Home›Trouble Codes›P2051

P2051 — Reductant Injection Valve Circuit Low Bank 2 Unit 1

Manufacturer-specificPowertrain (engine & transmission)

P2051 means the powertrain control module has detected a low-voltage or excessive resistance condition in the circuit that controls the Selective Catalytic Reduction (SCR) reductant injector (DEF dosing valve) for Bank 2, Unit 1. In plain terms, the injector is not receiving or returning the expected electrical signal, so the controller cannot command DEF injection properly. This usually turns on the check engine light and can disable SCR dosing.

Symptoms

What causes it — most likely first

1. Faulty reductant injection valve (DEF injector)

The injector solenoid can develop an internal open, short-to-ground, or high resistance, causing the PCM to see a low circuit voltage. This is the most common cause.

2. Wiring harness damage or chafing

The power, ground, or control wires between the injector and the reductant control module/PCM can be rubbed through, pinched, or broken, creating a short-to-ground or open circuit.

3. Corroded or loose injector connector

Moisture, salt, or poor pin contact at the injector or module connector can increase resistance or drop circuit voltage below the expected range.

4. Faulty reductant control / DEF dosing module

If the vehicle uses a separate reductant control module, its internal driver or output stage can fail and produce a low-side circuit fault, though this is less common than the injector or wiring.

5. PCM injector driver failure

The PCM output that commands the injector can rarely fail, but this should not be assumed unless the injector, wiring, and any intermediate module have been ruled out.

How it's diagnosed

  1. Visually inspect the reductant injector and its connector for corrosion, contamination, bent pins, and damaged wiring, especially near heat shields or exhaust components.
  2. Disconnect the injector and measure its coil resistance; compare the reading to the manufacturer specification and check for a short to ground or an open circuit.
  3. Check the injector power and control circuits with a scan tool bidirectional command or lab scope to confirm the PCM/module is sending the expected voltage and the circuit is not shorted low.
  4. Perform a continuity and isolation test of the wiring harness between the injector and the reductant control module/PCM to locate opens, shorts, or high-resistance sections.
  5. If the injector, wiring, and connectors are good, test or substitute the reductant control module where applicable; consider PCM driver testing only after everything else is eliminated.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationManufacturer-specific (P1/B1/C1/U1)
Related codesP2049 — Reductant Injection Valve Circuit HighP2050 — Reductant Injection Valve Circuitopen P2052 — Reductant Injection Valve Circuit HighP2053 — Reductant Injection Valve Circuitopen P2054 — Reductant Injection Valve Circuit Low P2055 — Reductant Injection Valve Circuit High

Frequently asked

Can I keep driving with P2051?

Short trips are usually possible, but prolonged driving may trigger emissions derate or limp mode and will cause the SCR system to stop dosing DEF, increasing NOx emissions.

Should I replace the PCM for P2051?

Usually no. The failed component is most often the reductant injector, its connector, or the wiring. PCM driver failure is uncommon and should only be considered after the injector, harness, and any reductant control module have been thoroughly tested.

Do I need to replace the whole DEF injector assembly?

If resistance tests and command tests show the injector coil is open, shorted, or stuck, replacement of the injector is typically required; the harness and connector should be inspected at the same time.

Can a contaminated DEF injector cause a circuit-low code?

Crystallized DEF can clog or corrode the injector and connector, increasing resistance or damaging the solenoid. Cleaning may help if caught early, but a damaged injector usually needs replacement.