if it bolts on the starter assembly you are probably talking about the starter solenoid. basically its what makes the starter engage. if its a sensor that just bolts near the starter it could be anything from a crank position sensor to a knock sensor.
It is the knock sensor. It retards the timing if the engine pings or rattels.
It sits behind the starter on the drivers side of the engine. You will have to remove the starter in order to see it.
Need to know what engine you have, the 2.5, 2.8 or the 4.3.
I have a 08 Chevy Cobalt. It took me about an hour and a half to replace the crank position sensor. Disconnect your battery and unbolt your starter; you can leave the starter wired up just move it out of your way. The sensor sits behind the starter. Be careful when disconnecting the plug for the sensor so you don't break it. You can disconnect is from up top so you can see what you're doing. Replace sensor, replace starter, reconnect your battery, and your back on road.
Solenoid
crank sensor located on the front of the motor left of the starter and above the oil filter
Unplug the AIT (air intake temp.)sensor. Remove the air intake ducts from the throttle body and air filter box. Undo the battery cables( i always undo both just to be safe) Look at the starter,there will be two bolts (15mm i believe) that mount the starter to the transmission. Remove those. Move the starter towards the passenger side alittle to dislodge it from the hole that it sits in. Now convince the starter YOU WILL GET TOTHE BACK SIDE OF THE STARTER. When you can see the wires at the back,count the little wires,so you can put all of them back. Remove the little bolt that hold these little wires on,use a bread tie or something to keep these wires together so you wont have to search for them later if you want to. Then remove the two bigger wires(battery cable & Alt. wire) Remove the starter,look at your hands and say a few new cuss words that you just learned....OR.... you can remove the intake manifold so you can get to the starter with no problems at all. Note that the crank sensor is located behind the starter next to the oil filter and may come unplugged.
it sits by its self on the intake manifold
I believe the starter motor sits in the galley under the intake manifold.
If it's not the crank sensor, it's probably the ECM, and that's bad. Try you crank shaft position sensor, if it is bad the engine will not run. It's on the back of the engine just below the vavle cover on the drivers side You can also try the ignition pickup. It's a little back plastic plate that sits on top of the distributor when you take the cap off.
The starter is under the intake manifold plenum. This is the large black plastic assembly under the engine cover. Ther starter sits in the VALLEY.- TechJK ----------------------------
The starter on the Honda Accord is located in the front of the vehicle. The Honda's motor sits sideways inside the engine compartment. The starter is between the front of the car and the motor.