Project S-Type: Fixing C1777 (DSC Not Available) + RPM Hunting | S-Type 3.0 V6 (Part 17)

Jaguar S-Type 3.0 V6 Sport showing “DSC Not Available”, ABS DTC C1777 (Vacuum pressure circuit failure) and a light 100–150 RPM hunting/surge between 30–60 mph once warm? In this episode of Project Jaguar (Part 17) I follow the fault all the way through — including an initial “it’s fixed!” moment, the fault returning, and then the extra steps required to get the car stable again. ✅ Symptoms covered “DSC Not Available” / DSC N/A message ABS DTC C1777 – Vacuum pressure circuit failure Light RPM hunting (100–150 rpm) at ~30–60 mph once up to temperature Transmission behaviour changes that often appeared alongside the DSC event ✅ Fixes performed Replaced XR820798 brake booster vacuum pipe (includes integrated grommet + one-way check valve) Replaced upper and lower intake performance valve seals (C2S40669) Cleared and re-checked DTCs using Jaguar SDD Brake Booster Solenoid recalibration (SDD) after DSC N/A returned Prepared for and completed TCM reprogramming (adaptations cleared as part of the process) ✅ Verification Initial on-drive verification and post-repair SDD scan Fault returned (DSC N/A again!) and was re-diagnosed in the same video Post recalibration test drive + re-scan Post TCM reprogramming: gearbox behaviour improved but still not quite 100% 🧰 Tools used: 8mm socket (1/4") 13mm socket (1/4") Stubby 1/4" ratchet Phillips screwdriver Windscreen arm puller Trim removal kit 🧩 Parts used: XR820798 – S-TYPE 2.5/3.0 V6 (2002–2007) vacuum pipe (with grommet + check valve) 2* C2S40669 – Seal, inlet manifold (intake performance valve seals) Front wiper blades – 24" (jet/spoiler) + 18" (jet) for 2002.5MY onwards (no bonnet jets) Silicone grease ⏱️ Chapters: 00:00 Introduction 01:57 Scuttle removal 08:09 Check and Performance valves review 09:42 Check valve removed 10:24 Quick release of vacuum line (manifold end) 10:59 Comparing existing and replacement vacuum line 12:44 Upper intake performance valve 16:18 Lower intake performance valve 17:21 Fitting the replacement check valve 18:20 Fitting the vacuum line (manifold end) 19:12 Initial verification checks 20:09 Scuttle and wiper arms refitted 20:57 Post test-drive error code checking 21:55 DSC N/A error again! 22:34 Brake Booster Solenoid recalibration 24:34 Post test-drive again 25:45 Summary of issues and steps so far 28:31 Preparing to update the TCM 31:02 Starting the TCM reprogramming process 34:00 Re-checking the DTCs logged 35:00 Conclusion 35:10 Close ⚠️ Note / Disclaimer: Diagnostic and programming work carries risk. Always ensure stable voltage (battery support), correct vehicle selection, and follow best practice for your equipment. I’m sharing what worked on my car. 🔗 Project S-Type 3.0 Sport Playlist Catch up on the full Project S-Type series here: 👉    • Project S-Type   👍 If this helped, please like, subscribe, and drop a comment with how you got on. #Jaguar #JaguarSType #C1777 #DSCNotAvailable #ABS #CarDiagnostics #JaguarRepair #VacuumLeak #BrakeBooster #SDD #ZF6HP26 #TorqueConverter #TooOldClassics #ProjectJaguar #DIYAutoRepair