VW Lupo Diesel Starting Failure: Wiring vs Battery Fix

Had similar symptoms on my VW Polo 1.9 TDI (2004). The slow cranking initially pointed to a battery issue, but after testing revealed the charging system was not working properly. The main problem turned out to be a combination of a worn starter motor and deteriorated wiring harness connections. The voltage drop test showed significant power loss between the battery and starter. The wiring harness had corroded terminals where it connects to the starter motor, causing resistance in the circuit. The fix required: Replacing the starter motor, Installing new wiring harness sections, Cleaning all ground connections, Testing the circuit breaker function This was a serious repair as the charging system components are interconnected. Poor connections can cause a cascade of electrical issues. Worth noting that on these VW diesels, the starter motor works harder than on petrol engines due to higher compression, so wiring integrity is crucial. Would strongly recommend getting the charging system fully tested before replacing parts. A proper voltage drop test across all major connections will pinpoint exactly where power is being lost in the circuit.

Thanks for sharing your experience. My Lupo had exactly these symptoms last winter. After reading your detailed response, I wonder if my case was also related to the wiring harness deterioration, as the mechanic only replaced the starter motor without checking the electrical connections thoroughly. The ignition switch was also tested but came back fine. In the end, they found multiple issues with the charging circuit that needed attention. Would you mind sharing what the total repair cost was in your case? Also curious if youve had any other electrical faults pop up since the fix? My fuse box has been acting up recently and Im wondering if its connected to the earlier problems.

The starter motor electrical issues turned out to be connected to the Terminal 30 continuous plus problem. Once the mechanic did a complete diagnosis, they found the battery was heavily discharged, causing multiple electrical faults in the system. The power supply issues were affecting several components. The repair involved replacing the battery and fixing corroded connections in the wiring harness near the starter motor. Total cost came to 290€, which included full testing of the charging system and cleaning all ground points. Since fixing the Terminal 30 continuous plus connection and installing the new battery, the electrical system has been working perfectly. No short circuit issues or ignition switch problems have occurred. The fuse box symptoms you mentioned could definitely be related, unstable power supply can cause various electrical gremlins throughout the system. For peace of mind, get a full voltage drop test done across the charging circuit. Poor connections can hide in unexpected places and cause intermittent starting problems even with a new battery installed.

After trying multiple fixes myself, I finally took the car to a reputable electrical specialist. The mechanic did a complete diagnostic check of the charging system and found multiple issues beyond just the starter motor problems I initially suspected. They discovered significant voltage drops across several connection points and a partially corroded wiring harness near the fuse box. The continuous positive connection was indeed failing, causing unstable power delivery to the starter motor. The total repair ended up costing 450€, which included: New wiring harness sections, Replacement of corroded terminals, Full circuit breaker testing, Labor for complete electrical diagnosis Its been 3 months since the repair and the car starts perfectly every time. No more slow cranking or electrical gremlins. Looking back, I should have gone straight to an electrical specialist rather than trying basic fixes. The ignition switch and all other systems are working as they should now. Really glad I got it properly diagnosed and fixed rather than just replacing parts. These old VWs need proper attention to their electrical systems to keep running reliably.