C1246 Diagnostic Code on 1999 Chevrolet Venture (3.4L V6) with ABS and Brake Warning Lights

Hello, I live in Belgium and own a 1999 Chevrolet Venture (locally known as a 'Chevrolet Transsport') equipped with a 3.4L V6 engine. Recently, the ABS, traction control (TC), and brake warning lights have come on simultaneously. I took it to a mechanic who scanned the vehicle and retrieved code C1246, which reads: "Rear ABS channel will not move". This indicates that the rear ABS module is unable to adjust or function properly in one of its channels. I suspect the ABS control module may be faulty. A few weeks ago, the warning lights activated. After a basic inspection, we discovered that the rear right brake was not responding at all—while the front brakes worked normally. We initially suspected a clogged brake line, so we inspected all connections from the calipers to the ABS module. During this process, we found that the ABS module was completely blocking hydraulic fluid flow to the rear-right brake cylinder—even when the ignition was off. After several days, the brake pedal unexpectedly became fully soft and went all the way down. Bleeding the rear-right brake line resolved the issue. We believe the ABS module may have suddenly unblocked the line, allowing air to enter the system due to our prior disconnection. Given this history, I now suspect a failing ABS control module. However, I’d like to confirm whether there are any electrical or hydraulic circuit issues that could be causing this behavior before concluding it’s a failed module. Any insights on how to diagnose these circuits (electrical or hydraulic) would be greatly appreciated. Thank you for your help! Best regards, Dieter