The compression test is a comparative test and shows if any cylinder deviates from the others. The purpose of the test is to be a tool when troubleshooting the engine.
For the test result to be correct, make sure that the following points are followed during the whole test.
Test conditions:
Coolant temperature above 30 °C.
Erase any fault codes.
Turn off the engine.
Ignition on.
The compressed air system shall be filled so that the compressor does not charge.
Clutch and brake pedals not activated.
Any retarder, white smoke limiter, and exhaust brake shall be off.
Battery voltage above 20V.
Parking brake applied.
Procedure:
Start the function.
Crank the engine using the start key until the bar in the dialogue box is filled.
A dialogue box appears and says to turn off and on the voltage 2 times with the start key.
Repeat the above twice until the whole test is done, all the time the instructions will be shown in the dialogue box.
If the test does not continue despite the voltage being turned off and on twice, then voltage feed to the control unit must be cut off, e.g., by removing and installing fuse number 19.
The function is done.
If the function fails, check the test conditions and repair any faults.