Avenger O2 Sensor Failure Tanks Fuel Economy

I had a very similar issue with my 2006 Caliber diesel last year. With some experience working on cars, I initially thought it might be a major issue, but it turned out to be quite straightforward. The symptoms matched yours exactly, check engine light and poor fuel efficiency. The air-fuel ratio was completely off, which explained the increased fuel consumption. After running diagnostics, it pointed to the oxygen sensor, but the actual problem was just a loose connection. The mechanic found a damaged wire and connector going to the sensor. No need for a full sensor replacement, they repaired the connection and properly secured the wiring. Total cost was 95€ including diagnostic time. The repair immediately improved fuel efficiency and the check engine light cleared. Before jumping to conclusions about needing a new oxygen sensor, you should have the wiring and connections checked first. A faulty connection can mimic a bad sensor and trigger similar diagnostic codes. What diagnostic code are you getting specifically? Also, have you noticed any other symptoms like rough idling or black exhaust smoke? This information would help determine if your issue matches what I experienced with my vehicle. Just make sure to address this soon, as running with incorrect air-fuel mixture can potentially damage your catalytic converter over time.

Thanks for sharing your experience. The diagnostic code I am getting is P0136. My car has been serviced regularly, with the last maintenance done at 132000 KM. The check engine light appeared suddenly and the exhaust sensor issue seems to be affecting overall car maintenance costs through increased fuel consumption. I am not seeing any black smoke, but there is a slight rough idle when the engine is cold. The O2 sensor problems you mentioned with your Caliber seem quite similar to what I am experiencing. I will have the wiring checked before replacing any parts. The mechanic did mention taking extra care with the connections during the diagnostic check to rule out a simple fix like in your case.

Thanks for providing those additional details. Since you mentioned your mileage and maintenance history, it's worth noting that even with regular service, O2 sensors typically need replacement around 100000-150000 KM on these models. Your P0136 code specifically relates to the downstream oxygen sensor circuit, which is different from my initial wiring issue. Given your mileage and symptoms, especially the cold idle roughness, this points more toward a degraded sensor rather than just a connection problem like I had. The exhaust sensor is likely not reading properly, causing the engine computer to run a richer air-fuel ratio than necessary. This explains your increased fuel consumption. In my case, after fixing the wiring, I saw about a 15% improvement in fuel economy. However, with your symptoms and that specific code, you might be looking at a full sensor replacement. The automotive sensor itself costs around 120€, plus labor. While more expensive than my wiring fix, it's still a straightforward repair that should resolve both the check engine light and fuel consumption issues. Would suggest getting this addressed soon since the exhaust system relies on accurate O2 sensor readings to maintain optimal performance. Have you noticed if the fuel consumption increase happened gradually or suddenly?

The check engine light symptoms started suddenly, but thinking back, I realize the fuel efficiency decline was more gradual over the past few weeks. Your insight about the P0136 code and downstream O2 sensor makes a lot of sense. The mileage on my car definitely puts it in that replacement window you mentioned. The cold idle issue has gotten slightly worse since my last post, which supports your point about the sensor degrading rather than just having connection problems. I called my regular shop and got quoted 280€ total for the oxygen sensor replacement including labor, which seems reasonable based on the prices you mentioned. They can check the wiring during installation, but agreed the diagnostic code and symptoms point to a failing sensor. Going to schedule the repair for next week. Really hoping to see that 15% fuel efficiency improvement you experienced. The current fuel consumption is definitely hurting my wallet, and I want to prevent any potential damage to the catalytic converter by running too rich for too long.