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Update: GM's Law Enforcement Product Council

GM Fleet’s legendary Earl Gautsche kicked off the spring 2006 meeting of the GM’s Law Enforcement Product Council with an update on service items and the technical changes from 2006. His first emphasis was on the “Change Engine Oil” light. GM’s Oil Life System is used on both the Impala and Tahoe.

Per the owner’s manual, fleets are to change the oil and filter only when the “Change Engine Oil” light is displayed in the Driver Information Center on the dash. Changing oil based on the Oil Life System algorithm, rather than changing the oil at a fixed interval of 3,000 miles, will save money, oil filters and labor. And this practice is specifically covered by the powertrain warranty.

Some departments may be able to push the change interval out to as much as 7,000 miles on patrol cars and 12,000 miles on admin cars. The caveat here is that the brake pads may now need attention before the oil. This is quite a reversal, since many agencies routinely check brake pad wear during the oil change. They may now change the oil during brake pad inspection!

One aspect of the engine oil is NOT covered by the powertrain warranty...running the engine out of oil. All engines use some amount of oil as a normal part of the combustion process. Engines in severe service, i.e., engines in police use, use slightly more oil than engines in retail use. It may be normal for the police engine to use a quart of oil every 1,500 to 2,000 miles. OIL MAY NEED TO BE ADDED BEFORE IT IS TIME TO CHANGE THE OIL. The oil level must be checked on a periodic basis to keep it at the proper level.

2007 Police Impala

For 2007, the police Impala is mostly a carryover from the major redesign in 2006, with three exceptions. First, the 240 hp, 3.9L V-6 has been upgraded with Active Fuel Management (AFM). This is the new term for Displacement On Demand.

With AFM, under light engine loads or steady throttle, three cylinders may shut down to safe fuel. This is accomplished by two-position hydraulic valve lifters. Under certain conditions, AFM disengages the lifters on three cylinders. The 3.9L V-6 becomes a 2.0L Inline Three. Used on larger V-8 engines for some time now, this is one of the first applications of displacement on demand for a smaller V-6.

As a reality check, GM Fleet was quick to point out that AFM may not produce the same fuel economy gains in police use as in retail use. First, most patrol officers drive harder, i.e., heavier demands on engine, than most retail drivers. Second, unlike the bigger V-8 engines, the smaller V-6 may not produce enough torque to run in the AFM mode on all occasions. Admin use of the police Impala may see the fuel benefit, while patrol use may not.

As an aside, the 2006 version of the 3.9L V-6 used a novel intake system—long intake runners for more torque at lower engine speeds and short intake runners for more horsepower at higher engine speeds. A computer-controlled flap regulated which intake system would be used. While a great idea, a throwback to the horsepower race of the late-1950s, these short and long “ram” tubes have been eliminated for 2007.

The sophisticated variable valve timing can provide complete engine tuning throughout the entire rpm range. The variable valve (cam) timing on this 3.9L V-6 is also a first for a pushrod engine, making this quite an advanced powertrain.

Two other minor changes were made to the police Impala for 2007. The heavily-marbled wood (appearing) interior trim has been replaced by a brushed aluminum trim. No kidding now...some people complained that the wood trim, which is more prominent on the redesigned 2006 Impala, made the car appear too fancy and expensive for police service.

Also for 2007, the Content Theft Alarm is now available and designed right into the vehicle. This feature requires the remote start option.

Planning cycles in the auto industry are quite long. That means NOW is the time to make suggestions for improvements to the police Impala. Contact any GM government account manager or Bruce Wiley, product and marketing manager, Law Enforcement Programs, GM Fleet and Commercial Operations at What changes would make the Impala the perfect police vehicle...drivetrain, chassis, interior, trunk, electrical system, whatever?

Tahoe 2WD and 4x4

For 2007, the Tahoe has been significantly restyled and redesigned. It has a more powerful, new generation 5.3L V-8 (320hp vs. 295hp). The more powerful engine is now equipped with Active Fuel Management (AFM). This same AFM system is also used on the 2007 Tahoe, converting the 5.3L V-8 to a 2.7L V-4. Again, AFM may not activate as frequently on a patrol-driven Tahoe as a retail-driven one. When it does activate, the Tahoe produces a different exhaust tone.

The new Tahoe uses the same 160-amp alternator with automatic idle boost as is found on the police Impala. The Tahoe also comes with a 730 CCA battery and auxiliary air-to-oil coolers. The Tahoe has a 100-amp power supply in two places, in the passenger compartment and in the cargo area. All-power harnesses plug in and work the same way on the Tahoe as on the Impala.

For 2007, the Tahoe uses 17-inch steel wheels (1 inch larger diameter than 2006) and is equipped with 70-series, H-rated, Goodyear Eagle RS-A tires. The new Tahoe has a wider track (3 inches more in front; 1 inch more in rear).

While the retail version of the 2007 Tahoe has been available since early spring, the police package version will not be built until November or December. Pricing will be available in June or July. Detailed coverage of the full production 2007 2WD police Tahoe PPV, including driving impressions, will be in the November issue of LAW and ORDER.

Tahoe E85 Compatible

Also new for 2007, both the 2WD, pursuit-capable Tahoe PPV and the 4X4 special service Tahoe 5W4 are now E85-capable. Both Tahoes use the same LMG 5.3L V-8. They can run on straight gasoline, straight E85 ethanol or any combination of these two fuels.
GM Powertrain recently changed the method of determining the alcohol content in the fuel in E85 compatible vehicles. For the 2006 and 2007 models, E85 vehicles no longer use an alcohol sensor to determine the alcohol content of the fuel and make engine adjustments. Instead, the vehicle continuously calculates the alcohol content of the fuel (the exact mixture in the tank at any one time) through a combination of assumptions and measured adjustments.

First, it assumes that the fuel added to the tank will be either gasoline or gasohol with an alcohol (ethanol) content between 0% and 10%. Or the added fuel will be E85 fuel with an alcohol content between 70% and 85%. A minimum of 3 gallons of fuel must be added at any one “fuel event.”

After the refueling event, the system registers the amount of fuel taken on board, and the O2 sensor determines whether gasoline or E85 was added. Based on that, the engine computer makes a major adjustment based on the exact ratio of gasoline and E85 now in the tank. The O2 sensor continues to make ongoing minor adjustments.

The E85-compatible vehicle can be switched back and forth between gasoline and E85 without drivability issues. It takes about 10 minutes or about 7 miles for the vehicle to comprehend and calculate the composition of the new blend in the tank. The use of straight gasoline or straight E85 does not involve a transition period.

As in 2006, the 2007 retail (non-police) Impala with the 3.5L V-6 is E85 compatible. The police Impala with the 3.9L V-6 should not use E85.

Crash Safety

One upfit note on the 2006, and now 2007, police Impala. In addition to the five-star front impact crash rating, it also has a five-star side impact crash rating. Part of the reason is the side airbags. Another reason is the structural tube design under the front seats. Yet another factor is the center tunnel crush box located between the seats.

Removing the cup holder, you will find a label reading, DO NOT REMOVE on this crush box. This is an important component of the side impact structural integrity. Don’t remove it!

Of course, any discussion of side airbags leads to the upcoming FMVSS requirement for side curtain, or roof rail, airbags...and their interaction with prisoner partitions. Side curtain airbags and traditional prisoner partitions are not compatible. Nor has the federal government granted an exemption for emergency vehicles. Side curtain airbags will be standard equipment, and cannot be deleted, for the 2009 model year.

Setina currently makes a side curtain compliant partition. This has modified, i.e., lower, mounting points on the B-pillar. The airbag deployment zone uses a thin, flexible plastic, which yields to the opening airbag without rupturing the airbag.

Heads up. This serves as a split screen only. It is not a thick piece of polycarbonate. It will not stop a forced breach. Just have the officers handcuff their prisoners like they are supposed to do, and all will be well. This Setina partition is currently is use by the New York Police Department.


On an upfitting note for 2007, the police Impala and police Tahoe will share complete electrical systems. Everything is the same from the alternator to the wiring harness. All of the wiring features have the same fit and function. Both vehicles can be upfit exactly the same way.

A great deal of upfit information is available on GM Fleet’s Web site. However, it doesn’t have a separate, stand-alone upfitter’s or modifier’s manual like Ford and DaimlerChrysler. Expect an online version of exactly that, with unrivaled detail, by the time the 2007 police Tahoe hits the street. This will be similar to the info found at for the heavier trucks.

In the time being, contact Brad Baker at Kerr Industries
( for any upfitting questions. In fact, train-the-trainer classes are in the works for upfitting. The one- and two-day classes are planned for both the Oshawa, Ontario (Impala) and Arlington, TX (Tahoe) Kerr facilities. Contact Baker with particular items of interest or emphasis.

Tire Testing

The LEPC meeting included a tour of GM’s tire development center at the Milford Proving Grounds. When the Tire-Wheel System group is done, the tire that meets Tire Performance Criteria specs will operate at the top speed of the vehicle for more than a tank of gas.

With a retail tire, a great deal of emphasis is placed on ride and comfort, noise and fuel consumption. With a police tire, the focus is on braking, high-speed operation and cornering with a special emphasis on shoulder wear. In fact, surviving 32 laps at Grattan Raceway (MSP) and a similar test on the Pomona Fairgrounds (LASD-LAPD) is so difficult that other aspects of police tire performance are traded off to get better outside shoulder wear.

The tire approved for police use on General Motors vehicles is not just any all-season radial with a suitable speed rating. Compared with a retail-oriented all-season tire, the police package all season has a little better dry traction, better wet traction and much better cornering ability. Likewise, compared with a typical all-season tire, the police package tire has less initial tread depth, greater rolling resistance (less fuel economy), heavier weight (more unsprung mass), a stiffer sidewall (stiffer ride) and much less snow traction.

In the case of a police tire on a FWD car, i.e., the Pirelli P6 Four Season on the Chevrolet Impala, the tire must have even more abrasion resistant tread with even more solid tread blocks. The tire must do both the most of the cornering and also provide the most traction during both acceleration and braking. The average, retail, speed-rated, all-season tire will definitely not perform as well on the police Impala as the Pirelli P6.

While a tire developed for a RWD police sedan (Eagle RS-A Plus) may physically fit on the Impala, it was not designed for these dual duties demanded of a FWD police sedan. A tire designed for a FWD police sedan has a different Tire Performance Criteria than one designed for a RWD police sedan.

The GM battery of tire tests includes dozens of both industry-standard and GM-proprietary tests...force and moment testing (handling and cornering), residual aligning torque (pulls and leads), rolling resistance (this is 30% of fuel economy), braking and acceleration traction, snow traction, wet traction, uniformity, noise, load carrying, weight (mass of tire, where less unsprung weight is better), revolutions per mile, high speed capability, air-retention properties, electrical resistance (the tire is supposed to conduct electricity to ground the static charge), tread wear and grooved road wandering (on roads with ¾-inch grooves to lessen aquaplane and reduce noise).

On-car testing includes extensive ride and handling tests and also snow and wet handling on special test tracks with controlled road surfaces and water depths. The centerpiece of the GM tire testing program, however, is its proprietary Accelerated Tire Endurance (ATE) test.

Unique to GM, the tire is tested at maximum load, at certain tire pressures, at various speeds and road surfaces for a high number of miles. It must complete this harshest of all tests without a tire failure. The ATE simulates a “life of tire” test. A tire that earns the GM “TPC” number molded into the sidewall may have gone through the industry’s most severe and complete testing.

The validation testing on the Pirelli P6 Four Season used on the police package Impala resulted in a 1-inch thick binder of documents and test results. The real question is not, “How does GM test police tires?” Instead, “How does the police department test tires before putting something different than the OE tire back in the car?” Keep that in mind when you order a set of cheap retail all-season tires from the local Tires “R” Us.

In the early-1990s, tire-wheel systems got responsibility for all GM wheels. Three of the critical wheel tests are 1) rotary fatigue due to cornering forces, 2) radial fatigue due to heavy vertical loads and 3) biaxial fatigue. The biaxial test flexes the center section of the wheel back and forth like going around a figure-eight track. This test of the flex on the center (spider) of the wheel was instrumental in improving the wheel on the mid-1990s LT-1 Caprice police car. Of course, one of the more obvious but still necessary tests is the wheel impact test. This simulates driving over large pot holes and running into curbs.

How to Test a Police Vehicle

Quite a bit of time was spent discussing ballast in the Tahoe during testing. Officers now have room to carry a lot of they are doing so! The initial estimates of 450 pounds of cargo are being re-evaluated. And questions are being asked.

What happens when 600 to 800 pounds of cargo is carried in the Tahoe? Should the Tahoe be tested with 450, or 600, or 750 pounds of ballast? Right now, the Michigan State Police tests are conducted with no cargo ballast. This year, the Los Angeles County Sheriff tested the Tahoe with a 400-pound cargo ballast.

These are significant questions. Such a trunk or cargo ballast in either an SUV or sedan changes both the low-speed and high-speed handling. While it obviously slows the acceleration, a heavier vehicle also taxes the brakes more than an empty vehicle in stopping from a specific speed.

Ultimately, this is a testing decision to be made by the vehicle testers, i.e., the MSP and LASD-LAPD. On one hand, it may make the vehicle testing more representative of how the vehicle is used. On the other hand, vehicles are tested without lightbars and spotlights to give the best results...under the knowledge that adding anything will lower the performance.

Representatives from both the MSP and LASD will discuss the ramifications of adding ballast to sedans and SUVs alike and report back to the LEPC. For their part, both testing agencies may do some preliminary tests during already scheduled SUV testing and provide both objective numbers and subjective EVOC instructor feedback.

Ultimately, however, regardless of how police agencies test the vehicles, GM tests them at a variety of conditions, including Gross Vehicle Weight Rating, GVWR. The word from GM Fleet is: Regardless of how much gear the 2007 Tahoe will actually hold, do not exceed the GVWR of 7,100 pounds for the 2WD and 7,300 pounds for the 4x4. The GVWR includes the weight of the vehicle, driver, passengers, optional equipment, upfitted equipment, 26 gallons of fuel and all cargo.

Published in Police Fleet Manager, Jul/Aug 2006

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