Peterbilt 579 Radar Fault That Wasn’t a Radar Problem — Full Series I put this series together because my truck was showing Adaptive Cruise Fault / Inspect Radar, disabling cruise control, triggering warning lights, and beeping from the dash. At first it looked like a radar problem, but the real issue was deeper in the air brake / ABS system. Here is the full series: Part 1 — When a Radar Fault Wasn’t a Radar Problem Link: https://truckaid.app/qa/view.php?id=85 Part 2 — The Air Dryer Clue Link: https://truckaid.app/qa/view.php?id=86 Part 3 — The ABS Fault Was the Missing Piece Link: https://truckaid.app/qa/view.php?id=87 Part 4 — The Repair and Final Lesson Link: https://truckaid.app/qa/view.php?id=88 Part 5 — Final Lesson index Link: https://truckaid.app/qa/view.php?id=89 Final **lesson: Do **not replace the radar first just because the dash says radar. On these newer trucks, adaptive cruise and collision mitigation are tied into the ABS and brake system. If the ABS system has a fault, the truck may disable radar-based cruise and make it look like a radar issue. In my case, the chain looked like this: Air dryer heater problem → water in air tanks → ABS sensors/modulators affected → ABS fault 802 / Relay Diagonal 1 → adaptive cruise/radar disabled → cruise control disabled and dash beeping → sensors and steer axle ABS modulator parts repaired → problem gone Hopefully this helps another driver save time, money, and frustration.