What Causes the Fuel Consumption Display to Fluctuate Erratically?

[AliviaMarie]

Fluctuations in the car's fuel consumption display are primarily caused by significant changes in external temperature or when the vehicle's water temperature stabilizes. Under the influence of external factors, the computer-calculated fuel injection volume may vary considerably, leading to erratic jumps in the average fuel consumption gauge. Occasional minor fluctuations in the average fuel consumption are normal. However, if the fluctuations persist for an extended period, it is advisable to seek maintenance and inspection, as this situation may be caused by a fault in the car's dashboard wiring. Causes and Diagnostic Methods for Fuel Gauge Malfunctions: Fuel gauge issues: Malfunctions in the car's fuel gauge itself can cause the gauge to remain static or display inaccurately. The diagnostic method involves observing whether the fuel gauge needle fails to move approximately half a minute after turning on the ignition switch, or if it moves erratically or displays inaccurate measurements. Sensor malfunction: A faulty car sensor can cause the fuel gauge to remain static. The diagnostic method involves using a multimeter to measure the resistance of the fuel sensor's variable resistor by clamping the probes to its two terminals in R×1Ω mode. If the reading deviates from the standard value, the sensor is faulty. Dashboard coil short circuit: A short circuit in the car's dashboard coil can cause fuel gauge malfunctions. The diagnostic method involves measuring the voltage using a multimeter.

[PeterRose]

I've experienced erratic fuel consumption display before, mainly caused by normal fluctuations in instantaneous fuel consumption. When accelerating, the fuel injection volume increases instantly, causing the displayed consumption to spike; when coasting in gear with the throttle released, the system stops fuel injection, making the reading suddenly drop to zero. Especially in urban areas with frequent starts and stops, the numbers dance around like crazy. Additionally, minor sensor issues can contribute to the problem, such as a stuck fuel level float or carbon buildup on the oxygen sensor, leading to unstable signals. I recommend trying a highway drive first—if the display stabilizes at a constant speed, it's fine. If it still jumps around, the sensors need checking. Using quality gasoline regularly can help reduce such annoyances.

[SanHolden]

I've looked into the causes of this issue, and the key lies in the signal acquisition process. The vehicle's computer calculates instantaneous fuel consumption based on data from the fuel flow meter and vehicle speed sensor, with values refreshing every few seconds. If the wheel speed sensor gets clogged with mud or the fuel flow meter is obstructed by debris, the signals will become erratic. Aging wiring causing poor contact is another common reason - loose connectors can make the data appear intermittently. Another possibility is unstable battery voltage interfering with sensor operation. You can try cleaning mud deposits near the wheel speed sensor and tightening the battery terminals yourself. If the abnormality persists for several consecutive days, it's best to visit a dealership to read the diagnostic trouble codes.

[JessicaLee]

This issue depends on the difference between average fuel consumption and instantaneous fuel consumption. Instantaneous fuel consumption naturally fluctuates dramatically—for example, spiking to 15L/100km when going uphill and dropping to 2L when going downhill, which is completely normal. However, if the average fuel consumption (long-term memory) also jumps erratically, that's unusual. Common causes include unstable fuel system pressure; a clogged fuel pump filter can cause inconsistent fuel injection. A faulty crankshaft position sensor can also make the computer miscalculate fuel consumption data. I recommend trying to reset the ECU by disconnecting the negative battery terminal for five minutes and then reconnecting it. Cleaning the throttle body can also improve signal accuracy, as carbon buildup affects air intake measurements.