What is a PCM - 1996 Chevrolet Impala SS

Do you know that a replacement ECM would need programming ? Dealer .An it's a PCM - powertrain control module ,because transmission an engine modules are inside the same box (module) .Service of the PCM should normally consist of either replacement of the PCM or EEPROM programming. If the diagnostic procedures call for PCM replacement, inspect the PCM first to see if the PCM is the correct part. If the PCM is faulty, remove the PCM and install the new service PCM.
The new service PCM will not be programmed. You must program the new PCM. DTC P0602 indicates the EEPROM is not programmed or has malfunctioned.
There are no user serviceable parts in this PCM. The PCM should never be opened for any reason.
Important: When replacing the production PCM with a service PCM (controller), it is important to transfer the broadcast code and production PCM number to the service PCM label. Do not record this information on the PCM cover. Transfer allows positive identification of PCM parts throughout the service life of the vehicle.

Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
Remove the left sheet metal diagonal brace. Refer to Front End Sheet Metal Diagonal Brace Replacement - Left Side in Body Front End.
Remove the air cleaner assembly cover and lift the PCM from the assembly.
Disconnect the harness connectors from the PCM.
Remove the PCM from the engine compartment.

The pcm is just under the battery on the left side of the engine compartment. The PCM need to be calibrated to the truck and motor. If you just put it in the motor may not start. Read over the information I have attached before you do this. Ken Powertrain Control Module Replacement Service of the powertrain control module (PCM) should consist of either replacement of the PCM or electrically erasable programmable read only memory (EEPROM) programming. If diagnostic procedures call for the PCM to be replaced, the replacement PCM should be checked to ensure that the correct part is being used. If the correct part is being used, remove the faulty PCM and install the new service PCM.
Important: To prevent internal PCM damage, the ignition must be OFF when disconnecting or reconnecting power to the PCM. For example, when working with a battery cable, PCM pigtail, PCM fuse, or jumper cables. • Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM module connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM. • The replacement PCM must be programmed.

Removal Procedure

Important: It is necessary to record the remaining engine oil life. If the replacement module is not programed with the remaining engine oil life, the engine oil life will default to 100%. If the replacement module is not programmed with the remaining engine oil life, the engine oil will need to be changed at 5000 km (3,000 mi) from the last engine oil change.

1. Using a scan tool, retrieve the percentage of remaining engine oil. Record the remaining engine oil life.

Really depends on which fuse is out. If the PCM has no power it can not be reprogrammed. The issue is what made the fuse break and why does the Dealership think the PCM needs reprogramming? You do not know if the PCM will work until it is powered up unless certain connection points are tested and it shows the PCM is dead. This would be like saying the insides of your PCM are burnt up. If the PCM is burnt up restoring power will not fix it.

Probably a better way to to say it is you need to know if the PCM was burned up and if that is why the fuse broke. The fuse is suppose to protect the PCM before it is damaged. You could smoke another PCM if you connect it up to the car without repairing the problem first.. But the PCM is a computer and the memory can be lost. But like other computers there are Read only programming and programs which can be rewritten. If the circuits are good then the old PCM can be reprogrammed when power is restored.

If vehicle has been submerged, PCM is likely dead. If vehicle has been struck by lightning, PCM could be locked up or dead. Assuming none of these has happened:
Check power to PCM, not just fuses. You can check through the backside of the connectors ON the PCM.
Check connectors on PCM.
Check ground to PCM.
Make sure you've had no rodent activity on vehicle wiring.
Reset PCM by disconnecting battery (+) lead, waiting 15 seconds, then grounding battery (+) to battery (-) lead. Reconnect battery (+) lead to battery. All user memory sets such as radio and seat settings will be lost.
With no output from PCM, after resetting, the highest probability is dead PCM. It's rare, but it happens.

Flashing Diag Code P0122
TP circuit low input
DETECTION CONDITION
• If PCM detects TP sensor voltage at PCM terminal 89 below 0.10 V after engine start, PCM determines
that TP circuit has a malfunction.
POSSIBLE CAUSE
• TP sensor malfunction
• Connector or terminal malfunction
• Open circuit between TP sensor terminal C and PCM terminal 89
• Short to ground circuit between TP sensor terminal C and PCM terminal 89
• Open circuit between TP sensor terminal A and PCM terminal 90
• Short to ground circuit between TP sensor terminal A and PCM terminal 90
• PCM malfunction

Flashing Diag Code P0123
TP circuit high input
DETECTION CONDITION
• If PCM detects TP sensor voltage at PCM terminal 89 is above 4.77 V after engine start, PCM determines
that TP circuit has a malfunction.
POSSIBLE CAUSE
• TP sensor malfunction
• Connector or terminal malfunction
• Open circuit between TP sensor terminal B and PCM terminal 91
• Short to reference voltage (Vref) supply circuit between TP sensor terminal C and PCM terminal 89
• PCM malfunction

Right. Just like you said should work. Connect pcm, then the battery.

Service of the powertrain control module (PCM) should normally consist of either replacement of the PCM or electrically erasable programmable read only memory (EEPROM) programming. If the diagnostic procedures call for the PCM to be replaced, the PCM should be inspected first to see if the correct part is being used. If the correct part is being used, remove the faulty PCM and install the new service PCM.
Important: To prevent internal PCM damage, the ignition must be OFF when disconnecting or reconnecting power to the PCM. For example, when working with a battery cable, PCM pigtail, PCM fuse, or jumper cables.
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM module connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM.
Removal Procedure

Important: It is necessary to record the remaining engine oil life. If the replacement module is not programed with the remaining engine oil life, the engine oil life will default to 100%. If the replacement module is not programmed with the remaining engine oil life, the engine oil will need to be changed at 5000 km (3,000 mi) from the last engine oil change.

1. Using a scan tool, retrieve the percentage of remaining engine oil. Record the remaining engine oil life.
   

Loosen the PCM harness connector bolts (4) from the center of the PCM harness connectors.
Notice: In order to prevent internal damage to the PCM, the ignition must be OFF when disconnecting or reconnecting the PCM connector.
Remove the PCM harness connectors (2) from the PCM (1).
Remove the PCM retaining bolts (3) and nuts (6).
Notice: Do not touch the connector pins or soldered components on the circuit board in order to prevent possible electrostatic discharge (ESD) damage to the PCM.
Slide the PCM (1) away from the intake manifold past the mounting studs (5) and remove PCM from the vehicle.
Remove the PCM mounting studs (5) from the intake manifold ONLY if replacing the studs.


It is possible that the pcm made need to reflashed after replacement.

PCM is what control's all of your engine sensor's, there's no repair for the PCM, but to replace.

here are instructions from autozone.com:

REMOVAL & INSTALLATION See Figures 1, 2, 3, 4, 5, 6, 7 and 8

Fig. Fig. 1: The PCM is mounted behind the fender, adjacent to the EVAP canister

Fig. Fig. 2: Remove the module-to-bracket retaining screws and ...

Fig. Fig. 3: ... remove the PCM (1) from the mounting bracket (2)

Fig. Fig. 4: Detach the PCM electrical connectors

Fig. Fig. 5: Remove the PCM (2) from the retainer (1)

Fig. Fig. 6: The EPROM cover is retained by two screws

Fig. Fig. 7: Remove the EPROM cover, if the seal tears, this is normal, do not apply an adhesive to the pad, the adhesive could drip onto the circuitry and ruin the PCM

Fig. Fig. 8: Remove the EPROM by squeezing the two tabs and carefully separating the EPROM from the PCM

1. Turn the ignition switch OFF .
2. Disconnect the negative battery cable.
3. Remove the right hand engine splash shield.
4. Unfasten the horn attaching bolt, then detach the electrical connector and remove the horn.
5. Unfasten the module-to-bracket retaining screws, then slide the PCM out of the mounting bracket.
6. Detach the electrical harness connectors from the PCM.
7. Remove the retainer from the PCM.
8. If you are replacing the PCM on a 1995-96 model:
   1. Remove the Electronic Programmable Read Only Memory (EPROM) module, also known as the KS module, cover.

WARNING
If the foam pad around the base of the EPROM cover rips during removal, this is normal and should not be remedied by applying any kind of adhesive to the pad. This could ruin the circuitry of the PCM.
WARNING Before removing the EPROM cover, thoroughly clean the outer surface of the PCM to remove any debris that could enter the PCM and cause damage to the circuitry.
WARNING To prevent a possible discharge of static electricity, which could ruin the PCM, do not touch the connector pins or the soldered components on the circuit board.

1. Remove the KS module by squeezing both retaining clips together and at the same time, grasp it at both ends and lift it up out of the socket.

To install:
Before replacement of a defective computer control module, first check the resistance of each PCM controlled solenoid.

1. If the PCM is being replaced, open the package on the new PCM and verify that the PCM numbers match or an updated number is given before you attempt installation.
2. If you have a 1995-96 model:
   1. Install the EPROM into the PCM.
   2. Install the EPROM cover and tighten the retaining screws to 25-28 inch lbs. (3 Nm).
   
   
3. Install the PCM retainer.
4. Attach the module electrical harness connectors.
5. Position the PCM in the vehicle, then install the module-to-bracket retaining screws.
6. Install the horn, attach the electrical connector, then fasten with the horn attaching bolt. Tighten the bolt to 6-9 ft. lbs. (8-12 Nm).
7. Install the right hand splash shield.
8. Check that the ignition switch is OFF , then connect the negative battery cable.
9. Enter the self-diagnostic system and check for trouble codes to be sure the PCM and the KS module are properly installed. For details, refer to the procedure for checking trouble codes.