Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisMedium
A technician is diagnosing an intermittent short to voltage in a specific sensor circuit. The vehicle's wiring diagram shows that the sensor signal wire runs through a main engine harness that also contains wires for the fuel injectors and ignition coils. Which of the following is the MOST likely cause of the intermittent short to voltage?
- AA damaged ground wire for the sensor.
- BAn open circuit within the sensor itself.
- CExcessive resistance in the sensor's signal wire.
- DA short between the sensor signal wire and a power wire from a different circuit within the harness.
Show answer & explanationAnswer & explanation
Correct answer: D. A short between the sensor signal wire and a power wire from a different circuit within the harness.
A 'short to voltage' means the circuit is intermittently receiving voltage when it shouldn't, often from an unintended source. If the signal wire is sharing a harness with other power-carrying wires (like those for injectors or ignition coils), insulation damage can cause the signal wire to occasionally contact and pick up voltage from one of these adjacent power wires.
Why the other options are wrong
- A. A damaged ground would typically cause an open or a short to ground, not a short to voltage.
- B. An open circuit would result in no signal, not an intermittent voltage spike.
- C. Excessive resistance would affect signal strength or cause a voltage drop, not an intermittent short to voltage.
Short to Voltage
An electrical fault where a wire or circuit unintentionally comes into contact with a voltage source, causing an incorrect voltage reading or component operation.
- Often due to damaged insulation.
- Can be intermittent or constant.
- Causes unintended circuit activation or incorrect sensor readings.
Memory trick: Voltage where it shouldn't be, means a wire's touching, can't you see?