2005-06 Secondary Air Injection (SAI) Systems

SAI System Operation

The Secondary Air Injection (SAI) is an emission control sub-system that normally operates upon initial cold or warm engine start-ups. The AIR pump supplies pressurized fresh air into the exhaust system to accelerate catalyst operation. This reduces HC and CO emission levels.

Early SAI systems used a large continually running mechanical pump driven by an accessory belt (a power robbing device) with noisy, vacuum-powered control switching.

The latest SAI system uses a small maintenance-free electric motor that runs for approximately 20 - 30 seconds with a whispering hum.

The AIR pump (fig. 7) is calibrated to operate when the engine start-up coolant temperature is between 41° F (5° C) and 122° F (50° C) and the ambient air temperature is between 41° F (5° C) and 140° F (60° C).

TIP: To avoid damage from frozen moisture in the system, the AIR pump will not run when the ambient air temperature is below 41° F (5° C).

When the engine is at operating temperature and the catalyst is warm enough to operate efficiently, the AIR pump is not required.

Features of the New Pressure Based SAI system

Components of the SAI system are familiar, with the exception of the new pressure sensor. The operation of the pressure sensor is similar to that of a Fuel Tank Pressure (FTP) sensor.

Earlier SAI systems used the HO2S sensor for diagnosis and verification of SAI system operation.

The new generation of SAI has a pressure sensor built into the electronic shut-off valve, which creates a more precise way to determine what is happening in the system. The Engine Control Module (ECM) detects abnormal conditions like a pump that is running continuously, or a shut-off valve that is stuck open.

Here are some additional changes to the AIR pressure based diagnostic system.

The pump inlet hose is routed to the air cleaner housing. This location allows the engine air filter to supply clean air and eliminates water intrusion into the AIR pump.

The in-rush current of the AIR pump is approximately 120 amps. During continuous operation, the current draw is 20 to 25 amps. In a high current circuit like this, resistance as low as 2 to 3 ohms anywhere in the pump circuitry may adversely affect pump operation.

The New Electronic Shut-Off Valve

The electronic control shut-off valve (fig. 8 and 9) (also known as the AIR control solenoid valve/pressure sensor assembly or check valve assembly) contains:

- A pressure sensor, for monitoring airflow pressure

- A control valve that allows pressurized air from the pump to flow to the exhaust manifold

- An electrical solenoid that operates the control valve

- A check valve that keeps exhaust gases from damaging the assembly and the rest of the system

The valve has no removable parts. The solenoid, check valve, and pressure sensor are serviced as an assembly (fig. 10).

A New 5-pin connector

B Electronic solenoid

C Pressure sensor

D Inlet

E Outlet to exhaust manifold

The highly robust shut-off valve opens reliably when commanded ON by the ECM. Conditions such as low manifold vacuum, high altitude, or heavy acceleration have no adverse effects on the operation of the valve. The ECM supplies the AIR pressure sensor with the following circuits:

- 5-volt reference

- Low reference ground

- A signal circuit that provides the control module with a voltage relative to internal AIR pressure changes.

The AIR solenoid has the following circuits:

- A voltage circuit supplied by the AIR solenoid relay

- A ground circuit

The ECM also supplies the AIR pump and AIR valve relays with separate control (ground) circuits.

The ECM compares measured AIR pressure values with predicted values to detect faults with:

- The AIR pump

- The AIR control solenoid valve/pressure sensor assembly

- The system hoses and pipes

- The AIR pressure sensor and relay control circuits.

Diagnosis

There are 3 phases of the SAI diagnostic:

- Phase 1 -- The ECM commands both the AIR pump and AIR check valve relays ON.

- Phase 2 -- The ECM continues to command the AIR pump relay ON and also commands the AIR valve relay OFF.

- Phase 3 -- The ECM commands both the AIR pump and AIR check valve relays OFF.

The increased number of DTCs now associated with SAI will help easily diagnose and repair the fault in the system. The following DTCs set when an AIR system fault is detected:

TIP: The P2444 diagnostic code is a type A. All of the others are type B, which illuminate the MIL on the second drive trip.

- DTC P0411 -- During Phase 1, an AIR system insufficient airflow condition has been detected due to a malfunctioning:

- AIR Check Valve

- AIR pump

-AIR relay and related control circuit

- AIR pipe or hose restriction or leak.

- DTC P0412 -- An AIR valve relay coil circuit fault has been detected. This diagnostic runs continuously.

- DTC P0418 -- An AIR pump relay coil circuit fault has been detected. This diagnostic runs continuously.

- DTC P2430 -- An AIR pressure sensor signal change fault has been detected during Phase 1 and /or Phase 2.

- DTC P2431 -- An AIR pressure sensor value versus the BARO sensor value fault has been detected. This diagnostic runs continuously.

- DTC P2432 -- The AIR pressure sensor signal voltage is below the minimum range of the sensor. This diagnostic runs continuously.

- DTC P2433 -- The AIR pressure sensor signal voltage is above the maximum range of the sensor. This diagnostic runs continuously.

- DTC P2440--An AIR system airflow leak has been detected during Phase 2.

- DTC P2444 -- An AIR pump stuck ON fault condition has been detected during 
Phase 3.

SAI System Verification

The following procedure determines if the SAI system is operating as designed:

1. Start and idle the engine for about 2 minutes to allow the SAI diagnostic to run and complete.

2. The start-up coolant and ambient air temperatures have to be in the specified operating range.

3. Monitor the AIR pressure parameter with a Tech 2.

4. Command the AIR pump relay ON. Only the AIR pump should operate. 
The Tech 2 parameter will indicate only that the AIR pump relay is commanded ON.

5. Command the AIR solenoid valve relay ON. The AIR pump should operate and the AIR solenoid/check valve should open. The Tech 2 parameter will indicate that both AIR relays are commanded ON.

6. The AIR pressure parameter should increase. The difference in readings between step 3 and step 6 should be greater than 10kPa.

If it's less than 10kPa, review the scan tool DTC information and refer to SI for service procedures.

TIP: The SAI system diagnostic tests may call for bypassing the AIR pump relay with a 60A fused jumper wire. The AIR shut-off valve will remain closed, causing a deadheaded condition. This builds an abnormal amount of heat in the pump. DO NOT operate the AIR pump for more than 30 seconds under these conditions.

TIP: When using the Tech 2 to command the AIR pump ON, a timer in the ECM and Tech 2 will automatically stop AIR pump operation. This will avoid overheating and damaging the AIR pump motor.

TIP: AIR pump operation is affected by system voltage. If the electrical system is not operating properly, correct the condition before diagnosing the SAI system.

- Thanks to Frank Tornambe and Michael Schallmo