You will need to supply more information as to what kind of vehicle, make, year and engine size. There is no standard place for every manufacture.
In the Power Distribution Box ( which is " live " ) located in the engine compartment Full size relay ( # 304 ) is the PCM relay according to the Owner Guide
On a 2000 Lincoln LS : In the FRONT power distribution box ( which is " live " ) located in the engine compartment ( on the passenger side of the engine compartment ) ( relay # 14 is for the PCM power )
On a 2001 Ford Ranger : In the Power Distribution Box ( which is " live " ) located in the engine compartment , on the drivers side ( the # 54 relay is the relay for the Powertrain Control Module / PCM )
Power Control Module
1996 ford thunderbird pcm power relay location?
On a 1999 Ford F-150, the Powertrain Control Module (PCM) relay is typically located in the power distribution box under the hood. This box is situated near the driver's side of the engine compartment, close to the battery. You can identify the relay by checking the diagram on the cover of the distribution box, which will indicate the exact position of the PCM relay.
in the power distribution box under the hood
The power control module (PCM) is the brain of the vehicles engine functions. The relay is a module as part of its power supply circuit.
On a 2004 Ford Ranger ( for the 3.0 and 4.0 liter V6 engines ) In the power distribution box ( which is " live " ) in the engine compartment ( # 47 is the PCM relay ) ( # 48A is the fuel pump relay )
The 1991 crown Victoria has several relays group in a relay center loacated under the hood near the master brake cylinder. In this relay center its the air conditioning WOT cutout relay, fuel pump, PCM power relay, and PCM power diode. P.S. defective relays must be replace as a unit.
Is the device (relay) that provides power to the Power Control Module, if this fails the car will be unable to start
On a 1995 Ford F-350 Power Stroke 7.3 diesel, the PCM relay is located in the Power Distribution Box (PDB) under the hood. Specifically, it's situated near the driver's side of the engine compartment. The PDB contains several fuses and relays, and the PCM relay is typically labeled for easy identification. If you're looking for it, consult the diagram on the inside of the PDB cover for precise location details.