AC600

What the code means

Code AC600 indicates insufficient efficiency of the selective catalytic reduction (SCR) system. The SCR system reduces nitrogen oxide (NOx) emissions by injecting AdBlue (urea) solution into the exhaust stream. When efficiency is low, the system can't achieve the required NOx neutralization rate. Possible causes: a faulty NOx sensor, a clogged AdBlue injector, or SCR catalytic converter degradation.

Symptoms

• Dash indicators: Check Engine Light, AdBlue system warning
• Engine behavior: possible power loss (limp mode)
• Emissions: elevated NOx levels

Diagnosis and repair

Step 1: Check the NOx sensor

Using diagnostic equipment (ISTA/INPA), read the NOx sensor readings before and after the SCR catalytic converter. Compare against reference values.

Step 2: Inspect the AdBlue system

Check the AdBlue injector for clogs, check the pump and fluid level. Clean or replace the injector if needed.

Step 3: Test the SCR catalytic converter

Assess converter efficiency from the diagnostic data. If the converter has degraded, replace it.

Step 4: Replace faulty components

Replace faulty sensors, injectors, or the catalytic converter. After the repair, clear the codes and run a system regeneration if required.

Secondary problems

Ignoring the fault can lead to:

• Diesel particulate filter (DPF) clogging from the wrong temperature and gas-composition balance
• Increased exhaust backpressure
• Poorer engine response and a shift into limp mode
• Accelerated wear of exhaust system components