A vehicle’s fuel economy, driveability, and emissions, and the condition of fuel system components, are affected by the quality of the fuel in the vehicle’s fuel tank. Two of the factors that define fuel quality may be easily observed and analyzed in your service department -- fuel contamination and amount of ethanol in the gasoline. These will help you diagnose fuel related concerns.

The essential tool Fuel Composition Tester J-44175 (fig. 1), a microprocessor-based handheld device, allows you to accurately analyze gasoline and gasoline/ethanol blends.

IMPORTANT: When using the Fuel Composition Tester J-44175, always observe the safety practices and procedures explained in the user manual, and in SI. Refer to the manual for test procedure details. The following information contains highlights only.

IMPORTANT: The user manual has recently been revised. See details in the accompanying box.

OBTAINING FUEL SAMPLES

You will use a pressure gauge, either J-34730-FF or CH-48027, to obtain fuel samples from the vehicle’s fuel rail pressure connection.

To properly sample fuel, you must first flush out the fuel pressure gage hose that is used to obtain the fuel sample. Any fuel that remains in the gage hose from a previous vehicle must be flushed with fuel from the vehicle being tested.

You will take TWO separate fuel samples from the vehicle. Each sample is tested separately. Perform all testing in accordance with appropriate service information (SI) procedures and applicable diagnostics.

First Sample -- Use the first sample to observe any particulate matter or gross water contamination. Allow the sample to settle for a few minutes and then visually observe for water separation or sediment. The first sample must NOT be placed into the J-44175.

Second Sample -- Only the second sample taken should be placed into the J-44175.

TESTER TIPS

When using J-44175 to test E85 fuel for ethanol concentration, there are several factors which can have an effect on the accuracy of the test reading.

Effects of Humidity -- When testing in high ambient humidity and temperature conditions, it is possible for humidity to be absorbed into the fuel. This can adversely affect your reading. Remember that ethanol will absorb a certain amount of water. There is a connection between the fact that ethanol will easily absorb water and the effect it has on accuracy when testing E85 for ethanol concentration.

TIP: This is the principle used by ethanol-based fuel additives to prevent gas line freeze in the winter. Those products are effective because the ethanol in the additive absorbs water in the fuel.

Depending on the level of humidity in the air and how long the fuel sample is exposed to it, the tester's AC frequency reading may begin to slowly increase. Readings taken after 15 seconds will not be accurate. If the fuel sample sits longer than 15 seconds before it is tested, do not test that sample. Collect a new sample of the vehicle’s fuel and test it within 15 seconds.

Effects of Cleanliness -- Keep the J-44175 as well as the 100mL sampling beaker as clean as possible. Do not use the shop's compressed air to clean any of the surfaces that will touch the fuel sample, including the 100mL beaker, the tester's fuel bowl or test ports. Compressed air may contain small amounts of water or other contaminants. Sweat, fingerprints or other materials can also adversely affect accuracy of the readings.

Effects of Temperature -- The tester automatically compensates for fuel temperature. If the temperature of the fuel is drastically different from the temperature of the tester, the automatic compensation may not react within the 15 seconds required to test a fuel sample. For instance, if the fuel being tested has just been pumped from an underground storage tank, it can be considerably colder than the tester. For best results, a vehicle that has just been filled with cold fuel should be allowed to normalize before sampling.

TIP: Allowing a fuel sample to warm up in the 100mL beaker before being tested is not acceptable because the fuel sample will be exposed to the air for too long, as explained above.

TOOL ACCURACY vs. LABORATORY TESTING

The Fuel Composition Tester J-44175 tool is primarily intended for technician diagnosis and use with SI diagnostics, not analytical testing of fuel samples.

Here’s a brief (and somewhat technical) explanation of the differences between of the
J-44175 test results and those obtained in laboratory testing.

The J-44175 is designed to have an accuracy of +/- 5%, and testing of existing tools in the field indicates that they perform well within that specification. When comparing J-44175 test results with a laboratory test, it is important to understand that the lab reports must be stated in Volume Percent to be meaningful and the lab results typically will be 4%-5% lower than levels you will obtain in the shop (at typical E85 alcohol concentration levels). This is due to the addition of denaturing agents in ethanol produced as a fuel additive in the United States.

TIP: The new, revised user guide for J-44175 and SI both mention that, when using the tester, measured ethanol values between 60% and 91% are acceptable for E85. These figures take the tool’s +/- 5% accuracy into account. DO NOT add another 5% to the 91% indicated by the tool.

So, it is possible for a test result from the J-44175 to be as much as 10% higher than a laboratory report on the same fuel sample. This is an entirely normal and expected result due to the reasons stated above.

TIP: SI diagnostics are designed to work with the J-44175 test results and not necessarily those of a laboratory.

If for some reason you suspect your J-44175 is not reading fuel samples accurately, there is revised tester verification procedure in the new version 2.0 manual which uses acetone as well as the air test previously used. Also, there is a test cell cleaning procedure which uses acetone, if the test cell or fuel bowl should become contaminated. When using acetone for
J-44175 diagnostics or cleaning, always be sure it is fresh acetone from a sealed container.

- Thanks to Ken Peacock and Jack Woodward

REVISED USER GUIDE FOR J-44175 SPX/Kent Moore is releasing an updated user guide for the J-44175 in early 2007 for distribution to all dealers with the J-44175 tool. The new manual is version 2.0 with a yellow cover (fig. 2) and should be placed with the J-44175 when received. All earlier versions of the manual must be destroyed. Take a few minutes to read the revised tool usage and sampling procedures before using the tool. Some of the points you should review from the new manual are: - Tester setup. - Tester verification with air and acetone. - Gage hose flushing. - Importance of testing the second fuel sample quickly because ethanol absorbs moisture from the air. - Taking TWO different fuel samples, with different test procedures for each. - New acceptable levels of ethanol percentage.

Here are some diagnostic tips for use with most vehicles equipped with the Tire Pressure Monitor system.

Tire Pressure Monitor Values Show All Dashes on Driver Information Center ( DIC)

If power is disconnected from the Remote Control Door Lock Receiver (RCDLR) or if the vehicle battery is disconnected, the TPM sensor IDs are retained BUT the tire pressures are lost. This is because the RCDLR cannot assume that tire pressure is maintained over an unknown period of time. The DIC will display all dashes (- - -) and the Tech 2 will indicate the default value (148 PSI). This is normal operation. Driving the vehicle or performing a pressure release (see below) will cause the sensors to transmit, returning the display to normal. Detailed information can be found in SI, in the owner manual, or in PI PIC4296.

TIP: If the system will not reset normally, see bulletin PIC3764N

Pressure Release (Delta P) Method of Sensor Learn (Owner Manual Method)

It takes only a few seconds of pressure release (just over 1 PSI) to activate a sensor. However, when the sensor is stationary, the TPM system is on a 30 second pressure polling cycle time. This means the pressure change may not be transmitted immediately. The time it takes for the system to acknowledge the change (via a horn chirp) is variable and may take up to 30 seconds, so patience is essential.

TIP: It is NOT necessary to continue to release air from the tire until the vehicle acknowledges. Release pressure for 5-10 seconds and then wait for the vehicle to acknowledge with a horn chirp.

J-46079 Tire Pressure Monitoring Service Tool

The J-46079 tool has significant power consumption and drains batteries quickly. If used only for sensor learn procedures, a set of alkaline batteries should last long enough to learn 12 or more vehicles. Carbon (non-alkaline) batteries do not have the current capacity to support the tool's power consumption. Use ONLY 100% alkaline or rechargeable batteries in the tool.

TIP: Just one carbon battery in the tool, mixed with alkaline batteries, will restrict the current flow enough to cause problems with tool operation.

TIP: For further information, see bulletin PIC4296.

- Thanks to Hiram Gahima and Stephen Falko

When lifting or jacking a 2007 GMC Acadia or Saturn Oulook, avoid contact with the Underbody Side Rail (fig. 3). This is for cosmetic purposes only. It hides the exhaust system and fuel tank when the vehicle is viewed from the side.

CAUTION: Besides damaging the Underbody Side Rail, the vehicle could shift on the lift, leading to severe vehicle damage and personal injury.

- Thanks to Jerome Bednarchik

On the 2007 Chevrolet Equinox and Pontiac Torrent, here’s how to remove the Underhood Electrical Center/Junction Block Cover without damage.

To remove the fuse block cover, push in on the four tabs with a flat-bladed tool (fig. 4).

- Thanks to Alex McKay and Karem Youkhana

Owners of some 2003-06 Cadillac Escalade, Chevrolet Suburban and Tahoe, and GMC Yukon models with RPO CJ2 and C69 may have one or more of the following concerns:

- Intermittent ticking/clicking noise from rear HVAC system

- Unable to control rear system temperature

- Unable to change rear system modes

The HVAC actuators may hunt for the correct commanded position. This cycling can cause a clicking or ticking noise.

Overtravel of the HVAC system control doors can cause one or more of the listed system conditions. If overtravel occurs, a DTC sets and the door goes to a preset default position.

When a system door defaults, that door stays at the default position until the code is cleared. Clearing the code allows the door to operate properly until the overtravel condition re-occurs.

Replace the auxiliary (rear) HVAC control module (part number listed in the table below). This module contains a new calibration to compensate for the actuator overtravel condition and the hunting/clicking and ticking noises. The new calibration effectively eliminates both codes B0434 and B3764. The new control module also eliminates the default of the doors associated with the codes. The new control module allows door travel from counts 0 to 255 without setting a code or defaulting the door.

When using the new auxiliary HVAC control module, you may notice a slight increase in rear blower speed (approximately 50 rpm). If the customer comments that the increase in blower speed is objectionable, the blower control module may be replaced with the second design blower control module to correct the slight increase in blower speed.

TIP: The new auxiliary HVAC control module is compatible with both the first design and second design blower control module.

TIP: The revised auxiliary HVAC control module should not be used unless one or more of the codes listed above is set. The revised control module will not correct any other DTC or A/C performance concern.

- Thanks to Dave Roland

This information applies to 2007 fullsize pickups and utilities.

The ABS lamp may light, followed by a Service Stability message in the Driver Information Center. Diagnostic code C0710 is set in the EBCM. And, DTC C0455 may or may not be set.

If, after normal diagnosis, the vehicle is not repaired, turn the steering wheel to the straight ahead position. Check the Steering Wheel Position parameter using the Tech 2 scan tool. If the steering wheel position is not reading zero ( +/- 3 degrees) with the vehicle wheels straight ahead, check that the steering wheel is properly installed.

The alignment arrow on the steering wheel and a mark on the shaft should be aligned
(fig. 5). If the steering wheel is not properly installed, remove the steering wheel and properly align it. Torque to SI specifications. Perform an alignment on the vehicle after the steering wheel has been corrected.

- Thanks to Paul Radzwilowicz

Some owners of an Equinox or Torrent may comment about a liftgate creak or “itch” noise. This condition may be addressed by applying grease to the liftgate latch ratchet (fig. 6).

A Latch Assembly
B Striker
C Ratchet in half-latched position
D Grease

Begin by opening the liftgate and pushing the latch ratchet to the half-latched position
(fig. 7). Then apply a thin layer of grease p/n 26074325 (GM spec 9986108) all around the surface of the ratchet (fig. 8).

TIP: After applying grease, disengage the ratchet to the unlatched position by pulling the liftgate handle.

- Thanks to Angelo Girolamo

Some 2007 Chevrolet Avalanche, Suburban, Tahoe and GMC Yukons equipped with 246EAU Transfer Case (RPO NP8) may exhibit an intermittent Service 4 Wheel Drive lamp and history code C0378 (front axle switch circuit signal invalid).

Inspect the front differential for proper mechanical engagement. Inspect terminal pin tension at the front axle actuator, connector C2 at the TCCM, and C109 and C110. Refer to SI for connector locations.

TIP: Replacement of the TCCM has proven unsuccessful in repairing the intermittent DTC C0378.

- Thanks to Chuck Krepp

This information applies to the 2001-2007 Chevrolet Silverado Classic, GMC Sierra Classic and 2007 Chevrolet Silverado, GMC Sierra.

Some of these vehicles equipped with Allison LCT1000 transmissions do not have PTO gears installed on the rotating housing. Instead, they have a tone ring for the turbine speed sensor that does not have the ability to drive a PTO (power take-off).

1: All 2001-07 8.1 L18 (VIN code G) and 2001-04 6.6 LB7 (VIN code 1) engine equipped trucks will have the PTO gear installed from the factory and has the ability to drive a PTO if desired.

2: All 2004-07 6.6 LLY (VIN code 2), 2006-07 6.6 LBZ (VIN code D), 2007 6.6 LMM
(VIN code 6) and 2007 8.1 L18 (VIN code G) engine equipped pickup trucks will not have a PTO gear installed but will only have the tone ring.

3: All 2004-07 6.6 LLY (VIN code 2), 2006-07 6.6 LBZ (VIN code D), 2007 6.6 LMM
(VIN code 6) and 2007 8.1 L18 (VIN code G) engine equipped chassis cab trucks
(models *C36*** or *K36***) will have a PTO gear installed. Trucks with box delete option RPO ZW9 do not have a PTO drive gear unless they are 2007 and prior model years equipped with an 8.1L L18.

If a customer desires to use a PTO on a pickup truck equipped with LLY, LBZ or LMM 6.6 engine, it is necessary to install a rotating housing that has a PTO gear installed on it.

Part numbers for the rotating housings are:

This repair is not covered under warranty and is done at the customer's expense.

- Thanks to Chuck Krepp

The owner of a 2007 Cadillac Utility equipped with 22-inch factory wheels (RPO P56) may experience loose, missing, or noisy center caps.

This may be due to an improperly installed center cap. Check for proper installation of the center cap. It is possible to install the center cap in several ways, but there is only one correct way to achieve a tight fit.

When installing the center cap, the valve stem icon (fig. 9) should point toward the valve stem of the wheel.

- Thanks to Paul Radzwilowicz

This information applies to 2007 Chevrolet Avalanche, Silverado, Suburban, Tahoe, and GMC Sierra, Yukon, Yukon Denali, Yukon XL, Yukon Denali XL with center console
RPO D07.

The rear center console cup holders may not retain a cup properly when turning or accelerating. The original liners are cup mats with no retention tabs (fig. 10).

To address this concern, replace the cup liners with a new updated one-piece liner p/n 25793661 (fig. 11).

Before installing the new one-piece liner, remove the two tabs (A) located on the front and back of the rubber lining (fig. 12). This provides a better fit and prevents a gap between the liner and the cup holder bezel.

- Thanks to Paul Radzwilowicz

Here’s how to locate unit repair information in SI for the following subjects:

1. 1997-2006 automatic and manual transmissions

2. 1998-2006 transfer cases

3. 2001-02 engines

On the SI home page, under the Select Other Options section, click on Unit Repair. It is not necessary to “build” a vehicle.

On the next page, select the type of component that is to be repaired. For instance: Driveline/Axle

Then select the actual component, by name. For instance: Transfer Case - Steyr.

Next, select the desired category. For instance: Repair Instructions

On the final page, select the specific repair document you need. For instance: Transfer Case Disassembly

TIP: For 2007 model year and onward, the unit repair sections can be found after “building” the vehicle, in the normal service manual section.

- Thanks to Chuck Krepp

The 2007 Silverado Classic and Sierra Classic 2WD 1500 Crew and Extended Cab models with the 5-foot 8-inch box now use torsion bar front suspension.

In the past, these models have always used coil springs. Be aware of this change when comparing the new trucks with past model vehicles for ride, handling, alignment and Z-height concerns.

- Thanks to Jim Will

Some owners of 2007 full-size utilities and pickups with Automatic and Manual Climate Control (RPO CJ2 , CJ3, or C67) may comment of a musty odor from the Heating, Ventilation and Air Conditioning (HVAC) system. This condition occurs most often on initial startup after the vehicle was driven on a hot, humid day. The condition may be caused by condensation build-up on the evaporator core, which does not evaporate by itself in high humidity conditions.

The 2007 full-size pickup trucks and utilities have an option to enable afterblow on vehicles equipped with Automatic and Manual Climate Control. This is different from previous years, where the only way to prevent repeat A/C evaporator core odor concerns was to install an afterblow module kit.

TIP: Do not enable the afterblow function until its purpose and operation are explained to the customer and they approve the change.

Once the afterblow option has been enabled, the blower motor will turn on approximately 10 minutes after the vehicle is shut off. The blower motor will run continuously for 10 minutes at a 30% duty cycle. The afterblow function will activate only if the air conditioning compressor was engaged during conditions of high ambient temperature. If the vehicle is started within 10 minutes of the last key off, the afterblow function from the previous key cycle will be cancelled.

Turn this option ON in the HVAC Control Module instead of installing the Electronic Evaporator Dryer Module Kit referred to in the Air Conditioning Odor bulletin 99-01-39-004A.

To enable afterblow:

1. Verify the Tech 2 is updated with the latest software.

2. “Build” the vehicle on the Tech 2.

3. Use the following Tech 2 pathing:

Vehicle Control Systems > Select engine > Module Setup > HVAC Control Module > Afterblow Option

4. Follow the on-screen directions.

- Thanks to Paul Radzwilowicz

Some owners of the new 2007 Chevrolet Silverado and GMC Sierra may have questions about whether pickup box accessories will carry over from the Silverado Classic or Sierra Classic to the new trucks.

In general, the following accessories should carryover (depending on manufacturer):

- Tonneau covers

- Pickup box caps (may have styling or color differences)

- Accessories attaching to side bed rail flange

- Accessories attaching to a single stake pocket

Here are some dimensional comparisons between the boxes
(fig. 13 Top View and fig. 14 Side View):

A. The new box has a 40mm increase in height from the load floor to the top of the side bed rail in the rear.

B. The new box has a 30mm increase in height from the load floor to the top of the side bed rail in the front.

C. The front stake pocket location is 52mm rearward compared to the Classic truck box.

D. The middle (if equipped) and rear stake pocket locations are unchanged.

E. The distance across the truck (side to side) between the stake pockets is unchanged.

F. The stake pocket size is unchanged.

G. The distance between the wheel wells is 25.3mm wider on the new box.

H. The side bed rail attachment flange is unchanged.

J. The top view opening of the box is unchanged with one exception. The fore/aft length is shorter by 33mm due to a change in the front panel flange.

- Thanks to Jim Will

This information applies to the Equinox and Torrent.

Here is a description of the features in these vehicles that are controlled by the Remote Start. Upon activation of the RKE, these features will operate as listed until the ignition key is turned on, or the system times out.

* There are future plans to add a feature that turns the heated seats ON if outside air temperature is below 5° C (41° F).

- Thanks to Angelo Girolamo

This information applies to 2005-07 Cadillac Escalade, Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe, GMC Sierra, Sierra Classic, Yukon with Regulated Voltage Control (RVC).
Some customers may comment that the voltmeter fluctuates between 12 and 14 volts. Starting with the 2005 model year, light-duty full size pickups and utilities are equipped with a Regulated Voltage Control (RVC) system. See TechLink September 2004 for the full story.

The RVC system controls voltage based on such parameters as battery state of charge, battery electrolyte temperature, battery current, and electrical loads. This causes the voltmeter to fluctuate between 12 and 14 volts. (Non-regulated systems usually maintain a more consistent reading of 14 volts.)

This fluctuation with the RVC system is normal system operation and no repairs should be attempted.

Refer to the owner manual Section 3 (Instrument Panel) Voltmeter Gauge for more information.

- Thanks to Jim Will