P2259 — Secondary Air Injection System Control “B” Circuit Low #

Note: The code label may vary depending on the vehicle manufacturer.

• P2259: Secondary Air Injection System Control “B” Circuit Low (Generic/SAE)
• P2259: Secondary Air Injection System Control “B” Circuit Low (Toyota, Lexus)
• P2259: Air Injection Pump Control “B” Circuit Low (Ford, GM, Honda)

Summary of DTC P2259 #

The P2259 diagnostic trouble code (DTC) is triggered when the engine control module (ECM) or powertrain control module (PCM) detects a low voltage or resistance condition in the Secondary Air Injection System Control “B” Circuit. The secondary air injection (SAI) system is designed to reduce harmful emissions by injecting fresh air into the exhaust stream during cold starts, helping the catalytic converter reach operating temperature faster. The “B” circuit typically refers to a specific control side—such as the relay, solenoid, or air pump motor—within the system, as labeled by the OEM. A “low” signal means the ECM sees less voltage or current than expected, which can compromise emission control effectiveness. If this code is present, the vehicle may fail emissions testing and experience related performance issues.

Common Symptoms for DTC P2259 #

A vehicle with a stored P2259 code may exhibit subtle or no symptoms, especially in mild climates or with short drive cycles. However, some drivers or technicians may notice one or more of the following:

• Check Engine Light (CEL) illuminated
• Failed emissions test (especially due to elevated cold-start emissions)
• Rough idle or hesitation during cold startup
• Reduced engine performance or slight hesitation
• Increased exhaust odor during cold start
• Possible air pump or relay noise (if the component is stuck or failing)

Probable Causes for DTC P2259 #

Causes for P2259 generally relate to failures in the control circuit, power supply, or the air injection components themselves. The most frequent causes, in order, include:

1. Faulty secondary air injection pump relay or control solenoid
2. Open or shorted wiring harness in the SAI “B” circuit
3. Blown fuse related to the air injection system
4. Malfunctioning air injection pump (motor failure, internal short)
5. Corroded or poor electrical connections (especially at relay or pump)
6. Faulty ECM/PCM (rare, but possible if all else checks out)

Step-by-Step Diagnostic for DTC P2259 #

To accurately diagnose P2259, follow a methodical approach to avoid unnecessary part replacement and confirm the root cause:

• 1. Scan for additional codes: Address any related air injection or circuit codes first.
• 2. Inspect the air injection system fuse: Replace if blown and recheck for code reset.
• 3. Examine wiring and connectors: Look for corrosion, loose pins, or damaged insulation on the SAI “B” circuit from the relay, pump, and ECM.
• 4. Test relay operation: Use a multimeter to confirm relay clicks and provides proper voltage/output when commanded.
• 5. Check pump operation: Apply 12V directly (if safe) to verify pump function and listen for unusual noises or lack of operation.
• 6. Inspect ECM/PCM outputs: With a wiring diagram, test for correct control signals at the ECM output pin.
• 7. Clear the code and perform cold start tests: Confirm that repairs are effective and code does not return.

Possible Repairs for DTC P2259 #

Repairs will depend on the pinpointed cause after diagnosis. Always address the most common issues first, as listed below:

• Replace faulty secondary air injection pump relay or solenoid
• Repair or replace damaged wiring/connectors in the SAI “B” circuit
• Replace blown or undersized fuse for the air injection system
• Replace air injection pump if defective or inoperative
• Clean or secure corroded electrical connections
• Replace ECM/PCM only after confirming all other components are functional

Is It Safe to Drive with Code P2259? #

In most cases, driving is limited but not immediately unsafe. The P2259 code does not usually affect critical engine or braking functions, but it does mean your vehicle will emit higher pollutants during cold starts and may fail an emissions test. Long-term driving without repair can lead to premature catalytic converter aging or clogging. If you notice rough running or performance issues, limit driving and address the problem promptly.

Vehicles Most Commonly Affected by DTC P2259 #

While P2259 is a generic OBD-II code, it is most often seen in certain OEM systems using advanced air injection or relay-based controls, including:

• Toyota (Camry, Highlander, Tundra, Tacoma, 4Runner, Lexus RX/GS/IS)
• Honda and Acura (Pilot, Odyssey, Accord, MDX)
• General Motors (Chevrolet Silverado, GMC Sierra, Cadillac Escalade)
• Ford (F-150, Expedition, Explorer, Mustang)
• Volkswagen/Audi (Passat, Jetta, A4, Q5)

Common Mistakes & Best Practices for DTC P2259 #

Avoiding misdiagnosis saves time and money. The most frequent pitfalls and pro tips include:

• Replacing the air injection pump without checking fuses, relays, and wiring
• Overlooking corroded connectors, especially in humid or winter climates
• Assuming the ECM/PCM is faulty before confirming all other components
• Not performing a cold start test after repairs to confirm the fix
• Neglecting OEM wiring diagrams and test procedures

Quick FAQ for DTC P2259 #

Q: Will clearing the code fix my air injection issue?
A: No. Clearing the code will temporarily turn off the Check Engine Light, but the underlying problem in the SAI “B” circuit must be addressed or the code will return.

Q: Can a weak battery cause code P2259?
A: Rarely. A weak battery can cause low voltage codes, but P2259 usually points to specific issues in the air injection control circuit rather than general power supply problems.