TORKO

P0491 Secondary air injection system insufficient flow (bank 1)

What P0491 means

After a cold start the engine control unit runs the secondary air pump and expects the bank 1 oxygen sensor to show a lean exhaust. It did not see enough change, so it concludes that too little air is reaching bank 1.

P0491 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.

At a glance

Severity
Medium
Typical repair cost
100–800 €
Workshop time
0.7–3 h
Repair difficulty
Medium
DIY possible
Yes
Check engine light
Yes
Affects emissions test
Yes

Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.

Symptoms

Common causes

  1. Weak or failed secondary air pump
  2. Stuck closed combination/check valve
  3. Carbon-blocked air passages in the cylinder head
  4. Cracked or disconnected air hose
  5. Faulty pump relay or valve control solenoid

Can I keep driving with P0491?

You can keep driving, but have it checked within one to two weeks. It mainly affects emissions and catalyst warm-up.

What to check first

  1. Listen for the pump after a cold start and check air flow at the pump outlet
  2. Inspect hoses and the check valve for cracks, leaks or soot
  3. Test the pump relay and vacuum control solenoid
  4. Clean blocked passages or replace the pump or valve

Related codes

Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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