P2059 — Reductant Injection Air Pump Control Circuit/Open #

Note: The wording of this code may vary depending on the vehicle manufacturer.

• Reductant Injection Air Pump Control Circuit/Open (Generic/SAE)
• Reducing Agent Injection Air Pump Control Circuit/Open (BMW, Mercedes-Benz)
• DEF Air Pump Control Circuit/Open (Ford, GM, FCA/Stellantis)
• AdBlue Injection Air Pump Control Circuit/Open (Volkswagen/Audi)

Summary of DTC P2059 #

DTC P2059 signals a detected fault in the electrical circuit controlling the reductant injection air pump. This pump is a key component in Selective Catalytic Reduction (SCR) systems, often found on modern diesel engines. Its role is to deliver air to aid the injection of reductant fluid (such as DEF — Diesel Exhaust Fluid, also called AdBlue) into the exhaust stream. When the control circuit is open or not operating within design parameters, the Engine Control Module (ECM) sets this code. The result can be incomplete reduction of nitrogen oxides (NOx), leading to emissions system inefficiency and possible warning lights.

Frequent Symptoms for Code P2059 #

Symptoms for P2059 can range from subtle to obvious, depending on the vehicle and the extent of the circuit failure. Drivers may notice changes in vehicle performance or only see a warning on the dashboard. Common signs include:

• Check Engine Light (MIL) illuminated
• Possible reduced engine power or limp mode in severe cases
• Increased exhaust emissions (may not be directly noticeable without inspection)
• Warning messages related to SCR, DEF, or emissions system malfunction
• Possible delayed or failed DEF dosing events

Probable Causes for P2059 (in order of likelihood) #

Most cases of P2059 are electrical in nature, but mechanical faults are possible. Here’s what typically triggers this code, listed from most to least common:

1. Open or damaged wiring/connectors in the air pump control circuit
2. Failed reductant injection air pump (internal electrical fault or open winding)
3. Faulty or corroded relay (if equipped, controls power to the pump)
4. Blown fuse in the air pump circuit
5. Defective Engine Control Module (ECM) (rare)

Step-by-Step Diagnosis for P2059 #

A methodical approach is essential to confirm the root cause of P2059. Use basic tools (digital multimeter, scan tool) and always follow safety protocols. Here’s a proven troubleshooting workflow:

• 1. Confirm the code with a scan tool. Record freeze-frame data for context.
• 2. Visually inspect air pump wiring and connectors for damage, corrosion, or disconnection.
• 3. Check fuses and relays associated with the air pump circuit. Replace as needed.
• 4. Test the air pump for continuity and resistance (compare with OEM specs); bench test if possible.
• 5. Verify power and ground at the pump connector while actuating the circuit (using scan tool or manually).
• 6. Check circuit continuity between ECM and pump; repair any open circuits.
• 7. Clear the code and retest system operation after each repair step.

Possible Repairs for P2059 #

Once the faulty component or connection is identified, address it with the appropriate corrective action. The most common repairs include:

• Repair or replace damaged wiring or connectors in the air pump circuit
• Replace the reductant injection air pump if it fails continuity or bench test
• Replace a faulty relay or blown fuse
• Reprogram or replace the ECM (only if all other causes are eliminated and verified with OEM diagnostics)

Is It Safe to Drive with Code P2059? #

Limited — It is generally safe to drive your vehicle with a P2059 code for short distances, provided there are no driveability issues and only the warning light is present. However, prolonged operation can lead to increased emissions, potential legal issues (failed inspections), and eventual triggering of limp mode if the DEF system becomes inoperative. Prompt diagnosis and repair are highly recommended to avoid costly repairs and compliance problems.

Vehicles Most Commonly Affected by P2059 #

While P2059 may be seen on many diesel vehicles equipped with an SCR system, it tends to appear more often on certain models and manufacturers, including:

• Ford Super Duty trucks (Power Stroke diesel)
• GM Silverado/Sierra HD (Duramax diesel)
• Ram 2500/3500 (Cummins diesel)
• Mercedes-Benz Sprinter (BlueTEC diesel)
• Volkswagen/Audi TDI vehicles
• BMW X5/X7 and 3-series/5-series diesels

Common Mistakes & Best Practices with P2059 #

Avoiding misdiagnosis and unnecessary parts replacement is key. Here are frequent pitfalls and tips for accurate repair:

• Assuming the air pump itself is always faulty — check wiring and relays first
• Overlooking corroded or loose connectors, especially in harsh climates
• Neglecting to clear codes and retest after repair, which can mask intermittent issues
• Skipping OEM service bulletins or wiring diagrams for your specific vehicle
• Not verifying the repair with a test drive and emissions system readiness check

Express FAQ about P2059 #

Q: Will P2059 cause my vehicle to fail a state emissions test?
A: Yes, in most regions, an active P2059 code will trigger a check engine light and cause your vehicle to fail OBD-II emissions testing until properly repaired and the code is cleared.

Q: Can a bad DEF fluid or low tank cause P2059?
A: No, P2059 is specifically related to the air pump control circuit, not DEF fluid quality or level. However, unresolved air pump issues can eventually impact overall SCR system function.