1997 Mercury Villager 3.0L V6 - P0325 and P0135 Codes: Chugging, O2 Sensor Failure & Coolant Reservoir Leak
Hello, I just returned from Advance Auto with check engine light diagnostics. The codes detected are P0325 (Cylinder 1 Knock Sensor Circuit Malfunction) and P0135 (Oxygen Sensor Heater Circuit Malfunction - Bank 1). My mother has noticed that the van exhibits a chugging sensation during acceleration—specifically, when I release the accelerator pedal, there's a delay of about 3 seconds before the engine responds. This occurred only once during my recent drive. Vehicle details: - 1997 Mercury Villager 3.0L V6 - 174,000 miles - Automatic transmission The van was purchased two years ago for a low price. Based on the engine bay appearance, no major repairs have been performed since then. I've only done routine oil and filter changes—though there is significant grime buildup around the oil filler cap area. I cleaned it recently, but residue returns over time. Additionally, the engine coolant reservoir consistently drains to empty. After filling it to the maximum line, it drops back to the bottom within a day. When I start the engine after refilling, small amounts of white smoke are visible from the exhaust. I'm seeking advice on possible root causes and whether these issues could be related to the fuel filter or other components. Edit: Photos have been attached for reference—please see them if available. Note: Is the fuel filter a likely culprit here? I suspect it might be, but I'd like confirmation before proceeding.
The fuel filter is a plausible suspect, especially given the age and mileage of your 1997 Mercury Villager. However, the chugging sensation you're experiencing is more likely related to distributor issues or faulty oxygen sensor performance in this model. Regarding P0325—this code often appears on older Nissan/Mercury V6 engines without causing immediate drivability problems. It may be a persistent reading rather than an active fault and doesn't always trigger the check engine light, especially when scanned with certain OBD-II tools. For P0135 (O2 sensor heater circuit), if one of the oxygen sensors is failing or has damaged wiring, it can generate this code. I recommend replacing the O2 sensor with a dealer-grade part to ensure compatibility and reliability. If you're considering replacing the distributor, choose only a reputable rebuild—this component is known to fail in older 3.0L V6 engines.