My problem was I had intermittent/low voltage (switched 120 volt "SW LINE") on "A" as measured on the wire between on the spark module and Simmer Control module https://www.appliancepartspros.com/bosch-control-unit-422882-ap3672574.html.

It was the relay on the Simmer Control module. This is important because the Simmer Control module non H-A version in no longer available. If you have an SQ003 "H" non "H-A" version you will have to either send it to a rebuilder company or fix it yourself. I pulled the relay and burnished the contacts. After opening the relay I stuck a knife between the contacts and pushed them together and moved the knife back and forth to clean and burnish the contacts. It works! I also just ordered a relay to try if I need it in the future (Relay HJR-3FF 48VDC) $2 including shipping from China; Found it on E bay.

I also had a bad Pot #189816 (no longer available). No gas was coming out of one of the XLO burners (no click and gas sound when you turn it on). Check the voltage to the relay, common problem). Again no part available, I had to pull the pot apart and fix an open connection on the pot board. The pot wiper arm cuts the pcb trace over time. You can use this conductive paint to repair the pot board. MG Chemicals 842AR-P Silver Conductive Pen

Neither XLO burner was working. We replaced the simmer control module. (00619016). The back XLO burner will now light, but simmer control is not working correctly. It shuts off and tries to re-light (we can hear the sparking), but it doesn't light. The front XLO burner won't light at all. We replaced the spark module (00619017) for the front XLO burner and it still doesn't light. My next thought would have been the potentiometer for the front burner, but the fact that XLO still isn't working on the back burner has me wondering. Need some advice before we replace every part on the stove!