A fella recently took his car to a dealership for a bad transmission. Days earlier, he had a hard time getting it to move more than sixty miles per hour on the freeway. Screeching sounds yelled from the front of the car when he tried to accelerate, the needle on the tachometer spiked disproportionately with the rate of travel, and the engine was overheating. Sure seemed as though the transmission was slipping.
After inspection, the dealer called the fella and told him they could not get the vehicle to duplicate those symptoms. But apparently his alternator was putting out too much voltage and tripped a check engine light. Without installing a new alternator, they said, the mechanic would be unable to further diagnose any transmission problem.
New alternator installed, codes cleared, no further symptoms on test drive. Problem solved, right? Not exactly. The transmission still slips and screeches – just not for the mechanic.
Sound familiar? Intermittent issues – those that appear at random and are difficult to duplicate on command – are some of the most frustrating components of car ownership. They are frustrating for repair shops too. Intermittent car problems make it extremely hard to accurately diagnose trouble with a vehicle, even for an experienced professional with high-tech tools.
Why some car concerns are so complicated
If your brakes squeal every time you stop at an intersection, it is fairly clear that you are headed toward brake repair. If your check engine light comes on for a bad oxygen sensor, it might not be obvious to you what the problem is, but to a mechanic with a scan tool and the ability to apply the data it reads, it might be less ambiguous. Many car troubles are are not too tough to track down.
But some car problems are not so straightforward. Today’s automobile features complex and interconnected systems. Your traction control system, for example, is integrated with (among other things) the anti-lock brake system. When and how your transmission shifts is dependent on the position of the throttle in the intake on your engine. Even something as simple as a serpentine belt ties together several engine components; a problem with one of those components or the belt could cause other, intermittent faults.
Not to mention the advanced capabilities of newer vehicles: driver assistance, lane sensors used in autonomous situations, automatic braking and other crash avoidance measures, and adaptive cruise control that senses the car ahead of you. All of these are controlled by a network of computer modules and miles of wires.
A malfunction in one area can cause a problem in another. And problems do not always happen in a regular, patterned manner.
How intermittent issues are handled
Unfortunately, intermittent problems can take quite a bit of time to diagnose. Several frustrating visits to a repair shop are not uncommon. But they are sometimes necessary. Your mechanic must take on the role of a detective, observing and gathering evidence until a problem can be identified and case be closed.
What methods might a technician try?
Digging for DTCs. A Diagnostic Trouble Code (DTC) is an error message stored in your vehicle’s main computer (often called the Engine Control Module or Powertrain Control Module). When something goes wrong with a system component, sensors send data to the control module. The data is stored and the check engine light is usually turned on. Using an advanced diagnostic scan tool (not the kind you can put in your pocket for $19.99), a technician will “read” these clues and begin a search for the culprit.
Turning to TSBs. Vehicle manufacturers send out Technical Service Bulletins, or TSBs, to alert repair facilities when specific problems with a vehicle are identified. If hundreds of vehicle owners have the same concern, automakers will investigate and come up with a designated diagnostic procedure, repair plan, or replacement component. If the TSB is safety related, a recall might be issued. In any case, TSBs are an important resource when trying to diagnose an intermittent problem.
Testing the battery, starting, and charging system. Because so many systems on your car, truck, or SUV are computer controlled, any issues with the electrical system can cause a malfunction. An alternator that is putting out too much voltage, for instance, really can prevent the transmission from doing its job properly. A dead battery can cause data to be lost from computer memory too. And a car starter is a common intermittent issue.
Examining the wires and connectors. Loose, broken, or corroded wires or electrical connectors can cause intermittent problems. So can switches and relays. For instance, if your ABS warning light turns on and off randomly, one cause could be a bad wire leading to a wheel speed sensor.
Checking the cooling system. Let’s say that your car overheats occasionally. Seemingly for no reason. That, in itself, is an intermittent problem. It could be due to a bad thermostat, electric cooling fan, radiator, or fluid leaks. But an engine overheating can also cause intermittent issues to crop up in other areas.
Inspecting aftermarket accessories. An aftermarket accessory is any feature added to your car after it has left the factory. Aftermarket components may be included after you leave the dealership, or they may have been installed there. Upgraded audio and video systems, alarms, lighting, and remote starters, are all examples of aftermarket accessories. One downside to these “improvements” can be the electrical glitches caused by improper installation or incompatibility with other vehicle systems.
Investigating internet forums. In our interconnected world, it is not uncommon for a technician to take to the web in search of answers to an intermittent problem. The key, though, is to know what questions to ask. If you want a solid answer, you need to ask the right question.
Pinpointing the problem
Contrary to popular belief, a scan tool is not the answer to all of the ills in the automotive repair universe. Simply plugging in a code reader and cross referencing the readout with a repair is not how it is done. Sure, you can have the counterperson at your local auto parts store scan your vehicle in the parking lot. But that inexpensive scanner does not give all of the information necessary to locate a problem. Especially an intermittent one.
In reality, a diagnostic scan tool is just that: a tool. It takes a trained technician to not only interpret the results of a scan, but to pinpoint the problem from there. A scan tool simply tells the tech in which circuit a fault may reside. It is then up to the technician to conduct a subsequent series of pinpoint tests aimed at narrowing down the dilemma. This might be done with a digital multimeter or other devices. And here is where training and experience pay off.
How you can help
While it is essential to have a trained technician diagnose your intermittent problem, there are some things you can do to help. Consider the following list of signs to watch for and share with your mechanic when you have an intermittent car problem.
- What is the state of the weather when the problem occurs? Is it wet, cold, hot, humid?
- What is the engine temperature? Is the engine warmed up? Overheating? Still cold?
- At what speed is the engine running (RPMs) when the problem crops up?
- What speed is the car traveling? When driving slowly, or at highway speeds?
- Does it happen when you are accelerating or at a consistent speed?
- Do you notice the problem only when you hit a bump or drive on a rough road?
- Will it take place only when steering around a corner?
- Are the lights, air conditioner, heater, or some other accessory on?
- Does it happen only in stop and go traffic?
Intermittent car problems are certainly a frustrating case of “now you see it, now you don’t.” And they make take several trips to the repair shop before they can be fully resolved. Keep patient and leave it to a qualified mechanic at a trusted repair shop to get to the bottom of the mystery.
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