You can usually drive in the short term, but diesel SCR faults often escalate to reduced power or a limited number of restarts, so have P2057 diagnosed and repaired promptly to avoid a derate or no-start. P2057 is a diesel emissions code meaning the reductant (DEF/AdBlue) injector control circuit for bank 2, unit 2 is reading low — the electrical circuit that meters diesel exhaust fluid into the SCR system is out of range on the low side. Diesel emissions faults like this often trigger warnings and, if ignored, a power derate or no-restart countdown.
What P2057 means
Modern diesels use a selective catalytic reduction (SCR) system that injects a metered dose of reductant — diesel exhaust fluid (DEF/AdBlue) — into the exhaust to cut NOx emissions. The dosing control module drives the reductant injector electrically and monitors that circuit. P2057 sets when the control circuit for the specified injector (bank 2, unit 2) reads low — a short to ground, an open with a low reading, or a driver that cannot hold the commanded level. Because emissions compliance is mandatory, diesel vehicles typically respond to reductant-system faults with warning lights and escalating measures such as reduced power or a limited number of restarts, so it should be addressed promptly. The usual causes are the injector, its wiring/connector or the dosing module.
Symptoms
- Check-engine light, often with an emissions/SCR or DEF warning
- Warning messages about exhaust-fluid system faults or limited restarts
- Reduced power (derate) if the fault is left unresolved
- Higher-than-normal DEF consumption or visible DEF residue at the injector
- Related reductant-dosing, NOx or SCR-efficiency codes stored with it
- Possible countdown-to-no-restart warnings on some diesel vehicles
Common causes
- Short to ground or chafed wiring in the reductant-injector control circuit
- Corroded, loose or heat-damaged injector connector
- Failed or clogged reductant (DEF) injector
- Fault in the reductant dosing control module
- DEF crystallization fouling the injector and circuit area
- Poor ground affecting the injector control circuit
Severity & driving advice
Severity: Moderate to high — Diesel emissions faults commonly escalate to power derate or restart limits, so prompt repair avoids being stranded.
Can I drive? You can usually drive in the short term, but diesel SCR faults often escalate to reduced power or a limited number of restarts, so have P2057 diagnosed and repaired promptly to avoid a derate or no-start.
Diagnostic approach
- Read codes and freeze-frame — Confirm P2057 and note any companion SCR/NOx or dosing codes and the conditions when it set.
- Inspect the injector wiring and connector — Check the bank 2, unit 2 reductant injector's harness and connector for chafing, corrosion, heat damage and DEF residue.
- Test the injector circuit — Measure the injector's resistance and the control-circuit continuity against specification to find a short, open or out-of-range value.
- Check for DEF crystallization/clogging — Inspect the injector tip and mounting for hardened DEF deposits that can foul the injector and disturb the circuit.
- Isolate injector vs. module — Confirm the dosing module is commanding the injector correctly before replacing the injector or the module.
Estimated repair costs
Typical US repair costs (parts & labour) for the faults behind P2057. These are national-average estimates, not a quote— your actual price varies by region, shop labour rate, and your vehicle’s make, model and year. Figures reviewed 2026.
| Repair | Estimated cost (USD) |
|---|---|
| Diagnosis (circuit + dosing test) | $90–$200 |
| Wiring / connector repair | $100–$400 |
| Reductant (DEF) injector replacement | $250–$700 |
| Reductant dosing control module | $350–$900 |
FAQ
Can I keep driving with P2057?
In the short term usually yes, but diesel emissions systems often escalate reductant faults to reduced power or a countdown of limited restarts, so it should be repaired promptly to avoid being stranded.
What is the reductant injector?
It is the electrically controlled injector that meters diesel exhaust fluid (DEF/AdBlue) into the exhaust for the SCR system that reduces NOx emissions; 'bank 2, unit 2' simply identifies which injector on multi-injector systems.
Could DEF crystals cause P2057?
Yes — hardened DEF deposits can foul the injector and the area around its connector, so inspecting the injector tip and connector for crystallization is part of the diagnosis.
Will P2057 fail an emissions test?
Very likely — an active SCR/reductant fault with the check-engine light on generally fails emissions testing, and it can also trigger the vehicle's own power-limiting measures.