Jim Grant's Tech Tips

’97 01 VW Jetta, Oxygen Sensor Eate

Q: I own an ‘01 VW Jetta and I had the oxygen sensors replaced about 14 months ago. I have the same symptoms as before. I’m only getting 200 miles out of a tank full of gas, down from 325 miles out of a tank and the check engine light is on. Why is this continuing to happen? My luck is that it happened just after the 1 yr warranty expired. I’m wondering why this keeps happening????? Is there something else that needs to be repaired so this will not continue? I have 36,000 miles on my Jetta.

Sanders

A: The first step, have the computer checked for the codes it is reporting. There are nearly one hundred codes that can cause the check engine light to come on in your vehicle. (Many of which can cause a loss of gas mileage.) If the code is an oxygen sensor code and the sensor has failed again, yeah there is a question why? Bosch makes the oxygen sensors in your vehicle and Bosch is known in the automotive industry for making a very good product. That is why many other vehicle manufacturers use Bosch product in their vehicles. There was this Volvo that was ripping through oxygen sensors like there was no tomorrow. On the third go around it was decided that something else had to be going on, but the question was just what? To keep it to a short novel it was found that the coolant temperature sensor for the computer had shifted out of range, it wasn’t broken, it just wasn’t telling the truth. This little fib caused the computer to provide just a little too much fuel. The oxygen sensors could only handle this adjustment issue for so long before they would cloud up and turn the check engine light on. The computer, believing it was in control, would report oxygen sensor problems. A replacement coolant temperature sensor was the needed fix. Oxygen sensors do fail, but when it becomes a repeat failure you have to start looking in directions you just wouldn’t normally look in.