Powertrain, generic (extended)

P25F7 AIR System B Incorrect Flow Detected

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

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

Symptoms

  • MIL on after one or two cold starts
  • Emissions test failed or readiness incomplete
  • Driveability normally unchanged

Repair estimate

DifficultyMediumDIY possible
Parts and labour€80–1,000
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

air pump bair check valvesecondary air switching valve

Related codes

P25F6P0411P0410P0415P0419

References: law.cornell.edu, static.nhtsa.gov, en.wikipedia.org.