What it means
The reductant metering unit temperature sensor signal is intermittent or erratic.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant metering unit temperature sensor reports the temperature at the DEF dosing unit to the emissions control module. The module sets P20B0 when that signal jumps, drops out, or varies implausibly, often as vibration disrupts an intermittent connection.
Common causes
Most likely first.
- Intermittent connector
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
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
- Save freeze-frame data and watch the metering unit temperature reading on a scan tool while the fault is present to see whether it drops out or jumps.
- With the ignition off, inspect the metering unit sensor connector for looseness, corrosion, damaged seals, or terminals pushed back in the housing.
- Check the sensor harness where it passes near vibrating parts for rubbing, strain, or a loose retaining clip.
- Gently move the connector and harness while monitoring the live temperature reading to try to reproduce the interruption.
- If the fault remains, test sensor and harness continuity while flexing the wiring, and compare results with the manufacturer's specification.
Common fixes
- Reseat and secure the metering unit temperature sensor connector.
- Clean or repair corroded or loose connector terminals.
- Reroute and secure harness sections that rub against vibrating components.
- Repair damaged wiring or replace the sensor if its signal remains erratic with sound wiring.
Can I keep driving?
The vehicle may remain drivable, but the warning can progress to a DEF-related no-start countdown and emissions performance may be affected. Avoid putting off diagnosis, especially if a countdown appears.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.