Sec Air Inj Sys Air Flow/Press Sensor Circ Range/Perf Bank1


The PCM has detected a problem in the secondary air injection system air flow or pressure sensor circuit. The secondary air injection system uses ambient air, which is pumped into the engine exhaust, to reduce emissions. “Bank 1” denotes the bank of the engine which contains the number one cylinder. Consult the manufacturer’s service manual (or the equivalent) for the location of the number one cylinder.

Code Set Parameters

Variations in secondary air injection system pressure and flow are read by the PCM in increments of input voltage. Input readings that vary from the manufacturer’s referenced amount by greater than 10-percent are likely to cause a code to be stored and a malfunction indicator lamp to be illuminated. Some models require multiple ignition cycles (or drive cycles) for a malfunction indicator lamp to be illuminated but a code should be stored on the initial failure.


Symptoms may include abnormal noises from the secondary air injection system, engine hesitation upon acceleration, the engine may stall at startup or idle, a stored code, and (eventually) an illuminated malfunction indicator lamp.

Common Causes

The most common causes of this code being stored occur in cold weather conditions. The secondary air injection pump is protected by using a one way check valve that is integrated into the air inlet hose. The check valve usually goes bad and allows condensation (water) from the exhaust to enter the pump, where it freezes in extremely cold weather. With ice inside of the secondary air injection pump, it binds and either causes catastrophic pump failure or overloads the circuit (usually blowing the fuse). Electrical wiring and connectors are also subject to being burnt by high temperature engine exhaust.

Common Misdiagnosis

Secondary air injection pump replacement, without fabricating a water drain on the pump housing, may lead to repeated pump failure. Testing the one way check valves is also critical to making a thorough diagnosis.


  • The secondary air injection system uses either a belt driven or electric pump inject ambient air into the engine exhaust system for the purposes of emission reduction
  • Heat resistant silicon based hoses are used to supply the pump with cooler (than engine exhaust) ambient air
  • Filtered air is typically drawn in through the air filter housing, though some models utilize a remote filter housing designed exclusively for the secondary air injection system
  • The cooler air is then pumped into the exhaust system via high temp silicon and steel lines attached to ports in the exhaust down pipes
  • One way check valves are fitted into each exhaust hose to prevent condensation from entering the pump and causing a malfunction
  • These valves fail regularly
  • Engines that are designed using a “V” configuration usually require dual inlet ports in the exhaust pipes and dual one way check valves. Test check valves by attempting to blow air through them from both directions
  • The check valve should allow air to flow through in only a single direction
  • If air will flow through the valve in either direction, then the one way check valve is bad and should be replaced
  • Failure to replace faulty one way check valves can result in repeated secondary air injection pump failure, due to contaminants entering the replacement pump. Certain tools will be virtually indispensible when performing a successful diagnosis of this code storing condition
  • They are a scanner (or code reader) and a digital volt/ohmmeter. Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
  • Continue your diagnosis by visually inspecting all secondary air injection system hoses and fittings for signs cracking, breaking, or heat damage from engine exhaust and repair as necessary
  • Inspect all electrical wiring and connectors for corrosion or damage from hot exhaust gases
  • Repair as required and retest
  • Check system fuses (see manufacturer service manual for fuse location and size) and replace blown fuses as needed
  • After fuses are replaced, operate the secondary air injection system to see if the fuse blows again
  • If the fuse continues to blow, suspect pump failure but electrical shorts are also a possibility
  • Typically, water from the exhaust system will damage the secondary air pump, causing the pump to deteriorate and seize often blowing the fuse in the process
  • This is the most likely cause of this code and it occurs mainly in cold weather.