Questions and Answers

Jeep Cherokee Trip Computer Q. My 2002 Jeep Cherokee is under warranty. The trip computer is inaccurate. Over a tank of fuel, it will typically indicate 15.3 MPG, when it in fact gets 17.9 MPG. The latter reading based on the old fashioned mileage test method of filling the tank, traveling a known distance and then refilling the tank. The calculation is then done using the calculated fuel amount used.

The average mileage displayed by the trip computer is always less than the actual, over the same distance. The odometer reading on the dash measures the same as that on the trip computer, therefore I would assume it is a problem based on the fuel usage measurement or the calculations of the computer.

The dealer insists everything is okay, and that it is not meant to be any more accurate than it is. But I have seen many other makes that are perfect. The dealer tested the resistance of the fuel level sender unit in the tank, and said that the resistance is "within spec".

The question I ask is, how can this possibly conclude a non faulty sending unit? If the resistance range of that item was, hypothetically, 10 to 50 ohms, and their reading was 20 ohms.

This proves nothing. 20 ohms at what level? How do they know the rest of the resistance range is existent, accurate and linear? How can they know what levels the rest of the resistance range represent, and if the changes are proportional? Or that the float isn't damaged, etc?

I say they can't. What do you think, and what do you think might be the problem?

Thanks very much,
Scott

A. The resistance readings are approximate values. There are a lot of variables involved in checking a sending unit of any kind. One major variable is how much fuel is in the tank. You can't tell exactly how much fuel there is so the best you can do is be within specs.

As for trip computers, don't rely on them for much. There is only one time when they are completely accurate, when the vehicle is in PARKat an idle. The other time it is fairly accurate is when you are at speed with the cruise control on.

Other than that they are just a toy added on to make the vehicle more appealing to the buyer. If you relay on them for "Fuel Consumed", "Average MPG" and "Miles Till Empty", at some point you'll be walking.