Powertrain, generic (extended)

P25F6 AIR System B

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P25F6 is the overall monitor for a second secondary air injection system, lettered B, on engines with two separately controlled air delivery paths; system A reports through P0410 and P0411. During warm-up after a cold start a pump pushes fresh air into the exhaust, so leftover HC and CO burn off and the catalyst lights off sooner. CARB wants the complete delivery chain monitored, every switching valve included, and with separate paths the flow to each bank. No manufacturer documents P25F6 publicly; Toyota's 4.7 L 2UZ-FE V8 shows such a layout with one switching valve per bank but stores mostly its own codes for it. P25F6 is the general fault of system B, P25F7 the narrower flow complaint. The driver sees the MIL and fails an emissions test, while the car normally drives as usual.

Likely causes

Secondary air pump of system B worn, seized or water-damaged
Switching or check valve of system B stuck, often after debris from the pump
Cracked, loose or disconnected air hose or vacuum line
Faulty pump relay, fuse or wiring of system B

Symptoms

  • MIL on, usually after a cold start
  • Secondary air readiness monitor not complete, emissions test failed
  • Unusual whining or no pump noise during the first minute after a cold start

Repair estimate

DifficultyMediumDIY possible
Parts and labour€80–900
Time0.5–3 h

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

Parts involved

air pump bair check valveair pipes

Related codes

P25F7P0410P0411P0415P0419

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