By Dan Maslic

As we all know, warranty returns are not always the result of a defective product. Technicians often return product that works perfectly. Here are two high-tech returns your store might be able to avoid.

One of the more common problems faced by jobbers when dealing with electronic powertrain control modules is the relatively high number of defective returns, exchanges or warranty claims demanded by customers.

Yet, of all electronic parts that come back defective, ECMs tend to be the ones most often misdiagnosed. This doesn’t come as much of a surprise when one considers the level of complexity of modern ECMs, as well as the specialized equipment and level of expertise required to diagnose them.

Two ECM functions that are responsible for a disproportionately higher rate of ECM misdiagnosis are the vehicle theft deterrent system (VTD) and the computer-controlled charging system. When a new ECM is installed in a vehicle and the result is a no-start, plenty of technicians are quick to blame the new ECM when they know the old one started the vehicle. The same happens when an ECM is installed in a vehicle to cure a charging system problem, only to find out that the alternator still doesn’t provide a proper charge current. Reducing these unnecessary returns and warranties requires an understanding of how the VTD and alternator circuits work so that you can recognize when a misdiagnosis may have been made.

OE Theft-Deterrent Systems
A large percentage of vehicles manufactured over the last five years are equipped with OE anti-theft or engine immobilizer systems. VTD systems first became mainstream on some of the higher-end cars sold in the mid 1980s. Today, adding electronic content to a vehicle is relatively cheap, so it makes sense for OEs to add VTD systems to as many models as they can.

While each manufacturer has its own method for implementing VTD, many of the systems share one common feature, and that is to execute an engine immobilization function when the system detects an unauthorized start up of the vehicle. Engine immobilization is usually achieved through cutting fuel injection operation, or not allowing starter motor activation. When a new ECM is installed in a vehicle equipped with VTD, an anti-theft "relearn" procedure must be performed. Some manufacturers, like General Motors, provide a procedure that allows anyone to perform the anti-theft relearn procedure. In GM’s case, it’s an ignition key sequence that takes approximately 30 minutes to perform. The same can be accomplished with GM’s factory scan tool, the Tech II, in a fraction of the time. Other manufacturers, such as Ford, require that you use the factory scan tool only. No manual on-car procedure is available. The only exception to this rule is that of the J2534 programmer. If a J2534 programmer is used to extract the VTD key info, this can then be transferred to the replacement unit.

Chrysler, on the other hand, is somewhere in the middle. Most Chrysler products automatically learn the VTD info upon initial ignition key on following ECM replacement. These systems require no work on the technician’s part for relearn. Some Chrysler vehicles are equipped with Chrysler’s "SKIM" anti-theft systems which utilize a special transponder key to start the car. These systems require Chrysler’s factory scan tool to perform the VTD relearn function.

In any case, it is the technician’s responsibility to determine which type of VTD system (if any) a vehicle is equipped with and to take the appropriate repair actions. Just as your customer must know whether a vehicle has disc or drum brakes before ordering brake linings, he or she must also be aware of whether or not the vehicle is equipped with a VTD system. If a customer asks for an exchange, warranty or defective return on an ECM that isn’t allowing the vehicle to run, ask the customer why the vehicle doesn’t run. If the customer states that the fuel is cutting out, ask if the vehicle has good spark output. Most engine immobilizers cut fuel supply only. They do not typically cut spark. Therefore, if the customer tells you that the vehicle has no fuel but does have good spark, your customer may have overlooked the anti-theft relearn procedure. The same applies to a complaint of no starter motor operation. Reminding your customers of vehicle VTD systems may save everyone some time and money.

Computer-Controlled Alternators
Like VTD systems, computer-controlled alternators come in more than one flavor. GM and Ford use internal voltage regulators that may be commanded by the ECM, while Chrysler uses an external voltage regulator contained completely within the ECM. Generally, Ford vehicles are straightforward and few mix ups ever occur. GM, however, may use the same alternator housing for both computer-controlled and non-computer-controlled alternators on many of their vehicles with similar connectors.

This may present some problems for some mid-to-late 1990s models. During the mid to late ’90s, many GM models went to computer-controlled alternators. In the aftermarket, some alternator part numbers are listed that do not contain a regulator compatible with computer control. If the wrong alternator is installed in the vehicle (it may fit perfectly), the ECM or BCM may generate charging system trouble codes, and the alternator may not charge properly. If your customer experiences these problems, double check the part number and call your supplier for tech support if necessary to determine the proper part number for the application. The part supplier can verify whether or not the internal regulator of a certain part number is compatible with a computer-controlled system.

Chrysler vehicles, on the other hand, have been equipped with computer-controlled alternators for more than two decades, with the exception of only a few models. Chrysler ECMs contain an internal voltage regulator that varies alternator field current by varying the pulse width of the alternator field negative circuit. By applying a higher duty cycle to ground on the field negative terminal, the ECM can increase the alternator rate of charge. A lower duty cycle does the opposite, decreasing the alternator rate of charge. If your customer installs a new ECM and experiences the same symptoms as before, there may be other problems in the vehicle. An overcharging condition may be the result of a field negative wire being shorted to ground, or a short in the alternator field ground internally to the housing. A no-charge condition may be the result of a faulty connector, an open in the field positive or negative wires, or a blown fuse.

Understanding these systems can help give you an edge when dealing with technicians and installers that may want to return merchandise that is not actually defective. Asking some of the basic questions above may help keep unnecessary returns from coming back to your store. They may also help your customers get their vehicles back out on the road sooner and more cost effectively.

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