LH 2.4 is one of Volvo's most widely used engine management systems (including 200, 700, and 900 series). The system has built-in diagnostics that are read from a black box located in the engine bay.

Open the diagnostic box located in the engine bay and remove its cover. Connect the box's dedicated wire to connector A2 (fuel system). Power the car (ignition on, engine off). Press the button briefly (approx. 1 second) and count the red LED flashes. The code is three digits. For example, flashes: pause - pause - means code 1-1-1.

Code Explanation 1-1-1 No fault. 1-1-2 Control unit defective. 1-1-3 Lambda sensor or mixture too rich/lean. 1-2-1 MAP sensor or MAF sensor (air flow meter) defective. 1-2-2 Intake air temperature sensor. 1-2-3 Engine temperature sensor. 1-3-1 Ignition system RPM sensor signal missing at start. 1-3-2 Battery voltage too high or low. 1-3-3 Idle signal from throttle switch missing. 1-4-1 Flywheel TDC sensor (Top Dead Center). 1-4-2 EZK ignition control unit failed. 1-4-3 Knock sensor signal missing or invalid. 1-5-4 EGR system flow too high. 2-1-2 Lambda sensor signal missing. 2-1-3 Full throttle signal from throttle switch missing. 2-1-4 RPM sensor signal intermittent. 2-2-1 Mixture too lean at part load. 2-2-3 Idle control valve signal missing. 2-2-4 Coolant temperature sensor signal disturbance. 2-3-1 / 2-3-2 Lambda value incorrect (lean/rich) at part load or idle. 2-4-1 EGR system flow too low. 2-4-4 Knock sensor signal invalid. 3-1-1 Speed sensor signal missing. 3-1-2 Knock sensor signal missing (mixture enrichment in knock). 3-1-3 Activated charcoal canister valve malfunction. 3-2-1 Cold start injector signal missing. 3-2-2 Air flow meter hot wire broken (meter defective).

Codes must be read at least once before clearing. Read all stored codes until the first code appears again. Press the button for at least 5 seconds, then release it. Wait for the LED light to turn on steadily. Press the button again for at least 5 seconds and release. The light should turn off. Verify success by pressing the button once briefly; the code should now be 1-1-1.

Codes must be read at least once before clearing. Read all stored codes until the first code appears again. Press the button for at least 5 seconds, then release it. Wait for the LED light to turn on steadily. Press the button again for at least 5 seconds and release. The light should turn off. Verify success by pressing the button once briefly; the code should now be 1-1-1.

These refer to the ignition system's RPM or TDC sensor (usually on the flywheel). If these signals are missing, the car will usually not start at all or stalls while driving. First clean the sensor connector and check the wiring before buying a new sensor.