Relative Compression Test
A relative compression test compares compression between cylinders using starter current.
What is Relative Compression Test?
It is quick and needs no plug removal. Scan tools or oscilloscopes perform it. It shows differences, not absolute values. A cylinder with low compression causes a lower current peak, so it stands out in the pattern. It is a good first check before removing spark plugs or glow plugs.
How it works
Starter current rises on each compression stroke.
Why it matters for your car
Disable fuel injection during the test. Confirm results with a compression test.
Other terms
- Acoustic Vehicle Alerting System (AVAS)
- Airbag Warning Light (SRS Light)
- All-wheel Drive (AWD)
- Badge (Emblem)
- Coolant Flush (Coolant Change)
- Exhaust Hanger (Exhaust Mount)
- Final Drive
- Gear Ratio
- Low Washer Fluid Warning
- Lowering Springs
- Night Driving
- Paint Blistering (Rust Bubbles)
- Paint Colour Matching
- Quarter Lights (Vent Windows)
- Remote Engine Start
- Silicone Spray
- Snow Foam
- Structural Adhesive (Body Bonding)
- Tachometer (Rev Counter)
- Vehicle Recall