Automobile & Light Truck Certification Test A5 BrakesAnti-lock Brake System (ABS) Diagnosis and RepairMedium
A vehicle exhibits an ABS warning light and a C0040 fault code, indicating 'Right Rear Wheel Speed Sensor Input Signal Malfunction'. Upon inspection, the technician finds that the sensor's resistance is within specifications, but the wiring harness shows signs of rodent damage near the sensor connector. What type of electrical fault is MOST likely present due to this damage?
- AAn open circuit in the wiring.
- BA short to ground in the circuit.
- CA short to power in the circuit.
- DHigh resistance in the circuit.
Show answer & explanationAnswer & explanation
Correct answer: D. High resistance in the circuit.
Rodent damage often involves chewing through insulation, which can expose wires and cause partial breaks or corrosion. While a complete break would be an open circuit, partial damage often leads to increased resistance in the circuit, which can manifest as an intermittent or incorrect signal.
Why the other options are wrong
- A. An open circuit means a complete break, leading to a 0 MPH reading. High resistance suggests a degraded but not fully broken connection, causing a 'malfunction' rather than a complete loss of signal.
- B. A short to ground would usually result in a constant low or zero voltage signal, potentially blowing a fuse if unprotected, which isn't the primary 'signal malfunction'.
- C. A short to power would typically cause a constant high voltage signal or blow a fuse, which doesn't fit the 'signal malfunction' description as well as high resistance.
Rodent Damage Electrical Faults
Damage to vehicle wiring caused by rodents, often leading to various electrical circuit issues.
- Commonly causes high resistance due to partial conductor damage or corrosion.
- Can also lead to open circuits (complete breaks) or shorts (to ground or power).
- Often results in intermittent or incorrect sensor signals and related DTCs.
Memory trick: Chewed wires can be a real fright, making resistance high or signal not right!