I fixed the issue with SIMCOM UART. It was another compatibility issue with SDCARD. The GPIO4 and GPIO13 we are using for v3.1 simcom modem are SD_DATA1 and SD_DATA3. Even though I had set SDCARD to 1-line mode, the ESP IDF driver was still reserving all those GPIO pins for itself (at hardware controller level). A 1-line (sic) change to our SD-CARD component fixes this and frees SD_DATA1, SD_DATA2, SD_DATA3 for our other uses. With firmware fix made, I can mount the SD CARD, and run ‘test sd’ while talking to simcom modem. All ok. CAN2 is now also ok. I re-flowed the solder on that part of the board, and all looks good now. OVMS > can can1 start active 1000000 Can bus can1 started in mode active at speed 1000000Kbps OVMS > can can2 start active 1000000 Can bus can2 started in mode active at speed 1000000Kbps OVMS > can can3 start active 1000000 Can bus can3 started in mode active at speed 1000000Kbps OVMS > can log trace CAN logging active: Type:trace; Path:''; Filter:off; Vehicle:; Note: info logging is done at log level debug, frame logging at verbose OVMS > log level verbose Logging level for * set to verbose OVMS > can can1 tx standard 100 01 02 03 04 V (66710) canlog: TX can1 id 100 len 4: 01 02 03 04 | .... V (66710) canlog: RX can2 id 100 len 4: 01 02 03 04 | .... V (66710) canlog: RX can3 id 100 len 4: 01 02 03 04 | …. OVMS > can can2 tx standard 100 01 02 03 04 V (73230) canlog: TX can2 id 100 len 4: 01 02 03 04 | .... V (73230) canlog: RX can1 id 100 len 4: 01 02 03 04 | .... V (73230) canlog: RX can3 id 100 len 4: 01 02 03 04 | .... OVMS > can can3 tx standard 100 01 02 03 04 V (80380) canlog: TX can3 id 100 len 4: 01 02 03 04 | .... V (80380) canlog: RX can1 id 100 len 4: 01 02 03 04 | .... V (80380) canlog: RX can2 id 100 len 4: 01 02 03 04 | .... OVMS > can can1 status CAN: can1 Mode: Active Speed: 1000000 Interrupts: 4 Rx pkt: 2 Rx err: 0 Rx ovrflw: 0 Tx pkt: 2 Tx delays: 0 Tx err: 0 Tx ovrflw: 0 Err flags: 0 D (88210) canlog: Status can1 intr=4 rxpkt=2 txpkt=2 errflags=0 rxerr=0 txerr=0 rxovr=0 txovr=0 txdelay=0 OVMS > can can2 status CAN: can2 Mode: Active Speed: 1000000 Interrupts: 4 Rx pkt: 3 Rx err: 0 Rx ovrflw: 0 Tx pkt: 1 Tx delays: 0 Tx err: 0 Tx ovrflw: 0 Err flags: 0 D (90770) canlog: Status can2 intr=4 rxpkt=3 txpkt=1 errflags=0 rxerr=0 txerr=0 rxovr=0 txovr=0 txdelay=0 OVMS > can can3 status CAN: can3 Mode: Active Speed: 1000000 Interrupts: 4 Rx pkt: 3 Rx err: 0 Rx ovrflw: 0 Tx pkt: 1 Tx delays: 0 Tx err: 0 Tx ovrflw: 0 Err flags: 0 D (92910) canlog: Status can3 intr=4 rxpkt=3 txpkt=1 errflags=0 rxerr=0 txerr=0 rxovr=0 txovr=0 txdelay=0 So 16MB Flash, 4MB SPIRAM, ESP32, modem, CAN, EGPIO, and SDCARD are all ok. I will test the remaining few peripherals tonight (need 12v power). I think we are going to be ok now. Component orders have been placed. I’m going to order a first batch of 120 modules tonight (assuming no issues with the last few peripherals). Regards, Mark.