Smart Forfour Oil Warning: Sensor vs. Real Problem

Had a similar issue with a Smart Forfour diesel from 2006. As someone with some hands-on experience working on cars, I understand your concern about the oil pressure warnings. The symptoms you describe match exactly what happened with my car, multiple warning lights and inconsistent oil gauge readings. The oil temp sensor started acting up, triggering various warning lights. Initially worried it was a serious oil pressure problem, but it turned out to be a bad connection at the engine temperature sensor plug. Took it to my regular workshop where they diagnosed a faulty wiring connection to the oil sensor. The repair involved replacing some corroded wiring and reconnecting the temp sensor properly. Total cost was 95€ including diagnostic work and fixing the connection. To provide more specific advice about your situation, could you share: Current mileage on your car, When you last changed the oil, Whether the warnings appear right at startup or after driving, If you notice any unusual engine sounds, Whether oil level is correct when checked manually The combination of oil sensor and engine temperature readings can tell us a lot about whats really going on. Worth checking these basics before assuming worst-case scenarios.

Currently at 156841KM with last service done 3 months ago. The car diagnostics showed multiple error codes related to the oil pressure system. The readings from both the oil temperature sensor and oil pressure sensor fluctuate wildly while driving. Your experience matches my symptoms perfectly. Good to hear it was just a sensor connection issue rather than actual mechanical problems. Already checked the oil level manually and its spot on, plus no unusual engine noises or performance issues. The warning lights do come on immediately at startup and stay lit. Based on your feedback, will have the automotive sensor connections inspected first before considering full sensor replacement. The car temperature gauge also shows inconsistent readings, which further points to possible electrical issues. Will update the thread once I get it checked at the workshop. Thanks for sharing the repair costs too, helps set expectations.

After getting your update, I wanted to mention that my Forfour actually showed similar symptoms when checking the error codes. The fluctuating readings from both the oil temp sensor and pressure sensor turned out to be connected to the same wiring harness issue. Since your mileage is close to what mine was when this happened (I was at 162000KM), its likely facing the same wear and tear on the electrical connections. The fact that your temperature gauge also shows inconsistent readings strongly suggests a common electrical problem affecting multiple sensors. The immediate warning lights at startup without any engine performance issues matches the sensor fault pattern. In my case, after fixing the wiring connection to the oil temperature sensor, all gauges returned to normal readings and the error codes cleared completely. A quick tip from my repair experience: have them check the connector pins for corrosion, especially around the temp sensor area. The workshop found the pins had developed some resistance over time, causing those erratic sensor readings. Total repair time was about 2 hours, and they cleaned all sensor connections while the car was up on the lift. The whole harness didnt need replacement in my case, just proper cleaning and reseating of the connections fixed the issue.

Based on the conversation flow, here's my closing reply as: Thanks for the detailed follow-up about the sensor connections. Getting those matching symptoms and specific repair details really helps confirm my suspicions about the electrical issues. The car diagnostics system keeps showing those oil pressure related codes, but knowing your repair experience with the wiring harness at similar mileage gives me a clear direction. Really appreciate the tip about checking the connector pins near the temperature sensor. Will definitely have the workshop look at the connection resistance issues you mentioned. The fact that your oil gauge and engine temperature readings normalized after fixing the connections is exactly what I'm hoping for. Booked the car in for next week. Asked them specifically to inspect the sensor wiring and connections before jumping to full sensor replacement. The quoted diagnostic fee is 85€ which seems reasonable given your total repair costs. Will post back here once they find the root cause. Hoping its just corroded connections causing these oil temperature and pressure sensor readings to go crazy rather than anything mechanical.