Blogger Coding Tips

Diagnostic Signal Path

The diagnostic signal path shows how the sensor or vehicle component sends information to the control module and how the ECM or PCM processes that information.

Sensor / Vehicle Component
↓
Signal Circuit
↓
ECM / PCM
↓
Signal Processing
↓
Fuel / Ignition / Vehicle Control

CAN Bus Waveform

A typical CAN network uses two complementary communication signals, CAN-H and CAN-L. During dominant communication, CAN-H rises while CAN-L falls.

Typical pattern: CAN-H and CAN-L move in opposite directions during dominant communication. The exact voltage levels and waveform characteristics depend on the vehicle and CAN network.

Oscilloscope Waveforms

An oscilloscope can help identify a normal signal, a low or weak signal, and an unstable or distorted signal. The actual voltage, frequency, duty cycle, and waveform shape must be compared with the manufacturer's specifications.

1. Normal Signal

Normal: The signal has a stable and repeatable amplitude, timing, and frequency.

2. Low Signal

Low: The waveform amplitude is lower than expected. Possible causes include sensor faults, wiring resistance, poor ground, low supply voltage, or circuit problems.

3. Distorted or Unstable Signal

Distorted: Irregular amplitude, timing, spikes, dropouts, or unstable transitions may indicate a sensor, wiring, grounding, electrical interference, or mechanical problem.

Important Diagnostic Note

These waveforms are simplified diagnostic illustrations. Actual voltage levels, frequency, duty cycle, timing, and waveform shape vary according to the vehicle, engine, sensor, control module, and manufacturer. Always compare oscilloscope measurements with the vehicle-specific service specifications.