Engine load (PID 04) explained

Calculated engine load (PID 04) is the ECU’s estimate of how much of the engine’s available air capacity is in use, as a percentage. Idle in Park is low. A highway grade in high gear is high — even if your foot is only halfway down.

Why freeze frame without load is half a story

The same P0171 at 12% load (idle, vacuum-leak territory) is a different job than P0171 at 75% load (fuel delivery, MAF, or exhaust leak under power). P0300 that set at 8% load vs 80% load changes whether you start with an idle vacuum test or a load misfire test. Always read load next to RPM and speed in freeze frame.

Typical shapes (gasoline, automatic, very approximate)

• Hot idle, Park: often under ~25%
• Gentle cruise: mid range
• Hard acceleration or a steep hill: high, approaching the top of the scale

Diesel and boosted engines will not match a naturally aspirated idle. Use your car as the baseline: record a known-good drive in MotorBit, then compare when the light comes on.

Load vs throttle vs MAF

Throttle is the pedal / plate. MAF is air mass. Load is the calculated result. A clogged converter can show high load and poor acceleration with modest throttle — power is being spent pushing exhaust. A vacuum leak can show odd load vs MAF at idle. Graph all three when the complaint is shake on acceleration or a catalyst code.

In MotorBit

Keep load on the dashboard. When a code sets, open freeze frame and ask: was this an idle number or a work number? That single question stops a lot of wrong parts.