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Electronics: Where I Buy

By Gary Goms

Choosing an electronic part isn't easy for the quality-conscious technician.

Although a few veteran mechanics still remember when the “transistorized AM/FM radio was the only solid-state, electronic component to be found in vehicles of the 1960s and 1970s, today’s technician is confronted with a multitude of solid-state, electronically driven computers, modules, sensors and actuators that control or monitor virtually every aspect of modern vehicle operation.

Because performance and reliability are the essential characteristics of any electronic component, choosing a replacement can be much more demanding than simply selecting a favorite brand or buying the cheapest part. Top-drawer technicians know from experience that, on the average, buying the cheapest part results in the greatest loss of time simply because the cheapest part brings with it a host of quality control and reliability issues.

The proliferation of multiplexed electrical systems is causing the average electronic content to increase dramatically in modern motor vehicles. To illustrate how this happens, a minimum of four modules, let’s say the engine, antilock braking, air bag, and transmission computers, might share a common sensor input, such as the input from the vehicle speed sensor (VSS). The fact that one sensor can provide data to multiple on-board computers has allowed engineers to electronically control or monitor most mechanical vehicle functions. Of course, this networking capability requires that any electronic part purchase must not only serve the conventional definitions of form, fit, and function, but be compatible with other on-board electronics as well.


At first glance, buying a quality electronic part might seem like a simple process. But, believe me, choosing an electronic part isn’t always easy for the quality-conscious technician because the only way to find the quality part is through the experimenting with various brands. To illustrate, all computer-controlled engines depend upon five primary sensor inputs such as intake air temperature (IAT), engine coolant temperature (ECT), throttle position (TP), manifold vacuum and barometric pressure (MAP), mass air flow (MAF) and exhaust oxygen content (O2 sensor).

A small calibration error in any of these sensors can seriously affect fuel economy and engine performance without storing a diagnostic trouble code or illuminating the check engine light. The only way a master technician can determine the quality and reliability of the part is to install it, measure its performance, and keep records of its overall reliability.

Quality issues are even more prevalent with remanufactured electronic parts like engine OBD I control modules (ECMs) or OBD II powertrain control modules. These modules can create tough diagnostic problems for a technician because they might contain a heat or vibration-sensitive failure that was undetected by the remanufacturer during the rebuilding process.

Last winter, for example, I spent days trying to duplicate a rough idle and stalling condition on a 1988 GMC pickup. Because the condition occurred only during cold weather, I had made the assumption that cold weather was affecting an actuator like a fuel injector or an input device like the magnetic pickup in the distributor. Since this vintage of General Motors vehicle has a history of cracked magnetic pickups in the distributor, I replaced the distributor as a precautionary measure.

The long story short, I eventually discovered that turning on the passenger compartment heater would initiate the rough idle and stalling complaint after about two hours of running time. After discovering the failure pattern, I spent another two hours determining that the newly remanufactured ECM was actually causing the stalling condition by holding the fuel injector open and momentarily flooding the engine.

Since the ECM was located just above the heater assembly, the injector driver in the ECM would overheat only when the heater was turned on in the winter. To make matters worse, the replacement ECM produced a similar symptom after an identical two hours of running time. I eventually discovered that the replacement ECM was defaulting into a “limp” mode when its core temperature reached 150 degrees F, again after the passenger compartment heater had been turned on. The limp mode, which is designed to return the ECM to base spark timing and fuel control parameters when the ECM itself fails, nearly duplicated the physical symptoms of the original failure, which were a rolling idle speed and rich fuel operation. Needless to say, the value of extensive diagnostic and testing time far exceeded the value of the two remanufactured ECMs.


Unlike a serpentine belt shredding or an alternator failing to charge, most electronic components usually develop an intermittent failure that requires at least three to four hours of diagnostic time to determine a failure pattern, replace the component and verify the repair.

Intermittent electronic component failures are usually caused by an open or shorted circuit in a microscopic circuit board that’s permanently sealed in a plastic box. This situation, which renders the failure invisible to the human eye, requires a deductive diagnostic strategy that measures and compares electrical inputs and the resultant electrical outputs from the allegedly defective “black box.”

In some cases, the part is diagnosed by ruling out all other possibilities. In other cases, the part is diagnosed by the technician using his experience, equipment, and his intuitive ability to understand intermittent systems failures.

When discussing warranty repairs, let’s keep in mind that average labor rates for what the industry terms a “tier one” or top-level shop are currently hovering between $80 and $100 per hour. In some high-income areas, labor rates are as much as $140 per hour. When we balance current labor costs against parts costs, labor represents at least 60 percent of the average repair invoice.

So, when we balance a $20 savings in parts cost against the possibility of losing $200 in labor costs spent diagnosing an intermittently defective electronic replacement part, the math simply doesn’t work in favor of buying the cheaper part.


When I choose an electronic part, I always balance the probability of a warranty failure against the price of the part. In some cases, aftermarket and OE might source a particular part from the same vendor. In these cases, I usually choose the aftermarket supplier because I know that if a warranty situation presents itself, I will usually face less difficulty having the part replaced.

This is the case with using the aftermarket remanufactured ECMs. I don’t think the failure rate significantly differs between the OE and aftermarket ECM, so I always choose the aftermarket ECM whenever possible. All too often, many dealership parts departments adopt the philosophy that their parts “never” fail. Unfortunately, any technician who has done new-vehicle warranty work for a dealership knows otherwise because new vehicles with new parts fail quite frequently on a warranty basis.

On the other hand, if a part is difficult to replace or if precise calibration is an overriding concern, the overall performance and reliability of the OE part might make an OE part the better choice. Under these demanding conditions, I would probably choose the OE part over an aftermarket part of undetermined origin and quality.

At this point, we must also address the increasing influx of replacement parts being imported from China and other overseas sources.

All too often, quality control is an issue that can literally be lost in the “translation” from domestic blueprint to off-shore production line. Too many finished parts simply don’t pass the form, fit and function criteria because they might be dimensionally incorrect, difficult to install, or don’t perform to specification or perform as reliably as the original.

The concern about the quality and reliability of imported electronic parts is high among independent shops because an increasing number of aftermarket and OE suppliers are sourcing from Asian and other overseas manufacturers.

Because electronic components are becoming more prolific and because undertaking warranty repairs on poorly performing and unreliable electronic parts quickly erode a shop’s bottom line, it’s not unreasonable to expect independent shops to adopt an even more demanding attitude toward quality and reliability in the future.

  Previous Comments
avatar   Dan   star   12/30/2009   7:44 PM

Matt, when was the last time you bought a MAP sensor or TPS at Best Buy or a yard sale? If you don't understand the joke, don't blame the comedian. How much money did you waste on extra parts before you found the ones that fixed it. Or do you work at the "try it before you buy it" store? And, I do it (idoit) but I'm not an IDIOT. I can spell.

avatar   MATT   star   12/27/2009   5:55 PM

I RECENTLY BOUGHT AN 88 f150 4x4 and spent 2 weeks trying to fix it finally got it throttle position and map both bad same time no scan tools used dan is an idoit

avatar   Dan   star   12/13/2009   11:55 AM

I usually buy my electronics at yard sales or maybe Best Buy

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