Mechanical Repair In The Collision Shop

by David Berlien

Differences between a collision shop and mechanical shop continue to blur with each passing year. The complexity of today's automobile, with its myriad of electronic systems such as anti-lock brakes with traction control, frontal and side airbags, heads-up displays, truck-mounted cellular phones and compact disc changers, means that the collision shop estimator, insurance adjuster and collision technician must be knowledgeable about mechanical systems and their repair requirements.

Many collision shops employ full-time mechanical technicians to eliminate the need to sublet collision-related mechanical repairs. A well-trained mechanical technician can eliminate collision technician mistakes and problems.

Even simple things such as disconnecting a battery can create problems. For decades, technicians have been taught to disconnect the negative battery terminal first. This method interrupts the electrical current at its source and minimizes voltage spikes that can damage sensitive electronics. Some Japanese vehicles equipped with airbag systems, however, have an energy reserve capacitor that requires the disconnection procedure to be reversed. On some Mitsubishi and Mazda vehicles, the technician must disconnect the positive cable first and touch it to the still-attached negative cable. This discharges the airbag capacitors that store energy for deployment. Using the standard "negative first" battery disconnect procedure on some Asian vehicles could lead to stored diagnostic trouble codes or accidental deployment. An accidental airbag deployment is expensive and could result in technician injury or worse. This example of "old rules of thumb" no longer applying demonstrates the need for mechanical education in the collision shop.

Wiring Harness Repairs
One often improperly performed mechanical service in the collision shop is wiring harness repair. Once again, for decades, collision technicians and estimators understood the basic, simple rules for wire harness repair. In short, technicians either soldered the wires and covered the joint with electrical tape or installed standard butt connectors and covered the butt connectors with electrical tape. Today's wiring harness repairs must take into account multiplexing, sensitive electronic sensors and a liability climate that makes proper repairs more than just a customer satisfaction concern.

Before writing an accurate damage report, estimators must know what repair restrictions exist and what method of repair is recommended for a particular vehicle. Before undertaking wiring repairs, technicians should be trained and have access to vehicle-specific repair information to ensure that all repairs are done in the proper manner.

In an effort to reduce cost, complexity and weight of wiring harnesses, single wires can operate multiple systems. Something as simple as the added resistance of a corroded butt connector can cause a multiplexed system to turn on the windshield wipers instead of the cruise control. For example, a multifunction switch sends 4.2 volts or 2.6 volts to a control module over a single wire, depending on what position the switch is in. The control module recognizes the 4.2 volt signal as a command to turn on the cruise control and recognizes 2.6 volts to turn on the windshield wipers.

If a corroded wire splice or excessive splice resistance reduces the voltage when the switch is in the 4.2 volt position, the control module will not turn on the cruise control and may turn on the wipers instead. For this reason and others, each automaker has developed specific repair and replace information.

Examples of this type of automaker-specific information include the following:

General Motors

Ford Motor Company

Chrysler

Wiring harness repair procedures, requirements and limitations differ from automaker to automaker. The potential liability problems that can arise from failing to follow OEM recommendations, especially on life-and-death systems such as anti-lock brakes and airbags, should motivate the estimator and repairer to seek model-specific information regarding wiring repairs.

Air Conditioning Service
Many collision shops today have already purchased recovery/recycling stations for automotive A/C service. Air conditioner service used to be exclusive to the service department or independent auto service center, but is now commonly performed in the collision shop. The introduction of CFC-free refrigerants, primarily R-134a, has required further mechanical training and service equipment for the collision shop.

For many years, mineral-based refrigerant oils were used in automotive applications, with Harrison oil being a commonly used product. Today, the technician needs to be aware that R-134a systems do not use mineral-oil based lubricants. One exception is the compressor oil specified for the '96 Dodge Avenger and Chrysler Sebring equipped with double overhead cam engines. These vehicles use 3.4 fluid ounces of ND-OIL 8 lubricant instead of the 5.7 ounces of PAG-56 that the single overhead cam engine requires.

The Environmental Protection Agency (EPA) has recently approved new materials for refrigerant use. R-40c and FRIGC FR 12 are two examples, but it appears that automakers have decided they have already spent enough money converting to R-134a and expect no change in the foreseeable future. Technicians will need to be more careful when evacuating charged systems because there is a greater chance that unapproved refrigerants will find their way into collision damaged vehicles. With existing R-12 supplies dwindling and prices skyrocketing, the incentive for unscrupulous repairers to use propane- or butane-based refrigerants will increase. The technician may be well advised to use a refrigerant tester to ensure that the recovery or recycling station is not contaminated with this very flammable type of refrigerant.

Cab-forward Design
Although you will not hear the phrase "cab-forward design" from any automaker except Chrysler, all new automobile designs share the basic concepts. Passenger compartments are a larger percentage of overall vehicle length. Wheels, tires and suspensions have been pushed farther from the center of the vehicle to allow more front and rear leg room. Cab-forward design shortens the length of the engine bay and forces the hood line lower for the aerodynamic design. As a result, mechanical accessories have been packed into a smaller space. Collision shops should expect to have more damaged mechanical components than ever before in comparable hits because of the tightly packed engine compartment. Good examples are the Chrysler JA sedans (Cirrus, Stratus and Breeze). These vehicles have very short engine bays as a percentage of vehicle length. It only takes a minor collision to push the core support back into mechanical accessories such as the control modules, exhaust system, O2 sensors and A/C components. As more space is added for people and cargo, collision shops will have to deal with more mechanical system damage.

Future Trends
This year, there will be a new crop of side airbag systems from automakers. How each of these airbag systems will work and how they will be serviced remains to be seen.

Cadillac is introducing their anti-skid system as part of the Northstar system. The system has a vehicle yaw sensor located under the package shelf that communicates vehicle response information to the steering inputs. If the control module processes signals that indicate the vehicle is sliding sideways or failing to turn as quickly as the steering wheel angle indicates, a signal is sent to the anti-lock brake modulator and the brakes are applied selectively to the wheel that will correct the yaw problem. It will be interesting to see what happens to the yaw sensor when a new Cadillac gets hit in the rear quarter and the lock pillar and the yaw sensor experiences six or seven Gs. Will it still work? Will we need to read the codes with an OBD II-compatible scan tool?

How common will heads up displays become? Will the infrared night vision heads-up displays, common in police cars, become available to the general public? Will the advantage of seeing further in the dark, through fog, rain and snow, mean more mechanical repairs for the collision shop? Will on-board satellite navigation systems be as common as cellular phones? What about intelligent highway interactive systems?

This article only scratches the surface of the future of mechanical repairs in the collision shop. One conclusion seems obvious: differences between the mechanical shop and collision shop will continue to blur.

David Berlien has been an Inter-Industry Conference for Automotive Repair (I-CAR) instructor since 1988 and is a long-time member of ASA. He and his wife, Karen, founded Automotive Technical Education Group (ATEG) in 1990, which develops collision repair training programs that focus on new models.

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AutoInc. Magazine ®, Vol. XLIV No. 12, December 1996