The CH-48027 Digital Remote Pressure/Vacuum Gauge is an essential tool released in January 2006 (fig. 1). As time passes, demands for more precision and reliability have been placed on fuel system operation. This has increased the need for proper, time-efficient, and accurate diagnosis.

Diagnostic tools are constantly being evaluated to determine if their use will enhance diagnosis. The CH-48027 Digital Remote Pressure/Vacuum Gauge was determined to provide superior accuracy when measuring fuel system pressure. The digital readout is far easier to read with precision, compared with an analog gauge. It is far more robust, and offers increased safety because it eliminates the need to route pressurized fuel out of the engine compartment to a remote mechanical gauge.

A digital pressure transducer/sensor passes information to the gauge over a 12 foot cable (3.6 m). This enables you to read the gauge from inside the vehicle while fluids remain outside. There is no need to hang a gauge from the window or worry about fluid leaks.

But the CH-48027 Digital Remote Pressure/Vacuum Gauge is much more than a fuel pressure tester. Here are some tips for getting the greatest value from this versatile and useful tool.

The gauge can be adapted to most popular pressure test kit fittings and can even be adapted to a standard air chuck for tire pressure testing. It's useful for testing practically any system that calls for a pressure or vacuum reading. You can use it to test:

-  Fuel systems on both gasoline and diesel engines

-  Engine oil pressure

-  Cooling system pressure

-  Cylinder compression (with adapter)

-  Cylinder leak down (with adapter)

-  Tire pressure testing / TPMS systems

The tool's Min/Max feature helps identify intermittent conditions by capturing road-test pressure drop-outs.

Because the large back-lit LCD can be set to display in PSI, KPA, BAR and in. Hg., there's no need to convert measurements. The tool is E-100 compatible, so it can be used with all commercially available fuels, as well as oils.

TIP: Battery life will be prolonged if the back-light is used sparingly.

The all-aluminum case is drop-resistant and the digital readout has no mechanical parts to go out of calibration, so the CH-48027 is more robust than analog gauges.

KIT CONTENTS

-  Remote digital pressure gauge

-  Bleeder valve assembly

-  Fuel rail access fitting

-  Oil pressure adapter

-  Diesel adapter

-  Storage case

-   Replacement seals

WORKING PRESSURES

The gauge has an accuracy of +/- 1% of full scale reading.

USER TIPS

Be sure to refer to the user guide supplied with the gauge.

Be sure the gauge has been properly zeroed before using the first time, after replacing batteries, or if the readout does not indicate zero with no pressure or vacuum applied. The manual explains how to do this correctly.

The readout can be set to display the real-time value (NORMAL), the lowest value read (MIN), or the highest value read (MAX).

TIP: The gauge beeps once when the MIN or MAX value is updated.

MIN/MAX is automatically cleared when the gauge is turned off. While the gauge is on, MIN/MAX can be cleared using the Display Mode button.

- Thanks to Kevin Suhajda

Bluetooth® technology will be available on most General Motors vehicles beginning in model year 2009 as either optional or standard equipment (see February 2008 TechLink). The Bluetooth functionality will be accessed via the OnStar Module.

The available GM Bluetooth Test Tool (fig. 2), 453-U260-000-R, tests only for valid pairing confirmation between the vehicle and customer’s approved cellular phone. This allows you to diagnose and differentiate between the vehicle’s Bluetooth transmission pairing via the Onstar module and the GM-approved Bluetooth cellular phone.

BLUETOOTH TEST TOOL FEATURES

- USB 2.0 Bluetooth Adapter enables wireless capabilities to be added to a USB desktop or notebook computer. Allows cable-free connections to other Bluetooth enabled devices (cellular phones).

- Frequency Band/Bandwidth: 2.4 GHz range

- Compatible with all Bluetooth v1.1, v1.2, and 2.0 devices

- AFH (adaptive frequency hopping) eliminates interference

- 128-bit secure data encryption for safe communications

- GM Dealer Terminal Approved (Software).

TIP: In order to work, the cellular phone must be paired to the vehicle. Up to five devices can be paired to the vehicle at one time, but only one can be connected at any given time.

The GM Bluetooth Tool p/n 453-U260-000-R is available through GM Dealer Equipment. http://www.gmde.net/index.cfm

- Thanks to Katul Patel

The 2008 Astra has black plastic wheel bolt covers that can be difficult to remove (fig. 3).
The covers are installed during the vehicle PDI.

To remove the bolt covers, the owner should use the flat-blade screwdriver provided with each vehicle in the trunk tool kit. Gently pry the covers off. A rag should be used to protect the surface of the wheel while prying to prevent accidental scuffing.

Technicians may use fine-tipped needle nose pliers or similar. Be careful not to damage the wheel finish. To remove covers using needle nose pliers, carefully grip covers from the front to avoid damaging the wheel, and pull straight out.

TIP: The covers do not twist or screw off.

- Thanks to Jeff Gorenflo

Here's an explanation of how to differentiate the VIN of a 2007 model year Silverado/Sierra "Classic" Full Size Pickup (GMT800) from the VIN of a Silverado/Sierra Full Size Pickup (GMT900). Service Information and Parts Catalog information references only "Classic" models.

Both are 2007 model year vehicles and have similar VIN characteristics. The distinction is made in the sequence numbers.

- Thanks to Steve Love

On a 2007-08 Sierra and Silverado with the base I/P, the ashtray may not close properly (fig. 4). The pivot on one side of the ashtray may come off the pivot bar.

It is not necessary to replace the entire assembly. A new service p/n 25918822 (package
of 2) is now available for the pivot ("eagle claw"). Simply slide out the original pivot and slide a new part into the T-slot on the bottom side of the ash tray (fig. 5).

A  T-slot

B  Replacement pivot

- Thanks to Mike Pedrie

Some owners of a 2008 Cadillac CTS may experience a creak noise coming from the rear underside of the vehicle, especially at low ambient temperatures. The cause may be the rear suspension toe adjustment link inner and outer bushings (fig. 6). The noise is produced by the relative motion between the outer flange of the bushing and the outer can of the link.

Characteristics of the rear suspension toe adjustment link bushing noise:

- Coming from under the rear of the vehicle.

- Occurs when the vehicle is driven over bumps, curbs, or twist ditches, events where the rear suspension sees medium to large amounts of vertical travel/motion.

- Squeak, creak, or squawk.

- Gets worse in cold weather.

- Might go away if the bushing is wet (for instance, if the vehicle is driven in the rain).

Application of GM Super Lube to the bushings can reduce or eliminate the noise until a re-designed toe link assembly is available.

1. Raise and support the vehicle.

2. Hold a piece of paper or cardboard between the toe link outboard bushing and the brake rotor/caliper to prevent overspray of lube onto the brake rotor/caliper. If necessary, remove the tires and wheels.

3. Spray GM Super Lube (p/n 12346241) (10953474 in Canada) on the flanges of the outboard toe link bushing, both at the knuckle-side and the bolt-head-side of the bushing (fig. 7).

Use enough Super Lube to cover the bushing flanges (in circles).

4. Spray Super Lube on the flanges of the inboard toe link bushing. Use enough Super Lube to cover the both of the bushing flanges.

5. Install the tires and wheels if removed.

6. Remove the support and lower the vehicle.

- Thanks to Michael Ciarkowski

The rear axle carrier assembly on the 2008 Cadillac CTS includes a mass dampener assembly (fig. 8). If the rear axle carrier assembly is replaced for any reason, remove
the mass dampener and bracket from the original unit, and install it on the new axle.
For additional information, see SI Document 2030230.

IMPORTANT: If the dampener assembly is not installed on the new axle, a driveline noise or vibration will result at approximately 55 to 65 mph (90 to 105 kph).

- Thanks to Rich Burrell

This information applies to the 2008 Tahoe and Yukon equipped with the Two-Mode Hybrid RPO HP2.

Engineering is asking you to capture and save freeze frame data records of hybrid DTC
and driveability issues. This information will help improve diagnostics and increase the understanding of root causes.

Engineering needs to capture freeze frame records from the HPC Hybrid Powertrain Controller or HPCM as well as any other powertrain control modules that have stored
DTCs.

Engineering is asking for your assistance for the duration of the Launch Action Center. Technical Assistance, Action Center Manager, or Engineering may be asking you to email the freeze frame records to assist in diagnosis and repair of hybrid vehicles.

It's important to save this data until it's requested. Save the data using the capture info option in the Tech 2. Download the data to TIS2Web just as you would a snapshot. Then, using the e-mail function in TIS2Web, send the data to whomever requests it.

IMPORTANT: Data capture needs to occur before clearing codes or disconnecting the 12v battery or discharging the 12v battery.

On the subject line, include the code number and module it was pulled from. Engineering is interested in ALL codes in the hybrid and powertrain system. It may take multiple e-mails to send all the information.

- Thanks to Chuck Krepp

This information applies to the 2008 2-mode hybrid with RPO HP2.

Starting February 4, 2008, the following parts are on parts restriction through the GM Technical Assistance Center:

The Electronic Brake Control Module (p/n 25909777) and the Brake Pressure Module Valve Assembly (p/n 15879113) for the Hybrid vehicles are also on restriction, but must be ordered through the PQC after following special instructions. (Refer to PIT4383C for special instructions on ordering one of these two parts)

- Thanks to Paul Radzwilowicz

On 2-mode hybrid vehicles, the brake system does a brake circuit leak check/relearn at every Key Off. This process takes about 30 seconds. If the 12V battery is disconnected before the completion of the brake circuit leak check/relearn, on the next power-up, the brake system will default to the Fail-Safe System Operation mode.

TIP: Complete details are available in SI under Battery Negative Cable Disconnection and Connection, and the Antilock Brake System Description and Operation for these vehicles.

- Thanks to Stephen Falko

Some owners of a 2008 Tahoe or Yukon equipped with the two-mode hybrid option may comment that the Auto Stop function does not operate at all in hot or cold temperatures or takes a long time to activate in cold ambient temperatures. Customers may also comment that fuel economy is less that expected. This concern may be considered a normal condition with certain conditions and driving maneuvers.

Inform the customer that environmental conditions and driving habits have a direct correlation with fuel economy. The Auto Stop mode may not be enabled if certain hybrid and vehicle components are too hot or too cold.

In winter, the hybrid battery module temperature, engine coolant temperature, transmission fluid temperature, and cabin temperature must be warmed up before Auto Stop is allowed. The hybrid controllers also monitor ambient temperatures and interior temperature along with the above mentioned criteria to determine desired Auto Stop conditions.

In cold temperatures, the Auto Stop criteria are highly dependent on the outside air ambient temperature. Depending upon the overnight soak time, specific drive cycles, and the factors listed above, it may take an hour before the first Auto Stop occurs. In the summer, the hybrid batteries, the hybrid cooling system and the engine must all be kept cool for Auto Stop mode. Running the interior air conditioning and keeping the hybrid battery vents unrestricted will help keep the hybrid batteries cool.

Heavy acceleration requires more engine operation and thus more fuel consumption. Heavy braking does not allow regenerative braking to occur. Fuel economy will be the same as a base truck under heavy throttle and brake apply. Adjusting both braking and acceleration driving habits will result in the highest system efficiency. Refer the customer
to monitor Active Fuel Management (AFM) information on the Hybrid Navigation/Radio Display Screen or the efficiency gauge to learn driving habits and conditions that improve fuel economy. This includes trying to keep the efficiency gauge in the green zone as much as possible and try to drive in 4-cylinder mode as long as possible. The transmission gear shift selector should be placed in Drive and not in manual for best fuel economy. Auto Stop is inhibited in the manual transmission shift ranges.

Additional tips to improve fuel economy include keeping tires properly inflated, accelerating to allow for as much Mode 1 electric propulsion as possible, limiting the use of remote start, reasonable highway speeds, minimizing carrying unnecessary cargo or mass, and keeping the transfer case in 2WD instead of Auto for best fuel economy.

If there are no DTCs found in the vehicle modules that would prohibit Auto Stop and the hood switch reads correctly, this condition will be considered an operating characteristic. You can monitor the HPCM (Hybrid Powertrain Control Module) and "Auto Stop Inhibit Reasons" data list to identify the normal inhibit reason.

- Thanks to Chuck Krepp

This information applies to 2007-08 fullsize utilities and pickups with Stabilitrak
(RPO JL4) and 2008 fullsize 2-mode hybrids with blended brakes (RPO J92).

Since May 2007, the EBCM and BPMV components on utilities and pick-up trucks with Stabilitrak (RPO JL4) have been on parts restriction.

Starting on February 4th 2008, the EBCM and BPMV for the 2-mode Hybrid vehicles are on restriction.

Refer to PIT 4383C for parts lists and details.

Be sure to fill out the template in the bulletin before contacting PQC at 1.866.654.7654 when attempting to order affected parts.

- Thanks to Paul Radzwilowicz

This information applies to the AURA, VUE and Malibu Hybrid vehicles. The polarity symbol embossed onto the top of the battery DOES NOT indicate the polarity of the adjacent battery cable terminal. Here's why.

A hybrid battery pack consists of six individual batteries, arranged in three groups with two batteries each.

The terminals of the six individual batteries are located on their ends. The polarity + and - symbols embossed onto the tops of the battery cases refer to the battery terminals on the ends of the batteries (fig. 9).

A  Negative symbol

B  Negative terminal on end

C  Positive symbol

D  Positive terminal on end

Each pair of batteries is connected in parallel. The positive terminals of each pair are joined by a metal bus, and the negative terminals of each pair are joined by another metal bus
(fig. 10). The metal buses extend above the top of each battery, and a battery cable attaches to a post on each bus.

A  Positive bus

B  Negative bus

On each battery top, one symbol is visible and one symbol is obscured by the top of the bus (fig. 11).

A  Visible symbol

B  Obscured symbol beneath

IMPORTANT: The symbol that is visible on each battery DOES NOT indicate the polarity of the cable terminal adjacent to it. In fact, in each case, the symbol showing on the battery top is THE OPPOSITE of the polarity of the cable terminal adjacent to it.

Figure 12 shows the locations of the + and - cable terminals and cable routings.

- Thanks to Jason Collins

This information supplements an article in the March 2008 TechLink entitled Engine Running With Key Turned Off, which involves voltage on circuit 5985 with the key turned off. The condition described below can be a cause of this voltage.

The owner of an Acadia, Enclave or Outlook may comment that the engine continues to run after the ignition is turned off, or that the engine will not start. This may be the result of water intruding into the instrument panel (IP) BEC. Before proceeding with other diagnosis and repairs, here are some suggestions.

Water from the right front sunroof drain hose exits the vehicle (fig. 13). If it then re-enters the vehicle through the front of dash sheet metal, it can drip from the right side dash onto the IP BEC.

A   Water exits through drain hose

B   Water reenters and drips onto IP BEC from sheet metal

The seam must be properly sealed between the plenum upper and plenum reinforcement. This may be inspected from underhood through the opening in the cowl panel (fig. 14).
If there are voids in the bead of sealant, use medium-bodied sealant p/n 12378500 to reseal.

The area to be sealed may be reached through two openings, and the seam must be sealed for its entire length (fig. 15).

A   Access opening

B   Access opening

C   Length of seam seal

TIP: Sealant may be applied with the fingertip or with a plastic trim tool.

- Thanks to Gary McAdam

The 2008-09 CTS and 2008-10 STS with the HFV6 LLT (VIN code V) use an auxiliary vacuum pump to provide adequate vacuum for brake assist at vehicle start-up. The pump is mounted to the front of the engine (fig. 16). It is controlled through a relay energized by the ECM during catalytic heating.

The electric vacuum pump is controlled by the following components:

- ECM

- Relay (part of engine harness)

OPERATION

The electric vacuum pump can be activated only when catalytic converter heating is active. Catalytic converter heating runs only during cold engine startup and is activated up to 60 seconds. Because engine vacuum is reduced during catalyst heating, the electric vacuum pump is activated when necessary.

The vacuum pump runs when the following conditions apply:

- When catalyst heating is on and the driver's foot is on the brake pedal

- The vacuum pump will continue to run as long as the driver's foot is on the brake pedal.

- When the brake pedal is released and catalyst heating is still on, the vacuum pump will continue to run for approximately 5 seconds and then shut off.

The vacuum pump is turned off whenever catalytic converter heating ends.

DIAGNOSTIC CHECKS FOR HARD PEDAL SYMPTOMS

1. Disconnect the engine wiring harness from the vacuum pump.

2. Using a 20A fused jumper, apply 12 volts and ground to the pump.

3. If the pump does not run, replace the pump.

4. If the pump runs, perform the following steps:

- Check the vacuum pump fuse.

- Inspect the wiring harness between the vacuum pump and the ECM for damage, possibly causing a short, blowing the fuse or relay.

5. Check the vacuum brake booster hose, check-valve, and tee for a restriction and/or damage

6. Internal check-valves are located in the hose, one between the tee and the engine, and one between the tee and the pump. Check for proper function (air flow toward engine and pump but not toward tee).

Additional information is available in SI through Symptom and DTC P258A-P258D diagnostics located in the Hydraulic Brakes section.

- Thanks to Bob Sasina, Sam Melnyk, Tom Baptist and Tim Pierce

This information applies to the 2007-08 Outlook, Acadia and 2008 Buick Enclave with Automatic HVAC Control Head (RPO CJ2). Some customers may comment that various functions are inoperative or not working properly when selected from the HVAC control head.

Check the connectors at the back of the controller. When diagnosing a vehicle for a HVAC concern, check the grey connector (J3 connection as marked on the back of the control head) for proper installation. If normal function of the controller returns after removal and fully seating connector J3, do not replace the control head. Continue diagnosis only after first insuring that this connector is properly seated into the control head.

- Thanks to Gary McAcam

Some owners of a 2007-08 Escalade, Avalanche, Silverado, Suburban, Tahoe, Sierra, or Yukon may experience a pop or tick type noise from the left front dash area when driving over bumps. The noise may occurr when backing out of a parking spot or going over small speed bumps in a parking lot. The noise is worse when the vehicle is cold and may go away at higher temperatures.

The condition may be caused by a loose spot weld that attaches the L-bracket from the left inner fender panel to the front bulkhead (fig. 17).

Add three bolts with nuts through existing holes in the left fender bracket and the fender inner panel (fig. 18). The fender bracket is spot welded to the inner panel and attaches to the front-of-dash with two nuts and studs through the dash panel.

- Thanks to Paul Radzwilowicz

This information applies to 2007-08 C/K trucks with no-starts, intermittent electrical issues, and battery charging issues. The vehicle does not have issues with parasitic current draw.

Check for proper torque on the passenger side nut of the 175 amp mega fuse during the diagnostic procedure (fig. 19).

A  Passenger side nut

The torque specification is 9 N-m or 80 lb-in. If the nut has lost torque, check for corrosion on the fuse, cable and stud (figs. 20 and 21).

A  Corrosion on stud with loose nut

B  No corrosion on stud with tight nut

TIP: The mega fuse nut torque concern does not apply to the Hummer H2, which has different electrical architecture.

- Thanks to Steve Love

Some owners af a 2006 Rainier, TrailBlazer, Envoy or Saab 9-7x may comment that after the vehicle was serviced, the automatic headlamps do not turn on until the shifter is placed into gear (out of the Park position) or manually with the switch on the instrument panel.

This may occur if the BCM was replaced. The service BCM for most 2006 model year vehicles reflects the automatic light operation of 2007 model vehicles. This allows the automatic headlamps to turn on only when the shifter is placed into gear or when using the manual switch.

This is normal operation. Compare with a 2007 model or newer vehicle if necessary to show the customer this new operation is normal.

- Thanks to Dino Poulos

This information applies to 2007-08 Escalade, Avalanche, Suburban, Tahoe, Yukon, Acadia, Outlook and 2008 Enclave and Hummer H2.

The GM Accessories Portable Overhead DVD Player may not release from the docking station if the vehicle battery is low and the DVD player's battery is discharged.

Ensure the vehicle battery is charged and the ignition switch is in the run position. The DVD player battery will charge from the vehicle electrical system only with the key in the run position. Charging the DVD player battery may take up to 3 minutes before sufficient charge is reached to allow the DVD player to be disconnected from the docking station. Once sufficient battery charge is reached, the portable DVD player should eject from the docking station. Do not manually force the DVD player from its docking station.

- Thanks to David Wells

On a 2006-08 Pontiac Vibe, the Tech 2 may display a "waiting for data" message on the screen when using software versions 27.011 and 27.012 to check the PCM for DTCs.
The Freeze Frame/Failure Records and PCM Data Lists should function normally.

If this is encountered, update the Tech 2 with Software Version 28.001 or greater and re-evaluate the concern.

- Thanks to Jamie Parkhurst