Key-on engine-off (KOEO) shows 2.3-2.5V representing barometric pressure at sea level. At warm idle, voltage drops to 0.9-1.3V reflecting intake vacuum of 16-20 inHg. Under turbo boost, voltage rises smoothly to 4.2-4.6V representing 14-18 PSI boost pressure. Signal must be rock-steady with less than 30mV noise and respond instantly to throttle changes.

At idle, MAF outputs 0.9-1.3V corresponding to 2-4 g/s airflow on naturally aspirated mode. Under acceleration and boost, voltage rises smoothly to 3.5-4.5V (peak airflow 80-120 g/s under full boost). Signal should be extremely clean with less than 50mV ripple, responding immediately to throttle changes with no lag or hesitation.

Initial peak inductive spike to 80-100V during solenoid opening (peak and hold driver circuit), followed by hold phase at ~14V battery voltage for injector pulse duration of 0.8-2.5ms at idle. Sharp cutoff spike to -80 to -100V when ECM cuts ground circuit, followed by 2-3 clean damped oscillations returning to baseline. Pulse width increases under load and boost.

Sharp voltage spike to 300-400V when ECM cuts primary current, followed by 3-5 clean oscillations decreasing in amplitude. Dwell time increases with RPM, typically 2-4ms at idle. Clean baseline at battery voltage between firing events with no noise or hash.

Initial firing line peaks at 8-15kV under normal conditions, immediate drop to relatively flat burn voltage of 2-4kV lasting 1-1.5ms. After spark extinction, 4-6 clean oscillations decreasing in amplitude. Burn time consistent across all cylinders within 0.3ms variance.

Post-catalyst O2 sensor shows minimal activity compared to upstream sensor, hovering around 0.6-0.8V with very slow, lazy transitions (2-3 second response time). If catalyst is healthy, this sensor should show flattened waveform with very small oscillations. During fuel cut on deceleration, voltage should drop to 0.1-0.2V and slowly rise back. Rapid switching similar to upstream sensor indicates failed catalyst.

Air-fuel ratio sensor maintains stable voltage around 3.0V during closed-loop operation at idle with very small oscillations (±0.1V). During acceleration enrichment, voltage smoothly rises to 3.5-4.0V, then returns to 3.0V. During deceleration fuel cut, voltage drops to 1.5-2.0V indicating lean condition. Response time to commanded changes should be under 100ms with no lag or sluggish behavior.

Clean digital square wave cycling between 0.2V and 4.8V at half the frequency of the crankshaft sensor (12.5Hz at idle). The pattern shows 4 distinct pulses of varying widths per camshaft revolution used for cylinder identification. With VTC (Variable Timing Control) active, pulse timing will shift relative to crankshaft sensor but maintain clean transitions.

Clean square wave transitioning sharply between near 0V (0.2V) and near 5V (4.8V) with consistent frequency at idle around 25Hz (1500 RPM). The missing tooth gap should show approximately 3x normal tooth spacing and occur once per crankshaft revolution. Rise and fall times should be less than 5 microseconds with no ringing or oscillation.

Two smooth, linear voltage ramps that move in opposite directions as throttle opens. At idle (closed throttle), TPS1 reads 0.5-0.7V while TPS2 reads 4.3-4.5V. At wide open throttle, TPS1 reaches 4.3-4.5V and TPS2 drops to 0.5-0.7V. Both signals should be clean without noise, glitches, or flat spots and maintain inverse relationship with combined voltage near 5V at all positions.

Clean square wave transitions between 0V and 5V with sharp rising and falling edges. At 5 mph expect approximately 6-8 Hz, at 30 mph expect 40-50 Hz. All four sensors should show identical frequency when driving straight at constant speed. Duty cycle should remain near 50% across all speeds.

Clean 0-5V square wave with crisp transitions. At 20 mph expect approximately 30-35 Hz, at 60 mph expect 130-140 Hz. Signal should be present whenever vehicle is moving and proportional to speed. Note: 2018-2024 Accord primarily uses calculated VSS from ABS sensors; transmission output sensor serves as backup verification.

Cold engine (68°F) should read 2.3-2.7V. Normal operating temperature (195-205°F) reads 0.4-0.7V. Voltage should transition smoothly during warm-up over 5-8 minutes with no sudden jumps or dropouts. ECM uses this for fuel enrichment, cooling fan control, and turbo boost mapping.

At ambient temperature (68-77°F) should read 2.0-3.0V. Under boost conditions temperature rises and voltage drops to 1.2-1.8V. During cold starts below 32°F, expect 3.5-4.0V. Signal should be stable with gradual changes only, no rapid fluctuations.

2018 Honda Accord Waveform References

Airflow Sensors

Fuel System

Ignition System

Oxygen Sensors

Position Sensors

Speed Sensors

Temperature Sensors