You can drive, but do not put it off
Knocking under load
Under acceleration or on a hill the engine makes a metallic rattle, as if small change were being shaken. It goes away at steady throttle.
You can usually get home or to a garage, but every day of delay adds to the bill.
What to look at in the live data
- Ignition timing: a unit that hears knock pulls it back — and that shows in the data before the rattle gets loud.
- Knock sensor codes: if it does not respond, the unit plays safe all the time and the car feels flat.
- Fuel trims: a lean mixture knocks more readily.
- Temperature: overheating and knock travel together.
Common causes, cheapest first
- Low-octane fuel from the last fill-up — settled by one tank from a station you trust.
- Carbon deposits in the combustion chamber.
- The knock sensor or its torque: it is bolted to the block and lies if tightened wrongly.
- Overheating or a lean mixture.
Codes that show up with this
P0325Knock sensor circuit malfunctionP0326Knock sensor (bank 1) — signal out of rangeP0171System too lean (bank 1) — air leak or not enough fuelP0217Engine overheating
These parameters in the reference
Lamps that may be on
Do it step by step
One two-minute experiment halves a dozen possible causes — and costs nothing.How to find an air leak using fuel trims
A symptom is not a diagnosis. The same sign comes from a dozen different causes — the readings are what tell them apart, not the feeling.
How the app helps
CarScan shows exactly these readings live, remembers the highest and the lowest value of the trip, and puts them into a report you can hand to a mechanic.