2004 Secondary AIR Injection (AIR) System

The Secondary AIR system used in the 2004 TrailBlazer, Envoy, Rainier and Bravada with the 4.2L in-line 6-cylinder engine incorporates a new AIR pump and an electronic AIR shut-off valve.

AIR System Operation
AIR is an emission control system that forces fresh air into the exhaust system to accelerate catalyst operation. This reduces HC and CO emission levels.

The AIR pump normally operates for approximately 20 seconds on start-up when the coolant temperature is between 37° and 122° F (3° and 50° C) and the ambient air temperature is between 32° and 304° F (1° and 151° C).

Notice that the AIR pump is inhibited when the ambient temperature is below freezing, to prevent damage if moisture is present in the pump. And when the engine is at operating temperature, the AIR pump is inhibited, because the catalyst is warm enough to start operating efficiently.

Features of the New AIR Pump
The AIR system consists of the AIR pump (fig. 1), AIR pump relay, AIR solenoid relay, electronic shut-off valve, pipes and related wiring.

The AIR pump and AIR pump relay are located on the underbody of the truck, beneath the driver’s seat (fig. 2).

A AIR Pump Relay
B Inlet Pipe
C Front
D AIR Pump
E Outlet Pipe

The new AIR pump is a centrifugal-impeller type and is hermetically sealed. The case is sonically welded and pressure tested against water leaks. The bearings are permanently lubricated and sealed, and require no maintenance.
The AIR pump’s inlet and outlet pipe- fittings are different diameters to prevent incorrect pipe connections (fig. 3).

Current Draw
An interesting property of a centrifugal-impeller pump is that if there is a restriction, or no air is flowing, the pump has to perform less work. The motor runs faster and current draw is lower. Earlier AIR pumps were a regenerative turbine-impeller type that works harder as the restriction increases. An internal circuit breaker can help prolong the life of the AIR pump in a constant run situation, like a stuck-closed AIR pump relay.

TIP: If a problem exists in any of the AIR pump motor circuits, the circuit breaker may allow the pump to operate intermittently to prevent motor damage.

Possible causes include:
- a short to voltage in the supply voltage circuit of the AIR pump
- a shorted (sticking closed) AIR pump relay
- a short to ground in the control circuit of the AIR pump relay.

DO NOT conclude the AIR pump is at fault if pump operation is intermittent.

The in-rush current of the AIR pump is approximately 140 amps. During continuous operation, the current draw is 35 to 40 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.

TIP: The resistance mentioned above also applies to the AIR pump relay switched side voltage circuits.

Voltage drop tests have been integrated into the AIR service diagnostics to pinpoint these improper resistance conditions.

Electronic Shut-Off Valve
The electronic shut-off valve contains an integral solenoid and check valve (fig. 4). The valve has no removable parts and the solenoid and valve are serviced as an assembly. The current draw of the solenoid is 2.5 to 5 amps. This high current draw requires the addition of a relay to protect the control module driver. A resistance greater than 15 to 17 ohms in either the voltage supply or ground circuits of the solenoid will affect valve operation.

The shut-off valve opens reliably when commanded ON by the control module. Because the valve is electronically operated instead of by vacuum, conditions such as low manifold vacuum, high altitude or heavy acceleration have no adverse effects on the operation of the valve. The internal check valve protects caustic exhaust gases from damaging the AIR system components.

Diagnosis
There is only one DTC, P0410. It results from no airflow in the system. The diagnostic relies on the heated oxygen sensor (HO2S) 1 voltage parameter to drop below 150mV. The AIR diagnostic will run only on ignition cycles when the pump is commanded ON by the PCM. If this test passes, then no active test will run. If the passive test fails, or is inconclusive, the active test will run later in that ignition cycle. At that time there will be a maximum of two 3-second active tests.

The AIR pump can be commanded ON and OFF using the Output Controls menu of the Tech 2. Observe the HO2S 1 voltage parameter when the engine is running, and the fuel control is in closed loop.

When the AIR pump is commanded ON, the HO2S 1 voltage parameter will decrease below 150 mV to show a properly operating AIR system. A timer in the PCM disables AIR pump operation after approximately 30 seconds to protect the vehicle’s components.

TIP: The commanded state of the AIR pump relay may also be observed in the fuel trim data list.

When performing AIR system diagnostic tests, or using output controls on the Tech 2, DO NOT operate the AIR pump for more than 30 seconds, to avoid overheating the motor. Under some conditions, such as bypassing the AIR pump relay with a fused jumper wire, the AIR shut-off valve will remain closed, causing a deadheaded condition. This builds up an abnormal amount of heat in the pump.

Refer to SI for service procedures.

- Thanks to Frank Tornambe

figure 2

A new feature is being phased into the Tech 2, beginning with TIS satellite version 9.0, Tech 2 software version 23.005, released late in August. Software version 23.005 must be installed for this feature to work.

This information applies to most 2004 vehicles. And initially, it will operate on most body systems (such as radio, door modules, OnStar, BCM, HVAC, liftgate module, IPC module), chassis and powertrain.

The new feature has to do with Request Information, which is a necessary step in programming a module.

In the past, you had to go to the Diagnostics menu to perform diagnostic functions. Then, if diagnosis indicated that it was necessary to install a new module, you had to exit Diagnostics and go back to the Service Programming System menu to Request Information. This had two drawbacks. First, you had to “build’ the vehicle again. And when the Request Information function was performed, the Tech 2 downloaded information from every module on the vehicle, not just the one you were working on. Both of these steps took time.

TIP: Get in the habit of trying this feature, even though it’s not available on all vehicles yet. If it doesn’t appear when diagnosing a specific vehicle, the tool isn’t faulty -- it just isn’t supported yet.

With the new feature, when you’re in Diagnostics, you will be able to go directly to Request Information in the Special Function menu. This has three immediate timesaving advantages. First, you don’t have to leave Diagnostics. Second, this means that you won’t have to “re-build” the vehicle. And third, only the module you’re working on is commanded to download information. All the other modules on the vehicle remain uninvolved.

TIP: Once Request Information is performed on the new module you’ve just installed, you will then have to connect your Tech 2 to TIS to download the latest calibrations.

TIP: When you reconnect the Tech 2 to the vehicle to program the module, you must use the Service Progarmming System menu.

- Thanks to Mark Stesney

A rattle or buzz from the right front speaker on a 2000-04 Sunfire or Cavalier may be generated by the door trim panel upper extension covering the exterior mirror mount (commonly known as the shark fin) (fig. 5). Before replacing the speaker, verify that the shark fin is not the concern. Apply pressure to the shark fin at the forward lower corner. If the rattle diminishes, repair the concern by removing the trim panel (refer to SI Document 1043347). Add a foam block to the forward lower corner to dampen the low frequency vibrations. Install the trim panel and tighten the screw to 1.3 Nm or 12 lb in.

- Thanks to Mark Alward

figure 5

Refer to bulletin 03-06-03-001. These are the highlights.

Owners of 2003 C/K trucks with the 5.3L Engine (VIN Z -- RPO L59), and 2004 C/K trucks with any engine, may comment that the engine starter continues to run after the key is released (ghost crank).

This is a normal condition and no repairs should be attempted for this condition.

On these vehicles, the starter relay is controlled by the PCM, with input from the key switch. After 0.4 seconds of cranking, a timer is activated in the PCM. Once this happens, even though the key is released, the PCM will continue to crank the starter until the engine starts or a no-start time limit is reached.

The fuel pump module may take several seconds to build fuel pressure, particularly after sitting overnight. The automatic crank feature ensures sufficient crank time even if the customer releases the ignition switch prematurely.

- Thanks to Jim Mauney and Jay Dankovich

A number of modules included on cars and trucks need to be configured to the vehicle when a replacement is installed. A table has been prepared to cover all cars and light duty trucks for the 2004 Model Year. Go to the Reference Guide tab.

The table indicates the type of action required; you must refer to SI 2000 for procedures and details.

The modules listed across the top of the table require configuring to the vehicle after installation. All of the vehicles are listed in the left column. Here’s how to interpret the symbols in the table.

- S indicates need for SPS (service programming).
- O indicates set-up required with or without Tech 2
- A indicates actuator set-up is required.
- T indicates an on-vehicle tire pressure monitor programming procedure is required using special tool J-41760

These symbol interpretations also appear in the bottom-left corner of the table.

The following modules may be installed on certain vehicles, but require no action, so they are not included in the table:
- Heated Seat Module
- Head Up Display
- Rear Park Assist
- Driver Information Center
- CD Changer
- Fuel Injector Control Modules (for alternative fuel vehicles only)

- Thanks to Lindsey Beauchamp

Ashtray Repair Spring

If a spring breaks on the ashtray of a 2000-04 Buick LeSabre, it’s not necessary to replace the entire ashtray.

There are two springs, right and left (fig. 6). In some cases, the ashtray was built with two same-side springs. If this happens, a spring may deform, causing the ashtray to hang up.

Repair springs are now available from SPO. The right-hand wound spring is 89042051 and the left-hand wound spring is 89042084.

- Thanks to Bill Metoyer and Martin Tulashie

Beginning in the 2004 model year, OnStar will introduce the latest generation of hardware, Gen 6. This is the first OnStar hardware that supports CDMA and PCS digital cellular communication, along with AMPS, analog cellular.

Rollout Schedule
The Pontiac Aztek and Buick Rendezvous will receive Gen 6 by the fourth quarter of 2003. All full-sized trucks are scheduled by the first quarter of 2004. The remainder of the fleet will adopt Gen 6 throughout the 2004 and 2005 model years. Exact timing has not been finalized.

FCC Ruling Affecting U.S. Market
Recently, the Federal Communications Commission (FCC) ruled that, in the U.S., wireless carriers will no longer be required to support the analog wireless network after February 16, 2008. After that time, if U.S. carriers for OnStar elect to provide only digital service, OnStar service will be available only through dual-mode (analog/digital) hardware.

From the beginning, OnStar has relied on a nationwide analog wireless network to provide communication to and from OnStar-equipped vehicles. Today, the analog network continues to provide the most extensive coverage across the U.S. and Canada.

As of June 2003, all OnStar systems utilize analog-only hardware. However, the U.S. wireless carriers have begun to shift from analog to digital networks, and so will OnStar.

The Gen 6 OnStar system brings some new features, including:
- An enhanced voice recognition system, including continuous digit dialing, which can accept a phone number in a continous string as opposed to one digit at a time
- Quicker response to door unlocks

In digital markets, the module has a DRx standby mode. The module will stay awake 1 hour in a lower power mode following key off.

What You Need to Know About OnStar Hardware in GM Vehicles
TIP: When attempting to diagnose a vehicle with the Gen 6 OnStar module, refer to Service Information for the latest diagnostic information.

The OnStar-equipped vehicle has one of three types of hardware.

Analog-only: Most 2003 model year and earlier vehicles have analog-only hardware. The FCC ruling requires that U.S. wireless carriers provide reliable, nationwide analog service until February 2008. We do not anticipate that OnStar service will be affected in any way during the five-year transition period. However, if the carriers for OnStar elect to provide only digital service after that, then beginning Feb. 16, 2008, OnStar service will be available only through dual-mode (analog/digital) hardware.

Analog/Digital-Ready: Some 2003 and 2004 model year vehicles have analog/digital-ready hardware. These vehicles have been prepared for conversion to analog/digital (dual mode) hardware when it becomes available.

Analog/Digital (Dual-Mode): Some 2004 and future OnStar-equipped vehicles feature dual-mode (analog/digital) hardware, which will be unaffected by the FCC ruling.

OnStar will notify customers directly if they will be affected by this ruling, along with plans to accommodate customers who wish to continue as OnStar subscribers.

As OnStar hardware continues to change, keeping track of which vehicle has which OnStar hardware generation becomes more complicated. To determine which hardware generation is in a vehicle, you can use any of these tools:
- OnStar Window Label (current production vehicles forward)
- OnStar Hardware Generation Identification Quick Reference Guide (see Reference Guides tab at the top of this page)
- The accompanying what-to-do table (which assumes the OnStar system is operational)

- Thanks to Dale Tripp

OnStar Introduces Factory Activation

Note these corrections to bulletin 01-08-46-008.

1. The GMC Jimmy is not listed for an upgrade and is capable.

2. Pontiac Bonneville was inadvertently left off the listings. Bulletin incorrect to upgrade this vehicle. Listing should read as below.

3. The Escalade and Denali cannot be upgraded; as it is a distinct body style, different from the Yukon and Yukon XL.

All vehicles involved with this upgrade must have the factory installed option OnStar system and not the dealer installed unit.

- Thanks to Jim Mikolaizik

Repairing Napped Fabric

HSeats on the following vehicles may be upholstered in napped fabrics, with Dorchester on the bolster and Honeycomb on the insert.

1999-04 Silverado
2000-04 Tahoe and Suburban
2002-04 Avalanche
1997-2003 Grand Prix

Under some circumstances, the nap may become crushed down, giving the appearance of being worn out.

TIP: If the base material is visible (fig. 8), the material is worn, and this procedure is not a remedy.

If the base material is not visible, use a small wire brush (fig. 9) to carefully raise the nap (fig. 10 and 11). Wire brushes similar to the one shown are available at most hardware and home stores.

It is not necessary to use water or cleaners to perform this procedure.

A Before
B After

- Thanks to Jerry Garfield

figure 8

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On the 2004 Cadillac SRX, due to dissimilar front and rear tire widths, the tire and wheel assemblies cannot be rotated from front to back. They may be rotated from side to side. Wheel and tires sizes are based on the engine in the vehicle.

- Thanks to Sean Garrison

Truck Issues – Fix It Right The First Time

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