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The most common cause of this is a bad crankshaft position sensor. When they go bad, the may or may not set a code.
Take a look through these links:
Here is a link that shows in general how one is replaced:
Now, here is what I need you to do. When it doesn't start, you need to check one of two things. Either check for spark to the plugs or if you have a live data scanner, check for an RPM signal. Here is a link that shows how to check for spark:
If you find there is no spark or there is no RPM signal while cranking, here are the directions for replacing the sensor. Note that the sensor on this engine is not behind the crank pulley but rather on the side of the engine. See pics.
2012 Dodge or Ram Truck RAM 1500 Truck 2WD V6-3.7L
Crankshaft Position Sensor - Removal (3.7L)
Vehicle Powertrain Management Sensors and Switches - Powertrain Management Sensors and Switches - Computers and Control Systems Crankshaft Position Sensor Service and Repair Removal and Replacement Crankshaft Position Sensor - Removal (3.7L)
CRANKSHAFT POSITION SENSOR - REMOVAL (3.7L)
See Pic 1
The Crankshaft Position (CKP) sensor is mounted into the right rear side of the cylinder block . It is positioned and bolted into a machined hole.
Disconnect sensor electrical connector.
Remove sensor mounting bolt (1) .
Carefully twist sensor (2) from cylinder block.
Check condition of sensor O-ring (3).
Crankshaft Position Sensor - Installation (3.7L)
Vehicle Powertrain Management Sensors and Switches - Powertrain Management Sensors and Switches - Computers and Control Systems Crankshaft Position Sensor Service and Repair Removal and Replacement Crankshaft Position Sensor - Installation (3.7L)
CRANKSHAFT POSITION SENSOR - INSTALLATION (3.7L)
pic 1 also
Clean out machined hole in engine block.
Apply a small amount of engine oil to sensor O-ring (3).
Install sensor into engine block with a slight rocking and twisting action.
Before tightening the CKP sensor mounting bolt, be sure the sensor is completely flush to the cylinder block. If the CKP sensor is not flush, damage to the sensor mounting tang may result.
Install mounting bolt and tighten to 28 N m (21 ft. lbs.) torque.
Connect electrical connector to sensor.
The Cam/Crank Variation Relearn procedure must be performed using the scan tool anytime there has been a repair/replacement made to a powertrain system, for example: flywheel, valvetrain, camshaft and/or crankshaft sensors or components.
Note that a relearn must be performed when this part is replaced. It will require a special scanner to do. In most cases, the engine will run, but you may notice some driveability issues.
Let me know if this helps or if you have other questions.
Sunday, November 3rd, 2019 AT 8:50 PM