P218F: Reductant No Flow Detected

What it means

The DEF dosing system commands flow but the pressure or flow sensor reports no actual delivery — typically a fully blocked dosing nozzle, a frozen line, or a dead pump.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

The reductant system pumps and meters DEF (AdBlue) through a line and dosing nozzle into the exhaust to reduce NOx emissions. The control module sets P218F when it commands delivery but detects no reductant flow, which can result from a blocked nozzle, a failed pump, or a frozen line.

Common causes

Most likely first.

1. Dosing line or nozzle fully blocked
2. Pump dead
3. Line frozen at very low ambient temperature

Symptoms

• Check engine light or NOx warning on
• AdBlue/DEF level or quality warning
• Possible no-start countdown after ignore period
• Failed emissions inspection (NOx)

How to diagnose it

1. Read freeze-frame data and scan for DEF level, quality, pressure, pump, and NOx-related codes to establish the conditions and related faults.
2. Check the DEF level and inspect the tank, lines, and dosing nozzle for visible leaks, damage, crystallized deposits, or blockage.
3. Consider ambient temperature and inspect accessible reductant lines for signs of freezing before attempting a flow test.
4. Use scan-tool data or the manufacturer's test procedure to check whether the pump builds pressure and whether flow is reported when dosing is commanded.
5. If pressure is available but no delivery is detected, inspect or test the dosing nozzle and line for restriction; if pressure is absent, test the pump and its electrical supply.

Common fixes

• Restore the DEF level if it is low and clear any related condition codes.
• Thaw a frozen line using the vehicle manufacturer's approved method and check for damage.
• Clean or replace a blocked dosing nozzle or restricted line as specified by the manufacturer.
• Repair the pump wiring or replace a failed reductant pump after confirming the fault.

Can I keep driving?

Avoid ignoring this fault: emissions warnings may be followed by a restart countdown or no-start restriction, and the vehicle may have reduced power. If a countdown is displayed, follow the vehicle's instructions and arrange repair promptly.