2012 S60 T5 (2.5L 5cyl) B5254 thinks it’s not in park, won’t start | SwedeSpeed

Removing/installing shifter cable at gearbox should not have messed anything up. Make sure that the electric connector for 313126 in your pic is connected and not knocked loose. This is the transmission brain. The mechanical shift lever goes thru the TCM connects to the valve body inside of the gear box. The TCM reads the position of the lever shaft location at the gear box as well as the gear shift lever inside the car. TCM replace PDF, last pic, shows the correct alignment of the TCM to shift shaft. It is probably not out of alignment; this may need to be checked to verify that it is not the problem. This is a weird problem. The diagnostic path of finding the problem includes a lot of what is not the problem. ECM B10A268 crash code is weird also. When the TCM code get resolved, erasing the ECM code should clear the crash code. The ECM crash code will not let the starter relay kick in. You were very lucky that the drive belt did not get sucked into the timing belt and bend valves. Did you replace the drive belt tensioner. This is what caused the drive belt to slip off. Drive belt tensioner will tilt away from the engine due to tension, age and wear. The drive belt will walk outward and shred to pieces. Did you erase the codes?
Transmission wiring, 3/156=gear shift lever, 8/36=brake pedal interlock, 8/37=TCM.
There are not any fuses for 3/156. 11B/31 TCM under hood fuse is probably OK.
When you move the gear shift lever inside the car, does the DIM PRD123 message change.
Remove the shift cable at the transmission. Manually move the transmission lever into park position.
Do not connect the shift cable. Move the inside gear shift lever into park and see if anything changes.
Why, I don’t know, we have to try something.

CEM-U010100 Lost Communication with Transmission control module. General Failure Information. No sub type information
Diagnostic trouble code (DTC) information CEM-U010100

Condition
The control modules communicate with each other for exchange of information in a network via a standardized serial communication procedure – CAN (Controller Area Network).
The diagnostic trouble code (DTC) is stored if the control module detects that:
Interrupted or missing communication with the Transmission control module (TCM).
The control module’s test for the diagnostic trouble code (DTC) starts in the event of:
Ignition switch position II.
Note! The control module can only detect the fault once the test has been started and the diagnostic trouble code (DTC) is stored when the conditions are met. The diagnostic trouble code (DTC) indicates a fault in the communication across the CAN network and does not isolate an individual node. Do not replace the central electronic module (CEM) unless fault-tracing indicates a damaged control module.
Substitute value
None.
Possible source
Voltage supply to the Transmission control module (TCM) is missing.
Open-circuit in the ground lead to the Transmission control module (TCM).
Contact resistance in the terminals.
Open-circuit or short-circuit in the wiring for the control area network (CAN).
Transmission control module (TCM) is not intended for this vehicle, it may e.g. be used and have another software/hardware.
Hint:
If several diagnostic trouble codes for communication errors with other control modules in the high-speed network are stored in the Central electronic module (CEM), this indicates some common problem in the CAN-network (see wiring diagram).
Fault symptom
No gear shift
Malfunction indicator light (MIL), on
Message in information display

ECM-B10A268 Crash Input. Algorithm Based Failures. Event information, B5254T5
Diagnostic trouble code (DTC) information ECM-B10A268
Condition
Note! This diagnostic trouble code (DTC) status is an event controlled diagnostic trouble code (DTC). An event controlled diagnostic trouble code (DTC) does not mean that there is a fault in the control module when it is active, but is designed as information.
Engine control module (ECM) registers internally if the vehicle has been involved in a collision. If the control module detects that Central electronic module (CEM) sends internal signals that a collision has occurred, the diagnostic trouble code is generated.
Note! The diagnostic trouble code must be erased like a normal diagnostic trouble code, even if fault-tracing is not carried out.
The diagnostic trouble code (DTC) can be diagnosed at key position II.
Substitute value
Nothing.
Possible source
This diagnostic trouble code (DTC) is not caused by a fault that needs to be remedied.
Fault symptom
Engine is difficult to start
Malfunction indicator light (MIL), on
Message in information display