P25F7: AIR System B Incorrect Flow Detected

What it means

AIR System B flow is detected as incorrect. The code does not specify whether flow is too high or too low, or identify its cause.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

This code means the detected airflow through AIR System B does not match what the vehicle expects when that system operates. The code does not say whether flow is too high or too low; a partly blocked pipe, weak pump impeller, or leak between the pump and check valve can all alter flow.

Common causes

Most likely first.

1. Air pipe partially blocked by carbon
2. Worn pump impeller reduces flow
3. Leak between pump and check valve

Symptoms

• Check-engine light may illuminate
• Reduced engine performance

How to diagnose it

1. Record freeze-frame data and check live data or scan-tool test results for AIR System B to determine when its flow was judged incorrect.
2. Inspect the System B pipe between the pump and check valve for leaks, loose joints, carbon blockage, or crushed sections.
3. Check the pump impeller and motor operation by commanding the pump on as allowed by the manufacturer's procedure and listening for weak or abnormal operation.
4. Inspect the System B check valve for sticking, soot buildup, or leakage that could affect measured flow.
5. If no visible fault is found, measure System B pump output and check for flow restriction using the manufacturer's method.

Common fixes

• Seal a leak between the AIR System B pump and check valve.
• Clear carbon from a partially blocked System B air pipe or replace a damaged section.
• Replace a worn AIR System B pump impeller or failed pump assembly.
• Repair or replace a sticking or leaking System B check valve.

Can I keep driving?

The fault primarily affects emissions control, though reduced performance may occur. Limit driving if power loss makes the vehicle difficult to control in traffic, and avoid prolonged use if engine operation worsens.