Powertrain, generic · Auxiliary emission controls

P0411 AIR System A Incorrect Flow Detected

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

After a cold start the secondary air (AIR) pump blows fresh air behind the exhaust valves so that unburnt fuel burns off and the catalyst heats up faster; a shut-off valve opens the path and stops exhaust from flowing back. P0411 means the measured air flow does not match the expected value. Passive systems judge it from the oxygen sensor or fuel control (Saab 900: less than 12 points of correction within 12 s). GM measures actively with a pressure sensor between pump and valve and compares it with a model while pump and valve are on – from 2018 a deviation above 5.0 kPa or below −4.9 kPa sets the code, MIL after two trips. The test needs a cold engine after a long stop, so short warm trips do not complete it.

Likely causes

Pump weak or failed (water, filter debris)
Combination valve partly stuck or check valve faulty
Hoses blocked, leaking or off; ducts in the head carboned up
Pressure sensor port blocked or sensor drifting (pressure-sensor systems)
Pump relay or supply with contact resistance

Symptoms

  • Check engine light on
  • Secondary air readiness not set (emission test)
  • Pump silent after a cold start, or unusually loud
  • Driving normal, higher cold-start emissions

Repair estimate

DifficultyMediumDIY possible
Parts and labour€80–1,000
Time0.5–3.5 h

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

What to check first

  1. Inspect hoses
  2. Test check valve
  3. Check pump output

Parts involved

secondary air pumpair combination valveair pressure sensorair hoses

Related codes

P0410P0491P0492P2431P2440P2444

References: gsi.ext.gm.com, gsi.ext.gm.com, saabwisonline.com, saabwisonline.com.