Is your GM Truck with the 4.8L, 5.3L or 6.0L engine experiencing a rough idle? Or is your check engine light on, with codes PO300, PO171, PO174 and PO332?

These two conditions seem to be very common, and requires similar repair procedures (removal of the intake manifold). Gm has recognized these problems and has issued a parts revision and TSB (Technical Service Bulletin) to repair these symptoms.

First we will talk about a rough idle. Most vehicle owners complain about a rough idle or a misfire when the engine is cold, and as the engine warms up the problem goes away??? But, leaving your check engine light on, with codes PO300, PO171 and PO174. PO300 is a misfire code that is usually fixed by new ignition parts like spark plugs and wires. But, when accompanied by PO171 and PO174, this indicates a Fuel Trim problem. The engine may be running to lean, due to a intake vacuum leak. When your vehicles engine is cold, the PCM (power control module) is running in ‘closed loop’ a predetermined run program. As the engine reaches normal operating temperature the PCM switches to ‘open loop’ using the engine control sensors to read the data from the engine to refine the running condition. One of these sensors is a oxygen sensor, this monitors the air/fuel ratios in the exhaust to calculate the amount of fuel to deliver to the engine. With a vacuum leak the the computer controls can not calculate for the extra air in the engine, making a lean condition. The oxygen sensor sees the lean condition and the PCM increases the amount of fuel to the engine to compensate. This is called fuel trim, as the fuel trim enrichment reaches 25% or more adjustment the PCM sets a code for the problem.

GM has recognized two part problems with sealing of the plastic intake manifold, the intake gaskets and bolts. The original red/orange gasket has be revised to a teal green colored gasket were the material has been updated. The bolts are sleeved with a rubber crush washer and require a special torque sequence to insure a proper seal. The intake bolts should NEVER be reused!

GM has also issued a TSB (02-06-04-023A) for code PO332 (knock sensor), which may be heard as a mild to severe engine ping usually sounding worse on acceleration. This condition is a result of corrosion on the rear bank knock sensor due to water intrusion into the sensor cavity. This condition is more frequent on vehicles that the owner washes the engine compartment.

To correct the Knock sensor problem requires replacement of the rear knock sensor (their is also a front knock sensor,  we also recommend replacing) and building a dam (wall) around the sensor using RTV to divert water away from the sensor.

APDTY’s kit comes with Intake Gaskets, Foam Pads, Intake Bolts, RTV and Knock Sensor(s) and Optional  Wiring Harness

Tighten the intake manifold bolts in sequence, tighten on first pass to 44Lb in. On the final pass torque to 89Lb in.

What is a Electronic Throttle Body or commonly referred to as Throttle-By-Wire, Fly-By-Wire, Drive-By-Wire (DBW) or Throttle Actuator Control (TAC)?

Electronic Throttle Bodies? Where’s the throttle cable? As you may already know opening the hood in a modern car reveals systems alot different than that of years past. As engine life has been extended and engine controls have become more complex, longer-life and higher-reliability electronic components are required. These advances in electronic componets aid the Power Control Module (PCM) to stay within the programed perimeters for the best performance and emission regulations.  One of these components being the Electronic Throttle Control (ETC) system often referred to as throttle-by-wire, fly-by-wire, drive-by-wire (DBW) or throttle actuator control (TAC). Using a array of sensors the on-board computer system measures throttle demand, then sends out a signal (electronic command) to the electronic throttle body. This computer command is to operate a servo motor controlling the throttle plate/blade or butterfly.

What seems to be the failure of the Electronic Throttle Body is the plastic gear drive. A common problem of the throttle body bore has been a build up of gases from the EGR and PVC systems, combined with heat causes a formation of gummy residue. This gummy residue often restricts airflow causing poor or hunting idle and even stalling conditions. This residue can become so built up that it causes the throttle body plate/blade to stick, striping out the gear drive in the throttle body.

TechSmart™ has a complete line of New Electronic Throttle Bodies, offering a cost effective solution for repairing  failed electronic throttle bodies for many makes and models.

2010-2009 Ford Light Truck Expedition
2010-2009 Ford Light Truck F Series Fullsize Pickup
2010-2009 Lincoln Navigator

2007-2006 Cadillac CTS
2008-2006 Chevrolet Corvette
2009-2008 Pontiac G8
2006-2005 Pontiac GTO

2007-2006 Buick Rendezvous
2006-2005 Buick Terraza
2006-2005 Chevrolet Malibu / Malibu Maxx
2006-2005 Chevrolet Light Truck Equinox
2006-2005 Chevrolet Light Truck Uplander
2006-2005 Pontiac G6
2006-2005 Pontiac Montana
2006-2005 Saturn Relay

2008-2006 Buick LaCrosse
2006 Buick Rendezvous
2007-2006 Cadillac CTS
2006 Cadillac SRX
2007-2006 Cadillac STS

2006-2004 Cadillac SRX
2009-2006 Cadillac XLR
2006-2005 Pontiac Torrent

2004 Buick Rainier,
2006-2003 Cadillac Escalade,
2006-2003 Chevrolet Light Truck Fullsize Pickup
2007-2004 Chevrolet Light Truck G Series Fullsize Van / Express
2006-2003 Chevrolet Light Truck Suburban / Fullsize Blazer / Tahoe
2004-2003 Chevrolet Light Truck Trailblazer
2004-2003 GMC Light Truck Envoy,
2006-2003 GMC Light Truck Fullsize Pickup
2007-2004 GMC Light Truck G Series Fullsize Van / Savana
2006-2003 GMC Light Truck Suburban / Fullsize Jimmy / Yukon
2007-2005 Hummer H2

2004-2003 Oldsmobile Bravada
2007 Chevrolet Light Truck Colorado
2007 GMC Light Truck Canyon
2007 Hummer H3
2007-2003 Buick Rainier
2007-2003 Chevrolet Light Truck Trailblazer
2007-2003 GMC Light Truck Envoy
07-05 Pontiac Grand Prix
2007-2005 Saab 9-7
2007-2006 Chevrolet Impala

2007 Saturn Aura
2009 Saturn Vue
2009,2010 Buick Lucerne
2009,2010 Chevrolet Impala
2009-2006 Chevrolet Light Truck Uplander
2009-2006 Pontiac Montana
2009-2006,2010 Chevrolet Malibu / Malibu Maxx
2009-2006,2010 Pontiac G6
2009-2007 Chevrolet Light Truck Equinox
2009-2007 Pontiac Torrent

2001-1999 Cadillac Catera
2004-2003 Cadillac CTS

2002 Chevrolet Light Truck Trailblazer
2002 GMC Light Truck Envoy
2002 Oldsmobile Bravada

2008-2005 Pontiac Grand Prix
2008-2006 Buick Lucerne
2009-2005 Buick LaCrosse

2007 Chevrolet Light Truck Colorado
2007 GMC Light Truck Canyon
2007-2004 Saturn Ion
2007-2005 Chevrolet Cobalt

2006-2003 Chevrolet Light Truck Suburban / Fullsize Blazer / Tahoe
2006-2003 GMC Light Truck Suburban / Fullsize Jimmy / Yukon
2007-2003 Chevrolet Light Truck Fullsize Pickup
2007-2003 GMC Light Truck Fullsize Pickup

2009-2008,2010 Chevrolet Light Truck HHR
2009-2008,2010 Chevrolet Malibu / Malibu Maxx
2010 Chevrolet Light Truck Equinox
2010 GMC Light Truck Terrain

2008-2007 Chevrolet Malibu / Malibu Maxx
2009-2007 Pontiac G5
2009-2007,2010 Chevrolet Cobalt
2009-2007,2010 Chevrolet Light Truck HHR

2009-2007 Saturn Outlook
2009-2007 Saturn Vue
2009-2007 Suzuki XL-7
2009-2007,2010 GMC Light Truck Acadia
2009-2008 Chevrolet Light Truck Equinox
2009-2008 Pontiac Torrent
2009-2008,2010 Buick Enclave
2010 Buick LaCrosse

2009-2007,2010 Cadillac SRX
2009-2008,2010 Cadillac CTS
2009-2008,2010 Cadillac STS
2010 Buick LaCrosse
2010 Chevrolet Camaro
2010 Chevrolet Light Truck Equinox
2010 GMC Light Truck Terrain

2009 Chevrolet Light Truck Avalanche
2009 Chevrolet Light Truck Suburban / Fullsize Blazer / Tahoe
2009 GMC Light Truck G Series Fullsize Van / Savana
2009 GMC Light Truck Suburban / Fullsize Jimmy / Yukon
2009 Hummer H2
2009-2010 Cadillac Escalade
2009-2010 Chevrolet Corvette
2009-2010 Chevrolet Light Truck Colorado
2009-2010 Chevrolet Light Truck Fullsize Pickup
2009-2010 Chevrolet Light Truck G Series Fullsize Van / Express
2009-2010 GMC Light Truck Canyon
2009-2010 GMC Light Truck Fullsize Pickup

2009-2010 Ford Crown Victoria
2009-2010 Ford Light Truck E Series Fullsize Van
2009-2010 Ford Mustang
2009-2010 Lincoln Town Car
2009-2010 Mercury Grand Marquis

2009-2010 Ford Light Truck E Series Fullsize Van
2009-2008 Ford Mustang

2008-2006 Ford Light Truck Explorer / Sport / Sport Trac
2008-2006 Mercury Mountaineer

2005-2004 Ford Light Truck Explorer / Sport / Sport Trac
2005-2004 Mercury Mountaineer

2006-2003 Chevrolet Light Truck G Series Fullsize Van / Express
2006-2003 GMC Light Truck G Series Fullsize Van / Savana

2007-2005 Ford Five Hundred,
2007-2005 Ford Light Truck Freestyle
2007-2005 Mercury Montego

2009-2006 Ford Fusion
2009-2006 Mercury Milan

2010 Ford Light Truck Transit Connect

2006 Lincoln Zephyr
2009-2006 Ford Fusion
2009-2006 Mercury Milan

2002-2001 Chevrolet Light Truck Fullsize Pickup
2002-2001 Chevrolet Light Truck G Series Fullsize Van / Express
2002-2001 GMC Light Truck Fullsize Pickup
2002-2001 GMC Light Truck G Series Fullsize Van / Savana
1999-1998 Chevrolet Light Truck P Series Van
1999-1998 GMCLight Truck P Series Van

2004-2000 Chevrolet Corvette
2005-2004 Cadillac CTS

2002 Cadillac Escalade
2002 Chevrolet Light Truck Avalanche
2002-2000 Chevrolet Light Truck Fullsize Pickup
2002-2000 GMC Light Truck Fullsize Pickup

2008-2005 Pontiac Vibe

2004 Pontiac Grand Prix

2002-1999 Chevrolet Camaro
2002-1999 Pontiac Firebird

2009-2005,2010 Ford Mustang

How To Diagnose/Fix/Repair/Remove/Replace Hummer Air Ride Suspension Components: Suspension Compressor, Air Bag(s)/Shock(s), Coil Spring Conversion Kit

Vehicles Affected:  2003-2009 Hummer H2 w/ Rear Air Suspension System

Tools Needed: Basic Hand Tools

Parts Needed: Air Suspension To Coil Spring Conversion Kit or Air Suspension Bags/Compressor & Components

Problem: The 2003-2009 Hummer H2 had an option from the factory to get a standard coil spring suspension or an air ride suspension. The air ride suspension is an awesome feature to have when it is brand new, however, over time the system can need repairs that can easily add up into the thousands of dollars. The vehicle owner really needs to know all of the possible costs involved with the normal & continuous degradation of an air suspension system. The air ride suspension consists of these parts:

Air Suspension Compressor/Dryer/Valve Body Assembly

Air Suspension Control Module (also called Air suspension brain or computer)

Air Suspension Air Bags/Springs (the proper term is air spring)

Air Ride Height Sensors/Air Ride Control Relays/Ride Height Switch – Not Available In The Aftermarket At The Time Of This Article, Consult Your Hummer/GM dealers for pricing (Order by your VIN)

The purpose of the air suspension components are to keep the vehicle visually level & to maintain a proper ride height when the vehicle is loaded or unloaded. This maintains the alignment and prevents premature tire wear. Note: Many Hummer owners switch the OE wheels to oversize wheels such as 24″ wheels, This can change the geometry of the vehicle alignment and can result in un-even tire wear.

Fergies Hummer H2

Fergie's Hummer H2 With 24 Inch Wheels & AIr Suspension

Here is a picture of Fergie’s Hummer H2 that she sold on eBay, Fergie we love you and please let us use your picture without any money as we are poor poor poor and eventually your air ride will need some repairs.

So here is what you want to read if you are deciding to convert it to a standard coil spring suspension or repair the air ride suspension. First of all, if you are reading this then most likely the rear end of your hummer is sagging or it is at the dealer and you just got the estimate to repair it. In either case the air ride suspension usually starts out with a leaking air spring or a burned out compressor. A leaking air spring is not a big deal, however consider this: Once your air bag starts leaking, it makes the air suspension compressor run longer and come on more often then it was designed for. This will shorten the life of the air suspension compressor and the absolute worst thing that can happen is you pay $200-$300 to replace one of the air springs, If you replace both air springs, then you are probably around $500. The shop calls and says it is done, you go to pick it up and see the rear-end is back up like it is suppose to, you are happy, you pay, and you leave. Everything is fine and dandy for a few months and then all of a sudden you come out to find the rear-end sagging again. You take it back to the shop thinking and hoping a small problem happened and they will get it fixed up for you and it might not cost you anything. Then you get the dreaded phone call that you air suspension compressor is burned out. The next sentence is the compressor is $2500.00 and the labor is, blah, blah, blah. At this point you are caught off guard and puzzled over the insane cost to fix this. You are thinking why did the shop not see this 3 or 5 or 8 months ago when they replaced my air springs. Well the simple answer is they cannot tell unless they take apart the compressor and do an internal inspection and unless you are willing to pay the labor to do this, well it just is not getting done. Also most shops are trained to repair the vehicle back to OE original design so they are doing what they are suppose to do and probably will not even offer the conversion kit unless you bring it up. This is why the vehicle owner should fully understand the entire system before deciding how to repair it.

So you have 2 options, 1. Spend lots of money and repair the air suspension, or

2. Convert the darn thing over to a very easy, very in-expensive, MADE IN THE USA, conversion kit that many people can install themselves if you so dare.

Here are instructions for both, Starting with the conversion kit that we strongly recommend:


1. Raise and support the vehicle properly and safely according to a GM repair manual or owners manual (We have to say it like that so in-case you drop the car off of the lift, we are not liable, we are just trying to help you)

2. Remove the rear wheels from the vehicle and set aside

3. Look at the center of the rear axle and you will see the air suspension compressor assembly behind it. It will look like the image below:    Note: The image below is a dual compressor assembly found on 2005-2007 H2 models, If you have a 2003-2004 H2, you may have the older single compressor, Read our repair instructions farther down this post for more info on the different compressors.

Actual Image Of A Brand New Air Suspension Dual Compressor Assembly

4. Remove the compressor assembly form the vehicle. First remove the air lines. If you have a proper scan tool, you can use it to depressurize the bags, If you do not, then use caution with the next step. Do not let the air shoot right into your face to avoid hurting yourself. These are quick disconnects and all you do is push in on the line until the fitting goes in, then pull the line itself out of the fitting while keeping the fitting pressed in. Play with it a few times and you will see how it works, these come right out and if done properly, very little force is needed. Then disconnect the control module or brain, this is a large plastic connector that simply unplugs, some models will have a small clip keeping the connector attached. Once you have the wiring and air lines disconnected, next unbolt the assembly form the vehicle and set aside. You will not be putting the compressor back into the vehicle if you are converting it. Also by unplugging the compressor control module, you are de-activating the suspension light on the dashboard.

5. Now go to the air springs and disconnect the air lines form the springs/bags using the same quick disconnect procedure above (push in on the fitting and then pull the line out)

6. It is safest to lower the vehicle down until the rear axle tube is about a foot off of the ground (The front wheels are still bolted to the vehicle, so if you lower it until the front wheels almost touch the ground and use a floor jack to jack up the rear axle tube to take the load off of the shock absorbers. Then unbolt the bottom bolt from the shock absorbers and slide the shocks away from the rear axle. The air springs/bags are held into place by simple clips and the shock absorber keeps the air spring from extending out too much as it can only extend out as far as the shock extends.

7. Time to remove the air springs/bags form the vehicle. The air bags are snapped into place at the bottom and the top is a turn & lock clip design. Look closely at the top of the air spring and you can see the clip, The air bags should be empty now since you disconnected the airlines. You can push down on the top clip and grab the bladder of the air spring and try and turn it by hand. These are not bolted in and you have to turn the air spring to unlock it form the clip. To release it, simply rotate the top and pull down. Here is a sketched image exploded view of the air spring:

Exploded View Of The Air Spring Bag On Hummer H2

8. The bottom of the air bag is snapped into place also, You can use a long flat head screw driver to pop it off of the clip. Remove the air springs and do what you want with them, they will not be re-used.

9. Time to install the nice new reliable and low cost steel coil springs. We are also proud to say these are manufactured right here in the USA, that is a rare thing and we strongly promote any US manufactured products. OK, Take the coil springs out of the box and look at them closely. They will have a label on them for left or right. Left is the driver side of the vehicle and right is the passenger side. Install the coil springs with the tighter wound coils on the bottom or in other words the end where the coils are closer together. (The manufacturer has changed the design on these springs a few times, look at the instructions included with the springs if it is confusing. One of the designs is both springs are identical and others their is a left & right. The kits we have at the time of writing this article came directly from General Motors and their is a right and a left.)

Exploded View Of Coil Spring Installed In Place Of The Air Spring Bag

10. With the shocks still unbolted, fit one side of the coil spring into place. You will see the spring sits onto a pre-made mount for the bottom that is exactly where the air spring was located, the top of the spring also fits into a spring seat. You will need to jack up the floor jack to get the spring to stay into place, At this point you can slide the shock bolt back into place to hold the coil spring in place. YES THIS IS DESIGNED THIS WAY BY GM AND IS PERFECTLY NORMAL. Their is nothing holding the spring into place except the spring seats and the shock absorber being bolted into place. DO this same process for the other spring and once you have the shock bolts into place and make sure the springs are seated properly, then tighten up the shock bolt & nut to 70 ft/lbs.

11. Re-install the wheels and safely remove the vehicle from the lift. Take it on a test drive and feel your new suspension. NOTE: It can take several days to weeks for the springs to finally settle. If you are planning to align the vehicle for normal maintenance, then wait until the springs have settled to avoid a faulty alignment. It is always a good idea to have an alignment checked after any major suspension work.


A thorough visual inspection & diagnosis is the absolute first thing that should be done when attempting to fix the air suspension system. Inspecting the system is done to access the overall condition of all the components. Many times an air bag is failed and the dealer or shop says ok its only $300-$400 to fix, you replace the leaking air spring and a few months later the compressor burns out, now it is $2500 to put in a new compressor. The vehicle owner must completely understand all the possible costs involved with a full and long-term proper repair. This is where many Hummer H2 owners decide to convert the suspension to a standard coil spring suspension. If you proceed with repairing the air ride, here is a summary of the instructions, Diagnosing the system is left out as that is very lengthy and would easily be 5-10 pages worth of typing. Also diagnosing this system is not really something a do-it-yourself-er can or should be doing as a bi-directional scan tool, proper DVOM (Digital Volt/Ohm Meter), & wiring schematics are really needed.

1. Identify the type of compressor you have, Typically if you have a 2003-2004 H2, then you probably have a single compressor assembly mounted behind the rear axle. If you have a 2005 -2007 H2, then you have a dual compressor assembly mounted behind the rear axle. If you have a 2008-2011 H2, then you also have a dual compressor mounted behind the rear axle, however it is a different part number then the 2005-2007 models.

2. Now that you know which compressor you have, you can start to figure out what to buy to replace it, General Motors discontinued the single compressor and now requires the 2003-2004 models to be upgraded to the dual compressor setup when a replacement is needed. GM introduced an airline kit that is needed to upgrade the single compressor to the dual compressor. If you need technical support figuring out how which compressor you need, you can call our tech support number at 1-866-770-2771. For all the 2003-2011 models, GM now only offers the complete Dual Compressor assembly. So if you have a single compressor from the 2003-2004 models, you will also need to buy the air line kit. Also assuming you have properly diagnosed the vehicle, you need to consider replacing the control module if it does not come with the particular compressor you are buying. Are you confused yet? The compressor assemblies are called assemblies because they also have the dryer’s, valve bodies, switches, and control module all mounted on one large steel plate, Depending on how or who you buy the compressor from, it may have a control module or may not. Most do not and you will be hit with another $400 if you have to buy a control module.

3. You may also need the Air Spring Bags themselves, another $180-$200 each

4. Hopefully you have the parts you need to proceed and here comes the fun part. First of all, all the factory GM repair manuals for this repair are written for a professional technician that understands wiring schematics and proper repair procedures.

5. Many of the following procedures are really best done the way GM says they should be done, Altering or not using a scan tool to do these repairs can cause unknown and/or difficult to diagnose unintended  problems. If you read the instructions above on how to remove the compressor, then it is basically the same except when you put the new compressor into place and get it all connected, their are some procedures that really must be done with a scanner. These procedures are as follows:

a. Trim Height Calibration Procedure – With Scan tool in hand and connected, go to the air suspension section and under “Special Functions” you can find the calibration procedure, follow the instruction within the scan tool.

b. Air Pressure Pressurization Procedure – Located in the scan tool under “Special Functions”

c. Verify original trouble codes have bee repaired and cycle through the scan tool procedures to make sure all other components are working properly, During the initial diagnostic procedure, it is possible to not realize other failed components unless they set diagnostic trouble codes initially. If for instance your compressor failed, you go ahead and replace it and then you have a new trouble code for a level control sensor or worse a Suspension Control Module(suspension computer or brain). Most of the time a failed Suspension Control Module is found during the initial diagnosis, however if your compressor is failed, then you can not properly test the full functionality of the system  or control module until you put a compressor in it and try to restart the pressurization procedure. In other words, other problem parts are hidden and not able to be diagnosed from the beginning if you cannot get air into the system to check. The vehicle will go through its own process to set the proper ride height after a new compressor or air bags are installed. Hence this is when you discover another part needed that was not able to be identified during the initial diagnosis. This is the reason we say near the beginning of the article that the vehicle owner really needs to know all of the possible costs involved with the normal & continuous degradation of an air suspension system.


Taking a break, more to come soon…………………..

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