GMC Terrain O2 Sensor Issues Spike Fuel Consumption

I dealt with a very similar issue on my 2011 GMC Acadia last year. Having some experience with basic car maintenance, I first noticed similar symptoms, the malfunction indicator light came on and fuel efficiency dropped significantly. After the initial sensor testing at my local workshop, they found a loose connection in the exhaust system wiring. The oxygen sensor itself was functioning correctly, but the cable connection had deteriorated over time, causing irregular air-fuel ratio readings. The total repair cost was 95 Euro, which covered diagnostic testing and fixing the faulty wiring connection. The check engine light cleared up right after the repair, and fuel consumption returned to normal levels within the next few tank fills. To better assist with your specific case, could you share: Current mileage on your Terrain, Whether the check engine light is solid or flashing, The specific error codes you retrieved from scanning, Any unusual sounds from the exhaust system, The approximate percentage increase in fuel consumption These details would help determine if your issue matches what I experienced or if it might be something different.

I had my last service just 2 weeks ago at 117187 KM. The check engine light keeps showing a steady glow, not flashing. My OBD scanner showed P0141 and P0135 codes. No unusual sounds coming from the exhaust system, but fuel consumption increased by roughly 25%. The oxygen sensor reads appear inconsistent, which matches with the car components behavior others described. From what I understand, these symptoms strongly point to the vehicle emissions system requiring attention, particularly the O2 sensor circuit.

Thanks for providing those details. Based on the error codes P0141 and P0135, your situation actually appears more straightforward than what I encountered with my Acadia. These codes specifically indicate oxygen sensor heater circuit issues, which is different from the wiring connection problem I initially had. With a 25% increase in fuel consumption and those specific codes, this strongly suggests a failed oxygen sensor heater rather than just a loose connection. The fact that your vehicle emissions system is showing these symptoms shortly after service suggests the issue likely developed gradually and wasn't caught during routine maintenance. In my case, after fixing the initial wiring, I actually ended up replacing the oxygen sensor six months later when similar symptoms returned. The full sensor replacement cost 180 Euro including labor. The repair completely resolved the increased fuel consumption and prevented potential damage to the catalytic converter. For your Terrain, given the clear error codes and symptoms, I recommend going straight for the oxygen sensor replacement rather than attempting intermediate fixes. The consistent sensor readings you mentioned are a telltale sign of a faulty sensor that needs replacement, not just repair.

Based on those details, I now understand my issue better. The P0141 and P0135 codes are more specific than I initially thought, pointing directly to the heater element in the oxygen sensor rather than a general wiring issue. Since the check engine light remains steady and fuel consumption has jumped 25%, replacing the sensor seems like the logical next step. The cost estimate of 180 Euro for parts and labor sounds reasonable, especially considering the potential savings in fuel consumption once fixed. My symptoms match the classic signs of a faulty sensor, inconsistent readings and increased fuel usage. I appreciate learning that delaying the repair could risk damaging other car components like the catalytic converter. I will schedule the oxygen sensor replacement soon, rather than waste time with partial fixes. This has been really helpful in confirming my initial suspicion about the sensor circuit being the root cause. Good to know others have successfully resolved similar issues with a straightforward sensor replacement.