Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisHard
A vehicle is exhibiting symptoms of an intermittent short to voltage in a specific sensor circuit, causing erratic readings on the scan tool. Which of the following multimeter functions would be most effective for detecting this type of fault?
- ADC voltage measurement with the circuit energized.
- BResistance (Ohms) measurement with the circuit de-energized.
- CAC voltage measurement with the circuit energized.
- DContinuity test with the circuit de-energized.
Show answer & explanationAnswer & explanation
Correct answer: A. DC voltage measurement with the circuit energized.
A 'short to voltage' means the circuit is intermittently receiving voltage from an unintended source. To detect this, the circuit must be energized, and a DC voltage measurement will reveal if and when the unintended voltage appears. An intermittent fault requires monitoring the voltage over time or wiggling the harness to induce the fault while measuring.
Why the other options are wrong
- B. Resistance checks are for open circuits or high resistance, not shorts to voltage, and require the circuit to be de-energized.
- C. While AC voltage might be present in some sensor circuits, a 'short to voltage' typically refers to an unintended DC voltage source. Measuring DC voltage is more direct for this type of short.
- D. Continuity tests are for open circuits, not shorts to voltage, and require the circuit to be de-energized.
Short to Voltage
An electrical fault where a circuit or wire intermittently or continuously receives voltage from an unintended source, leading to incorrect signals or component operation.
- Circuit receives unintended voltage.
- Often causes erratic behavior.
- Requires live circuit testing.
Memory trick: Short to voltage: look for rogue power with a DC volt check.