1999 Jaguar XJ8 Vanden Plas: P1637, P1642, P1000 Fault Codes - Diagnosis & Repair Guidance
1999 Jaguar XJ8 Vanden Plas, 4.0L V8 engine, 99,500 miles. I recently performed a coolant flush and completed several repairs: - Replaced the fuel pump - Installed a new thermostat - Replaced the thermostat housing (aluminum) Additionally, I identified a leak in the Mass Air Flow (MAF) boot, which was temporarily sealed using tape. The car now exhibits an intermittent 'restricted performance' warning light that appears only about once every five starts. The issue resolves after a few minutes of driving. I have also observed voltage fluctuations affecting the dashboard LCD screen—specifically, the mileage display dims and brightens intermittently every few seconds. Furthermore, one of my rear brake lights will occasionally activate when starting the vehicle and remain on until I turn off the car; upon subsequent starts, it may fail to function consistently. I have been monitoring these symptoms alongside the following OBD-II fault codes: P1637 – CAN Link ECM/ABSCM Circuit/Network Malfunction P1642 – Fuel Pump Monitor Circuit High Input P1000 – OBD-II Monitor Testing Incomplete These codes may be related to recent work, particularly the fuel pump installation. Possible causes include damaged wiring harnesses or improper connections. I recommend checking all relevant fuses. The P1000 code typically clears after a normal drive cycle (a full driving session), but persistent dimming and brightening of dashboard lights suggest potential issues with the battery, corroded or loose connections in the starter or charging system, or a faulty alternator/regulated power supply. I advise having the battery, alternator, and associated wiring inspected. I am seeking advice on next steps to resolve these codes and intermittent performance issues.
Were these fault codes present before the recent repairs? P1637 indicates a CAN bus network malfunction between the ECM and ABSCM. P1642 points to a high input signal in the fuel pump monitor circuit—this could be related to improper installation or damaged wiring during the fuel pump replacement. Check all relevant fuses and connections. If the codes appeared after work, it's likely due to faulty harness routing or poor grounding. I recommend returning to the repair shop for a thorough inspection of the wiring and connections. P1000 indicates an incomplete OBD-II diagnostic cycle—this usually resolves with normal driving (a drive cycle). However, intermittent dashboard dimming suggests potential battery issues, loose connections in the charging system (starter or alternator), or a failing alternator/regulated voltage supply. A full inspection of the battery, alternator, and associated wiring is strongly advised. Good luck—please update us on your findings.