A technician is diagnosing an intermittent issue where a vehicle's ABS warning light illuminates. The scan tool shows a C0035 (Front Left Wheel Speed Sensor Circuit Malfunction) code. A review of the wiring diagram shows the sensor is a two-wire inductive type. Using an oscilloscope, the technician measures the output of the front left wheel speed sensor while rotating the wheel manually. The waveform shows a consistent, low-amplitude sine wave with no dropouts. What is the MOST likely cause of the C0035 code given this information?
- AAn open circuit in the wheel speed sensor wiring.
- BA damaged wheel speed sensor tone ring.
- CA short to ground in the wheel speed sensor circuit.
- DA faulty ABS control module input circuit.
Show answer & explanationAnswer & explanation
Correct answer: D. A faulty ABS control module input circuit.
An inductive wheel speed sensor should produce an AC sine wave when the wheel rotates. If the oscilloscope shows a consistent sine wave (even low amplitude), it indicates the sensor itself, its wiring (no open or short), and the tone ring are likely intact and functioning mechanically. Therefore, if the ABS module is still reporting a circuit malfunction, the issue is most likely with the module's ability to correctly interpret or receive that signal, pointing to a faulty ABS control module input circuit.
Why the other options are wrong
- A. An open circuit would result in no signal or an erratic signal, not a consistent sine wave.
- B. A damaged tone ring would cause an inconsistent or distorted sine wave, or dropouts, not a consistent one.
- C. A short to ground would likely result in a flat line or a severely distorted signal, not a consistent sine wave.
Inductive Wheel Speed Sensor Waveform Interpretation
Analyzing the AC sine wave output of an inductive wheel speed sensor using an oscilloscope to diagnose sensor, tone ring, or circuit integrity issues.
- Produces an AC sine wave, amplitude increases with speed.
- Consistent sine wave indicates good sensor and tone ring.
- Dropouts, inconsistencies, or no signal indicate sensor, tone ring, or wiring problems.
- If sensor output is good but module reports fault, suspect module input.
Memory trick: Sensor's wave is fine, but the module whines; the input's the key, set the module free.