Purpose of the Device Control
The air pump device control is a service diagnostic aid, which is used to determine if the air pump system is functioning properly. The air pump system may consist of wires, relays, control solenoids, hoses and pipes, control and check valves, and the air pump itself that is used to inject air into the exhaust stream.
Methodology
The device control allows the enabling and disabling of the air pump and monitoring for a change in the exhaust stream due to the presence of additional air when the air pump is turned on. Typically the short term fuel trim (integrator) data parameter is monitored throughout the device control. The presence of extra air injected in the exhaust stream will typically cause the closed loop fuel control to react to the lean state by adding fuel through increasing the short-term fuel trim. Monitoring the short-term fuel trim while exercising the air pump will provide an indication of whether the air is actually flowing into the exhaust stream when commanded. During this test, the long-term fuel trim learning (BLM learning) should be disabled by the scan tool, so that all the compensation is handled through the integrator and so that this test does not corrupt the BLM’s. On some applications, separate long term fuel trim cells exist when the A.I.R. pump is in use. For these applications, the long term fuel trim (BLM) may need to be monitored along with the short term fuel trim (integrator) since the compensation may mostly be handled by the long term fuel trim.
Preconditions
A.I.R. Pump Off
The PCM software accepts a request message from the scan tool to turn off the A.I.R. pump if and only if the following device control limit is met:
1. The vehicle being tested is equipped with an A.I.R. pump.
A.I.R. Pump On
The PCM software accepts a request message from the scan tool to turn on the A.I.R. pump if and only if all of the following device control limits are met:
1. The vehicle being tested is equipped with an A.I.R. pump.
2. The device control generic timer time-out is not active. The generic timer time-out becomes active for 60 seconds following a device control command that enables the A.I.R. pump continuously for 30 seconds.
