With P25F7 the engine controller finds that the air delivered by secondary air system B does not match its expectation while the system is switched on after a cold start. Depending on the design, it judges the flow from how the oxygen sensors on that side react, from a pressure sensor in the air line or from pump behaviour. For 2006 and later vehicles outside LEV III, CARB demands detection before reduced flow pushes emissions beyond one and a half times the relevant FTP limit; LEV III vehicles use the threshold table instead, and with separate paths each bank counts on its own. No manufacturer documents P25F7 publicly. On Toyota's 2UZ-FE V8, a bulletin blames debris passing through the pump and fouling the valves for comparable faults. P0411 is the matching code for system A, P25F6 the general fault of system B.
Low severity. Can I keep driving?Yes, you can keep driving, though it should be repaired: the car pollutes more at startup and may not pass an inspection.
Symptoms
- MIL on after one or two cold starts
- Emissions test failed or readiness incomplete
- Driveability normally unchanged
Most likely causes
- Air pump of system B delivers too little air
- Switching or check valve fouled or stuck partly closed
- Air passages to the exhaust restricted by carbon deposits
- Leaking air hose so that part of the flow escapes
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P25F7 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 5: Speed and idle
- F7: Specific fault in that system
Frequently asked questions
Can I keep driving with code P25F7?
Yes, you can keep driving, though it should be repaired: the car pollutes more at startup and may not pass an inspection.
What causes code P25F7?
The most common causes are: air pump of system B delivers too little air; switching or check valve fouled or stuck partly closed; air passages to the exhaust restricted by carbon deposits.
Related codes
- P25F6AIR System B
- P0411AIR System A Incorrect Flow Detected
- P0410AIR System A
- P0415AIR System Switching Valve B Circuit
- P0419AIR System Control B Circuit
Sources
- law.cornell.edu: 13 CCR 1968.2
- static.nhtsa.gov: SB 10075945 0699
- en.wikipedia.org: Secondary air injection
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.