P2EAD: Reductant Metering Unit 2 Performance

What it means

The reductant metering unit 2 does not deliver the expected DEF/AdBlue dosing within the calibrated profile. Pump aging or pressure regulator drift.

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

Reductant metering unit 2 supplies and controls the amount of diesel exhaust fluid (DEF/AdBlue) delivered for emissions treatment. The control system sets this code when unit 2 cannot deliver the expected dose within its calibrated profile, including when pump output has weakened or its pressure regulator has drifted.

Common causes

Most likely first.

1. Pump output degraded
2. Pressure regulator drifted

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. Record freeze-frame data and scan for related reductant, NOx, and dosing codes before clearing anything.
2. Check the DEF/AdBlue level and condition, and inspect unit 2, its lines, and connectors for leaks, crystallised deposits, or visible damage.
3. Use scan-tool live data or tests to compare commanded dosing or pressure with the response from metering unit 2.
4. Check the unit 2 electrical supply, ground, and connections, then inspect for restrictions in its delivery path.
5. If the basic checks pass, test pump output and pressure-regulator response using the manufacturer's procedures and specification.

Common fixes

• Correct a low DEF/AdBlue level or replace contaminated fluid with fluid meeting the vehicle specification.
• Clean external DEF crystallisation and repair a leaking or restricted unit 2 line.
• Repair a poor electrical connection or damaged wiring to metering unit 2.
• Replace the pressure regulator or metering unit 2 pump if testing confirms its output is out of specification.

Can I keep driving?

The vehicle may continue to run, but NOx emissions can rise and an emissions warning or no-start countdown may follow. Avoid delaying diagnosis, and follow any countdown instructions because the vehicle may eventually restrict starting.