BMW 5-Series O2 Sensor Issues & Failed Emissions Help

Hey! I had a similar issue with my 1998 BMW 3 series. I've got some experience working on cars, but I'm no expert. My check engine light came on and fuel consumption went through the roof. Took it to my regular workshop and they found a faulty connection in the O2 sensor wiring harness. The cable was damaged and causing incorrect readings. Total repair was 95 Euro, they replaced the connection and cleaned the sensor area. Before I can give more specific advice, could you share: Have you scanned for error codes? Is the engine running rough? Do you notice any unusual exhaust smell? This could help narrow down if you're dealing with the same problem I had.

Thanks for the detailed response! Just had my service done last week at 110639 KM. I did get it scanned at a parts store and got code P0135, pointing to the O2 sensor heater circuit. Engine runs okay but definitely burns more fuel than usual. No weird smells from the exhaust that I can tell. Your repair sounds way more affordable than what I was expecting. Good to know it might just be a wiring issue rather than needing a whole new sensor. I'll make sure to have them check the connections first. Did you notice an immediate improvement in fuel economy after the fix?

Hey again! Yeah, with that P0135 code you're describing pretty much exactly what I went through with my BMW. After they fixed the wiring connection on mine, the fuel consumption dropped back to normal within like 2-3 fill-ups. It was such a relief seeing those numbers go down again! Since you mentioned your car's running okay otherwise, it's probably similar to what I had, just the heater circuit acting up rather than the whole sensor being bad. The wiring fix on my 3 series worked perfectly and I haven't had any issues since (it's been about 8 months now). Just make sure to tell your mechanic about that specific code and ask them to thoroughly check the wiring harness and connections before replacing the whole sensor. Like you said, could save you some serious cash. My mechanic showed me the damaged wire after fixing it, it was just a tiny break in the insulation that was causing all that trouble! Quick tip from my experience, while they're in there, have them check all the O2 sensor connections. Better to catch any potential issues before they become problems. Keep me posted on what you find out!

Thanks so much for sharing your experience! I really appreciate you taking the time to explain everything in detail. Just got off the phone with my mechanic and booked the car in for tomorrow morning. I mentioned the P0135 code and asked them to check the wiring harness first, just like you suggested. They seemed to know exactly what I was talking about. It's such a relief to hear your repair was straightforward and that your fuel consumption went back to normal after fixing it. Hoping mine will be a similar case with just a wiring issue. The fact that you haven't had any problems for 8 months is really encouraging too. I'll definitely have them inspect all the O2 sensor connections while they're at it, that's a great tip. Will save me potential headaches down the road. Thanks again for all your help! I feel much more confident going into the repair now knowing what to expect.