What it means
Reductant Injection Valve Circuit Low (Bank 2 Unit 1): the signal voltage is below the expected range. This valve doses reductant (DEF/AdBlue) into the exhaust for SCR NOx reduction.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The Bank 2 Unit 1 reductant injection valve doses DEF/AdBlue into the exhaust when commanded by the SCR control module. P2051 sets when the valve circuit signal is lower than expected, which can result from a short to ground, poor terminal contact, or a failed valve circuit.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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
- Review freeze-frame data and confirm the Bank 2 Unit 1 valve circuit reads low during a supported command or actuator test.
- Inspect that injector's connector and harness for chafing, corrosion, moisture, loose pins, or a wire contacting ground.
- Check the valve control and supply circuits for a short to ground and test connector voltage and continuity against the manufacturer's specification.
- Measure the valve winding as directed by service information and compare it with specification to identify an internally shorted or failed valve.
- If the valve and wiring pass, test the control module driver circuit before considering module replacement.
- Repair the confirmed fault, then repeat the actuator test and check for normal circuit behavior.
Common fixes
- Clean and secure corroded or loose Bank 2 Unit 1 connector terminals where appropriate.
- Repair chafed wiring or a valve circuit wire shorted to ground.
- Replace the Bank 2 Unit 1 injector if its winding fails the specified test.
- Repair a confirmed module driver fault and verify the circuit under command.
Can I keep driving?
A short drive may be possible if the vehicle runs normally, but have the fault diagnosed promptly and heed any SCR countdown. Continued driving can reduce NOx treatment and may eventually prevent restarting.
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.