when attempting to downgrade 4g LTE Modem firmware from 17.5.526 to lower versions, it stuck at 70% and then failed.

when attempting to downgrade 4g LTE Modem firmware from 17.5.526 to lower versions, it stuck at 70% and then failed.> show system firmware    
Part             Type              Tag Current               Available             Status
                                       version               version
FPC 1           
PIC 0            MLTE_FW           1   17.5.526              17.5.517              PROGRAMMING  (75%)  <<-----------------------
Routing Engine 0 RE BIOS           0   3.9                   3.9                   OK                
Routing Engine 0 RE BIOS Backup    1   3.9                   3.9                   OK                

root> show system firmware    
Part             Type              Tag Current               Available             Status
                                       version               version       
FPC 1           
PIC 0            MLTE_FW           1   17.5.526              17.5.517              UPGRADE FAILED    <<---------------------
Routing Engine 0 RE BIOS           0   3.9                   3.9                   OK                
Routing Engine 0 RE BIOS Backup    1   3.9                   3.9                   OK 

The LTE card with type of new Sierra Mode (Sierra Wireless MC7430 at REV10) which shipped with firmware 17.5.526 by default, and could not be downgraded to the earlier versions. The downgrade would fail with the following errors: 

[Tue Jun 27 04:23:33.873 LOG: Err] LTE FW: modem FW upgrading failed                 <<<<<<<<<<<<<<<
[Tue Jun 27 04:23:33.873 LOG: Debug] mlte_handle_lte_event: handle event 6
[Tue Jun 27 04:23:33.873 LOG: Err] LTE FW: modem FW upgrading failed
[Tue Jun 27 04:23:33.873 LOG: Debug] mlte_handle_lte_event: handle event 5
[Tue Jun 27 04:23:33.873 LOG: Err] LTE FW: mPIM FW upgrading failed, error code 0        <<<<<<<<<<<
https://gnats.juniper.net/web/default/1742908
 

Please use the following commands to check the confirm the card type and REV into: 

> show modem wireless firmware cl-1/0/0
LTE mPIM firmware details
 Product name: Junos LTE mPIM
 Serial number: AL11035431
 Hardware version: AcceleratedConcepts/Juniper 07
 Firmware version: 17.5.517
 MAC: 40:8f:9d:ef:64:ca
 System uptime: 4743113 seconds
Wireless modem firmware details
 Modem firmware version: 9999999_9904890_SWI9X30C_02.24.05.06_00_TELSTRA_002.026_000
 Modem Firmware build date: 19/05/2017
 Card type: MC7430  <<-------------
 Modem manufacturer: Sierra Wireless, Inc     <<---------
 Hardware version: 1.0   

> show chassis hardware detail no-forwarding
Hardware inventory:
Item             Version  Part number  Serial number     Description
Chassis                                CW2223AN1318      SRX320
Routing Engine   REV 0x10 650-077892   CW2223AN1318      RE-SRX320
  da0    7640 MB  USB Flash Module                       Nand Flash
  usb0 (addr 1)  product 0x0000 0      vendor 0x0000     uhub0
  usb0 (addr 2)  product 0x0046 70     vendor 0x1370     umass0
FPC 0                                                    FPC
  PIC 0                                                  6xGE,2xGE SFP Base PIC
FPC 1            REV 10   650-073957   AN26059514        FPC      <<<------------------
  PIC 0                                                  LTE for AA mPIM
Power Supply 0

LTE firmware 17.5.526 is compatible with with Junos 23.1R1 or higher versions ONLY. Currently Junos 23.1R1 is not available on Juniper Download Page. Customers who uses SRX320 with the new LTE module should reach JTAC for the installation package of Junos 23.1R1

https://gnats.juniper.net/web/default/1712197#audit_tab

> Obtaining Junos OS Release 23.1 for SRX320 mPIM (KB73776 [juniper.net])
https://supportportal.juniper.net/s/article/Obtaining-Junos-OS-Release-231-for-SRX320-mPIM

> [SRX] jFirmware upgrades for SRX Branch Series Mini-PIM（KB35788 [juniper.net]）
https://supportportal.juniper.net/s/article/SRX-jFirmware-upgrades-for-SRX-Branch-Series-Mini-PIMs