Two technicians are discussing stepper motor fuel gauges. Technician A says that a defective gauge can usually be repaired individually without replacing the entire cluster of panel gauges. Technician B says that if the power lead to the fuel tank sending unit is disconnected from the tank unit and grounded (ignition on), the fuel gauge should go to full. Which technician is correct?
A. Technician B only
B. Neither Technician A nor Technician B
C. Technician A only
D. Both Technician A and Technician B
The correct answer and explanation is:
The correct answer is A. Technician B only.
Explanation:
Technician A claims that a defective gauge can typically be repaired individually without replacing the entire cluster. This statement is not entirely accurate because many modern fuel gauges, particularly those integrated into digital or multi-function clusters, are difficult to repair individually. They often require specialized knowledge or tools, and in some cases, the entire cluster may need to be replaced for effective repair.
Technician B, on the other hand, is correct in their statement. In a typical automotive fuel gauge system, the fuel level sending unit sends a varying resistance signal to the gauge based on the fuel level. If the power lead to the sending unit is disconnected and grounded, the circuit will simulate a maximum resistance value. This causes the fuel gauge to show a full reading (maximum position), since the system interprets the grounded condition as the fuel level being at its highest.
Fuel gauge systems generally work by using resistance to determine the fuel level, and grounding the power lead bypasses the sending unit’s resistance signal, causing the gauge to read full. This behavior is a standard diagnostic procedure used by technicians to check for faults in the fuel gauge system, as it helps verify that the gauge itself is functioning correctly.
In summary, Technician B is correct because the method described is a standard test procedure for verifying fuel gauge functionality, while Technician A’s statement about repairability does not apply universally to all vehicles, especially modern ones.