An active secondary air injection system uses an electric or belt-driven pump to move air for injection into the exhaust stream. Most of the time, the system consists of a pump and a check valve. Sometimes it consists of electrical controls such as relays and sensors and connecting hoses and pipes.
Usually, there is a self-diagnostic process that will turn on an engine warning light if problems are detected. Common problems are the failure of the pump motor due to moisture build-up (usually it operates in a sealed environment subject to condensation build-up) and check valve failure due to build-up of deposits from the exhaust stream.
Costs of Repair for an Active System
- For a 2006 Chevrolet Cobalt with a 2.2-liter engine, the labour time (assuming labour charges to be £70 for workshops and £100 for factory dealership jobs) to replace the secondary air injection pump (also called a “smog pump”) is estimated at 1 hour. A factory replacement part costs about £200, and a non-factory part costs about £150. This makes the secondary air injection system repair cost about £270 using OE parts in total, or about £220 using aftermarket parts. The Cobalt system also uses a check valve. The labour time to replace the check valve is estimated at 1.2 hours. A factory replacement valve costs about £270, and a non-OEM part costs about £90. The total cost to complete the job would be about £350 using factory components or around £175 using aftermarket parts.
- For a 1999 Ford Taurus with a 3-liter engine, the labour time to replace the secondary air pump is estimated at 0.6 of an hour. A factory replacement pump costs around £170, and a non-factory part costs about £95. The job would cost around £210 to complete using factory components, or about £140 using aftermarket parts.
- For a 2001 Volkswagen Golf with a 2.0-liter engine, the labour time to replace the secondary air pump is around 0.6 of an hour. A factory part costs about £660, and a non-OEM component costs about £220. This job would cost around £700 using factory parts, or about £260 using aftermarket parts. The system also uses a check valve. The labour time to replace it would be around 0.4 of an hour, and a factory part costs about £115. The total cost for the job would be about £150.
Secondary Air Injection Repair
The secondary air injection system is relatively simple in principle. About 80% of vehicle emissions occur during the engine warm-up process. The car’s catalytic converters don’t process exhaust emissions well until they reach a critical operating temperature. The secondary air injection system works to rapidly increase the catalytic converter’s temperatures on a cold start, reducing emissions.
On older cars, the process was to inject air into the exhaust stream before the catalytic converter. Exhaust gases, tend to be high in unburned hydrocarbons and low in oxygen, especially when the engine is cold. By injecting air into the system, the hydrocarbons can react with oxygen. This creates low-level secondary combustion, consuming hydrocarbons and generating heat.
This brings the catalytic converter up to its critical operating temperature relatively quickly. During this time, it takes over the role of converting hydrocarbons to reduce emissions, and the secondary air injection system shuts down.
There are two kinds of secondary air systems. In a passive system, there is a complex reed valve assembly that harvests vacuum pulses from the exhaust system and uses them to move air.
This is an older design that only works when the engine is idling. In an active system, there is a pump that moves air, and the function of the two is the same. However, the parts involved and the diagnostic procedures are largely different, so they’ll be considered separately.
Today, most newer vehicles don’t use a secondary air injection system. Rapid catalytic converter warms up and the minimization of unburned hydrocarbons on cold start is achieved by a variety of means. These include variable valve timing and ignition timing controls; heating elements in the O2 sensors; and more advanced compositions and designs of the catalytic converter.
Repairing a Passive Secondary Air Injection System
The general design of a passive secondary air injection system usually consists of an air control and bypass valve, piping between the intake and exhaust systems, and one or two check valves. One of the difficulties of repairing the system is the general lack of availability of parts.
During the era when this kind of system was common, there was little in the way of on-board self-diagnostics. While a failed secondary air injection system has some effect on the vehicle’s emissions, it doesn’t usually impact how the vehicle runs. Additionally, emissions inspections were also less common. This means that the system could well have been working very poorly and would never have been noticed, and therefore these parts were rarely serviced.
Also, the lack of contemporary demand led to a lack of aftermarket parts. Then again, most auto manufacturers have a policy of discontinuing parts from factory stocks after 15 or so years, so factory parts are also generally unavailable.
This leads to the unusual problem that if a passive secondary air system fails, there are usually no new parts available to repair it. Sometimes, used parts can be sourced, and sometimes new-old-stock (NOS) parts can be found with some effort.
One problem with the system is the buildup of deposits in the air pipes, much like how an EGR system (which also deals with exhaust gases) can develop problems. Pipes can be removed, inspected, and cleaned if necessary.
Sometimes, the metal parts of the air control and bypass valves can also be removed and cleaned, which can sometimes resolve problems. In these cases, there isn’t any book time or predictable repair procedures and, by extension, no practical way to make a reliable estimate.
It can be safely mentioned here that, based on the typical location and accessibility of the system in any given engine, a passive air intake system could be fully removed from most vehicles in about two hours. The time for assessment of parts, cleaning of parts, and sourcing of replacement parts, if necessary, is harder to estimate.