SAI system - fault symptoms and diagnosis

Modern petrol cars are increasingly equipped with auxiliary emission reduction systems, one of which is the secondary air system. It is designed to reduce harmful emissions during engine warm-up and is activated during the start-up phase. Despite its simple logic, the system wears out over time, which can lead to malfunctions, electronic errors and even a deterioration in the car's performance.

How the SAI system works

The secondary air injection (SAI) system is responsible for reducing harmful emissions during cold engine start-up and reducing emissions after a cold start. At this point, the catalytic converter has not yet reached its operating temperature and is unable to effectively neutralise exhaust gases.

To speed up the warm-up process, the secondary air pump supplies additional air to the exhaust manifold. The oxygen in this air promotes more active oxidation of residual hydrocarbons (HC) and carbon monoxide (CO), which reduces emissions during the first few minutes of engine operation.

Main components of the system:

• Secondary air pump – creates the necessary pressure
• Check valve – prevents exhaust gases from returning to the system
• Pipes – air circulates through them
• Additional air valve – opens under vacuum pressure
• Electronic control unit – coordinates the operation of the system

The SAI is controlled by the engine control unit, taking into account signals from the lambda sensors and temperature sensors.

In which cars is the SAI system most commonly installed?

The SAI system is not uncommon in petrol cars that comply with modern environmental standards (Euro 4, 5, 6). The system is most commonly found in the following cars:

• Audi, Volkswagen, Skoda, Seat — models with 1.4 TSI, 1.8 TSI, 2.0 TFSI petrol engines
• BMW — E60, E90, F10 series with N52, N53 and N54 engines
• Mercedes-Benz — petrol models with M272/M273 engines
• Toyota/Lexus — models with 2GR-FE and 1AZ-FE engines, including hybrids
• Opel — Z16XER and Z18XER engines (Astra H, Zafira B)
• Peugeot/Citroën — models with 1.6 THP engines
• Porsche Cayenne, VW Touareg — V6 petrol versions

Most often, the system fails due to age, mileage or operation in a city cycle with frequent cold starts. In some cases, disabling the SAI is a more cost-effective solution than complex repairs.

Symptoms of SAI malfunction

Malfunctions in the auxiliary air supply system can manifest themselves in different ways — from noise during start-up to the appearance of an error code in the control unit. Before deciding on repair or disconnection, it is worth paying attention to the typical signs of problems.

The most common symptoms:

• Difficult cold start
• Increased fuel consumption
• Noise from the secondary air pump
• Diagnostic errors related to catalyst efficiency
• Exhaust fumes in the passenger compartment
• Failure to pass emissions test
• Insufficient vacuum in the intake manifold
• Unstable operation of lambda sensors after start-up

These symptoms do not necessarily indicate a problem with the SAI, but in any case, they are a serious reason to contact a car repair shop.

How to diagnose SAI malfunctions

Diagnosing the system requires the use of an OBD2 scanner as well as a physical inspection of the components. It is important to comprehensively assess the condition of both the electronic and mechanical parts of the system. Here is how the key elements are usually checked:

Correct diagnostics not only allows you to identify the malfunction, but also to assess the economic feasibility of further repairs.

When and why should you disable SAI?

In some cases, programmatically disabling the SAI secondary air supply system is a more justified solution than repairing it. This is especially true for cars with high mileage, where replacing the secondary air pump, valves and pipes can be significantly more expensive than deactivation itself.

At the STS service centre, customers are offered a competent solution to the problem without damaging other car systems. The procedure is carried out legally, using software and, if necessary, mechanical dismantling of individual components.

The most common reasons for deactivation:

1. Failure of the secondary air pump, which cannot be repaired
2. Jamming of the check valve or additional air valve
3. Cracks in the pipes, causing pressure to drop
4. Unstable operation of the control unit or incorrect firmware
5. Frequent errors that make it impossible to run diagnostics

Deactivation methods: what are the options?

Depending on the car model and the customer's budget, STS can offer several deactivation options. Below is a comparison table of the methods most commonly used in practice.

Each of these options is implemented taking into account the specifics of the car model and the owner's wishes.

How much does SAI deactivation cost?

The final cost of the procedure can be determined by specialists after a diagnostic inspection. However, on average, at STS, it is between PLN 500 and PLN 1,500. The price depends on the complexity of access to the system components, the type of engine, and the selected method of deactivation. All work is performed by certified specialists using modern equipment, so the driver receives a full warranty for the service.