Vehicle Exhaust PPM Checker
Failed emissions with high CO? That number diagnoses your engine: high CO means it is running rich — too much fuel, not enough air. Enter the reading for likely causes.
Calculator
Vehicle Exhaust PPM Checker
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Failed emissions with high CO? That number diagnoses your engine: high CO means it is running rich — too much fuel, not enough air. Enter the reading for likely causes.
How to use this calculator
- Enter exhaust CO PPM.
- See the diagnostic band.
- Get likely causes.
The formula
Bands based on typical gasoline exhaust CO levels.
What the units mean
PPM (parts per million) — one part of solute per million parts of the total mixture. The workhorse unit for trace concentrations in water, air, and food.
Worked example
Idle CO 3.5% (35,000 PPM) → very rich; check O2 sensor, fuel pressure, air filter.
Quick reference
| CO | Indication |
|---|---|
| <0.5% | Normal |
| 0.5–2% | Slightly rich |
| >2% | Rich — diagnose |
Gasoline idle, warmed up.
Where you will actually use this
The PPM number points at the fault before you buy parts.
- Emissions test prep
- Engine diagnostics
- Pre-purchase checks
Mistakes that give wrong answers
- Testing with a cold engine
- Ignoring exhaust leaks before the sensor
Key takeaways
- Formula: Exhaust CO bands for diagnostics
- Remember: Gasoline idle, warmed up.
- Watch out for: Testing with a cold engine
- Next step: run your own numbers in the calculator above, then verify with a measurement — calculated values are only as good as the inputs.
Frequently asked questions
What is normal exhaust CO?
Well under 1% (10,000 PPM) at idle for modern cars; lower is better.