Fault code P0492 is called “Secondary Air Injection System Insufficient Flow (Bank 2)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0492
Error code P0492 refers to the emission system. The AIR pump directs air into the exhaust to reduce emissions. It takes in outside air and pumps it through two one-way check valves into each exhaust outlet group.
A stored code indicates that the Powertrain Control Module (PCM) has detected a decrease in secondary air intake (SAI) capacity. Bank #2 indicates the side of the engine where cylinder number one is not located.
The purpose of the system is to force atmospheric air into the exhaust system during cold starts.
This helps to burn unburned or partially burned hydrocarbon molecules in the exhaust gas stream. Which results from incomplete combustion during cold starts when the engine is running on a highly enriched fuel-air mixture.
Secondary air systems usually consist of a high-power air pump in the form of a turbine, a relay to control the pump motor on and off. As well as a solenoid and a check valve to control the air flow. In addition, there are various tubes and ducts corresponding to the application.
In vehicles equipped with electric pumps, the PCM controls the SAI pressure sensors and turns the pump on when necessary. The system relay is used to transfer battery voltage through the fuse panel or fusible link to the SAI pump.
If the PCM detects insufficient secondary air injection system flow, which indicates that a fault has occurred. Then code P0492 will be stored and the malfunction indicator light may illuminate.
Symptoms of vehicle malfunctions
The main signal that an error P0492 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
- On some European vehicles, the contamination control light will illuminate.
- Mechanical noises caused by a damaged air pump.
- Engine stalls or starts poorly.
- Jerking/missing ignition at idle during warm-up cycle.
- Poor acceleration while engine is cold.
- Sometimes there may be no symptoms, despite the stored fault code.
Error code P0492 very rarely causes drivability problems or other symptoms after the catalytic converter has reached operating temperature. But the car is unlikely to pass the emissions test with a cold engine because the emissions will increase.
Factors that can cause this error code
The error code P0492 can mean that one or more of the following problems have occurred:
- Exhaust manifold check valve is defective.
- Defective SAI air pump.
- Secondary air injection pump relay is defective.
- Moisture in pump and motor.
- Broken or interrupted power supply to SAI system due to bad connections or damaged wiring.
- Blown SAI system fuse.
- Leaking vacuum hose.
- Secondary air injection port may be clogged.
- Clogged air passages preventing the injected air from entering.
How to fix or reset OBD-2 code P0492
Some suggested steps for troubleshooting and fix the error code P0492:
- Connect the OBD-II scanner to the vehicle’s diagnostic connector and read all stored data and error codes.
- Eliminate any other errors that may be present before proceeding to diagnose code P0492.
- Visually inspect the electrical wires and connectors related to the SAI system.
- If necessary, repair or replace any shorted, broken, damaged, or corroded components.
- Check the SAI secondary air pump relay.
- Test the secondary air pump resistance.
- Inspect vacuum lines for leaks or blockage.
Diagnose and repair of problems
Code P0492 is set when there is no outside air to burn off excess hydrocarbons in the exhaust system during a cold start. This causes the voltage on the front oxygen sensor not to drop to the set level.
The diagnostic procedure requires the engine to be cold, ideally with the vehicle idling for at least 10-12 hours. After that, it is necessary to connect the diagnostic device and start the engine.
Checking the electrics
The voltage at the front oxygen sensor should drop below 0.125 volts after about 5-10 seconds. A fault in the secondary air system will be confirmed if the voltage does not drop to this value.
If the voltage does not drop to 0.125 volts, but you can hear the air pump running, check all hoses, air lines, valves and solenoids for leaks. Also remember to check all hoses, ducts and valves for obstructions such as carbon buildup or other blockages.
If the air pump won’t turn on, check all relevant fuses, relays, wiring, and pump motor for continuity. If necessary, replace or repair failed components.
When all checks have been completed but the P0492 malfunction persists, it may be necessary to remove the exhaust manifold or cylinder head. To gain access to the air passages for the purpose of cleaning the fouling.
Vacuum check
Remove the hose from the check valve, check to see if air is escaping from it when the engine is started. Keep the engine running, after a minute the valve should close and stop the air supply, if it does then the check valve is good.
If the valve stays open, the valve is probably defective. If the valve is permanently closed, the problem is probably in the vacuum control switch.
Inspect the vacuum lines from the check valve to the switch. Look for hard spots, cracks, or loose connections. Replace hoses if you find faulty areas.
Test the control switch vacuum inlet line. Connect a vacuum gauge to the inlet hose to check the manifold vacuum, with the engine running. If there is no vacuum, replace the vacuum line and retest for error P0492.
Apply vacuum to the inlet nipple of the vacuum control relay. The valve should be closed and the pump should not hold pressure. Apply 12 V to the two control switch terminals with jumpers. If the switch does not open and does not relieve the vacuum from the pump, the switch must be replaced.
On which vehicles does this problem occur most frequently
Fault code P0492 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Audi (A6, A8)
- BMW (325i, 525i, 745li, E90, X5)
- Porsche (Cayenne)
- Toyota (Tundra)
- Volkswagen (Passat, Touareg)
Fault code P0492 can sometimes be found with other errors. The most common are the following: P0102, P0313, P0335, P0340, P0410, P0411, P0412, P0413, P0414, P0415, P0416, P0417, P0418, P0419, P041F, P044F, P0491, P0727, P1082, P1602, P2096.
