Sensor and the “flywheel sensor” or Engine Speed Sensor. They are both the same part number and are interchangeable.
Either one will cause a “crank but no start” situation on a Marelli ignition car.
The best test is to use an oscilloscope AT THE IGNITION computer in the passenger side footwell. This confirms (or not) sensor function and harness integrity. If no signal at the computer, work backwards from there.
The second best test is to determine (listen with screwdriver or stethoscope) whether or not the injectors are firing. If they are NOT, then likely one of the sensors is not working.
If this was my car and I didn’t have a scope, I would:
- Listen for injectors. If not clicking, assume CPS or ESS is bad.
- Unplug CPS and ESS from harness and use contact cleaner on the plugs, make sure there are definitely good connections. These are very low-voltage and low current signals, they do not tolerate poor connections. As previously mentioned these plugs are next to B-bank t-stat housing and behind B-bank cam cover. They look like fuel injector plugs.
- Ensure that the sensor end of each is tight and clean. Clean with brake cleaner or similar. If they are sloppy in the mount or all gunked up they may not be reliable. Now try to start.
- If still no start, check thin white coaxial wire that is buried in the harness on the left side of the injector rail. There is a spade connector in there that fails. Make sure it is clean and tight. This is part of the ESS harness and is a common failure point. Now try to start.
- If still no start, Buy two new sensors. Replace CPS. If start, save second for spare. If no start, replace ESS.
Regards
Bob