A Tutorial in Hyundai Driveability – UnderhoodService

A Tutorial in Hyundai Driveability

Diagnosing a driveability problem starts with the customer interview. When you are able to obtain the proper details about the vehicle’s symptoms, you will be able to diagnose the source of the problem more efficiently. Clues provided by the customer, such as “vehicle starts but runs rough until warm; worse when wet,” is invaluable information to get you started on your diagnostic routine and lead you to a successful repair.

After pulling in the car, open the hood, mist the secondary system with water or your preferred solution and, nine times out of 10, the problem becomes obvious and you know that it will be a successful repair. Such a scenario produces a good profit on the parts, it’s a nice labor job and the perfect opportunity to check the customer’s vehicle for related, necessary services and parts (such as spark plugs, filters and fluid changes).

Let’s take a look at some of the problems you are likely to see when faced with diagnosing a driveability complaint on a Hyundai. Like any other vehicle, most driveability problems will be traced to basic systems. Even if you’re armed with good information, it’s important to road-test the car and duplicate the complaint before attempting any repairs. This is also the time to make note of any other problems you may have noticed that the customer failed to mention. Don’t overlook the little items, such as lubricating a squeaky door or tightening the armrest. Customers expect us to fix their cars, but it’s the little extras that will make your shop special.

If you’re lucky, you’ll get the car in and the problem will be obvious. Maybe it’s a dead miss or an idle problem. Unless the customer complaint includes a cold idle problem, I recommend taking the time to test-drive the car. I know that if I can duplicate the problem, I can be sure the repair was successful during the final road test. And even if your customer has provided details about the problem, it’s never a good idea to assume anything. I’m sure that I’m not the only one who has wasted time looking at a no-power complaint, only to find out the clutch was slipping once I finally road-tested the car.

When There’s No or Low Power
Hyundai has had its share of no-power complaints. Most of these complaints are on older models with high mileage. Oftentimes, these problems will lead to a plugged catalytic converter. It’s not unusual that the first symptom the customer gets with a plugged converter is a no-start problem. Diagnosing this problem on a Hyundai can be a little trickier than on other nameplates. Normally, you would expect a plugged exhaust to always be plugged. Sure, they will get worse as they heat up, but the problem is usually easy to pick up on a road test. But the converter on a Hyundai will fail and the catalyst will break up into pieces, caused by the effect of heat and the exhaust gases, and will fill the outlet of the converter shell and block the exhaust almost completely.

The first one we saw was a diagnostic challenge. If you suspect a problem with the catalytic converter, don’t forget that it’s right under the exhaust manifold. Remove the O2 sensor to access pre-converter exhaust gases to either test the pressure or provide a path for the gases. If you get one of these cars in and detect that it has wet spark plugs with good spark, yet it won’t fire even after the cylinders have been dried out and the new plugs have been installed, the next thing I would check is the exhaust.

Be sure to also check the motor oil, since it likely needs to be changed. It may have to be done as part of the drying-out process. Depending on how long the customer tried to start the car, the crankcase may have quarts of gas mixed in with the oil. Even if the crankcase isn’t overfilled, always recommend the oil change.

Other low-power complaints may be traced to misadjusted timing belts and/or tensioners. Without getting into timing belt replacement, it’s important to note that some techs are not properly adjusting the belts. They improperly preload the tensioner, and the resulting loose belts are jumping and upsetting the cam timing.

Don’t forget to tee in your vacuum gauge to get an idea of what the intake manifold is seeing. One simple hook up will let you know if the engine is passing air.

Any problems with exhaust flow or valve timing will certainly be evident. If you aren’t using a vacuum gauge as part of your driveability routine, you should give it a try. As with any tool, once you know what you’re looking for, the problems are easy to pick up. As a rule, three or four inches of vacuum are what you’re looking for when cranking with a strong battery and closed throttle.

If the car runs, you’ll be looking for something in the high teens or low 20s at idle. Open the throttle, and vacuum will drop and then recover as air passes through the intake. No vacuum cranking could either point to the valve timing or a plugged cat. On Hyundais, I would remove the O2 sensor and retest. Low vacuum at idle, combined with a low-power complaint, would have me thinking that valve timing was the problem or, depending on the model, base ignition timing. If there is a slow recovery of vacuum after opening the throttle, I’d be looking for a restricted exhaust that won’t let air pass through the engine.

Getting the DTCs
Now back to the road test. Say that you’ve driven the car and can’t duplicate the problem. The next step is to access the on-board diagnostic system. Hyundai has made it easy for us get codes, although it is a little different than what we may be used to doing. Using an analog voltmeter connected to the data link connector in the fuse box, we can count the sweeps and length of time on the meter to give us long and short sweeps. The long sweeps are 10s and the short sweeps are ones. Two long sweeps, followed by one short sweep, is a code 21. On a 1992 Excel, for example, that would be the coolant temperature sensor.

Note: When you’re working on a Hyundai, it is extremely important to remember that fault codes are circuit specific, rather than component specific. In this case, the code is a good indication that the ECU is not seeing information from the coolant temperature sensor that it expects to see. It’s not indicating that the sensor is at fault.

On the later model cars equipped with OBD II, you’ll need a scanner to access codes, as well as a strong data stream that will make the diagnostic process easier and faster. But like the earlier cars, don’t be too quick to replace components. I hope that your shop has made the wise investment in a scan tool with Asian software, which can be a big help with the diagnostic process on Hyundais. In addition to retrieving codes, you’ll find the data stream to be thorough and quick, allowing you to look at what the computer is seeing.

By hooking up the scanner on this car that we’ve been road testing, we can retrieve any codes that may have been stored within a couple of minutes. If a code is set, it could be a big help in pinpointing the problem as long as it’s related to the complaint. If the code has nothing to do with the symptom, make a note of it but don’t let it send you down the wrong path. There is no point in checking the mass air flow sensor on a car that runs well because a code has been set. It could have been set when the air filter was checked and the sensor was left unplugged while the car was started. Write down the codes and clear them. On the earlier cars, if you’re not using a scanner, you’ll have to disconnect the negative battery cable to clear the codes.

The Inevitable Pattern Failure
Since changing over to fuel injection, Hyundai has earned a good reputation for driveability and its vehicles don’t have many pattern failures. The most common and frustrating failure was covered in a 2002 Mitchell 1 technical service bulletin. It covered a poor splice in the negative side of the sensor circuit. Because this circuit has an effect on all the sensors, this problem will cause many different complaints. Since the problem is at the splice, it may affect the coolant temperature sensor one time and set that code. The next time it runs bad, it may be the air flow meter ground that goes open and sets that code.

If you’re working on a car that seems to have a lot of codes and intermittent problems, think about the ground side of the sensors. On some cars, only one leg of the splice is bad and it affects just one of the sensor circuits.

We once worked on an Excel that would start and stall once in a while. The MIL lamp would come and go, but would always set a coolant temperature sensor code. Finally, the connection got bad enough that we were able to see the problem. With a voltmeter hooked to the positive side of the sensor while driving, we would see the full reference voltage. Since the sensor resistance was correct and the connection was good, we simply added an extra ground for the temperature sensor and that took care of the problem.

Most of the time, the bad ECU will result in a no-start complaint. But some of them will present other symptoms. Of course, you wouldn’t declare a computer bad without confirming the power and ground circuits to the unit. After calling the dealer to check on the price of the ECU, you will be looking for another source.

Depending on the year and mileage of the car, using a used unit or sending the unit out to be rebuilt are both good options we’ve used with success.

When we checked the codes on the car we’ve been road-testing (that has no symptoms), there were no codes present. Before you return the car to the customer, asking him or her to drive it until the symptoms are more evident, double-check the ignition secondary system and don’t forget to look at the spark plugs.

We know that Hyundais appeal to commuters and young people, who may not be the kind of drivers who keep a close eye on the maintenance schedule. I’m not a fan of selling a “tune up” in an attempt to repair a driveability problem. But if you remove a spark plug and the center electrode is eroded down to the insulator, the car is telling you it needs to be serviced. There is no point in looking for driveability problems until this service is performed.

While the service is being done, be sure to recall the original complaint. It is more efficient to replace the bad wires, cap and rotor while doing the service, than it is to have the customer return after spending a couple hundred dollars, only to still have the same symptoms. Don’t sell them stuff they don’t need, but don’t overlook needed items.

Other problems you may find on Hyundais are no different than the things you’ll see on other nameplates that share the same systems. Hyundai has used both mechanical and hot-wire air flow sensors. The door on the mechanical unit, which can cause problems with binding and sticking, should be no problem to diagnose. Simply operate the door while you’re replacing the air filter to check for nice smooth operation. The hot-wire sensor has proven to be a reliable piece with few problems.

By far, the most common problem you’ll see with the air intake system is the hose that connects the intake manifold to the air sensor. Cracked intake hoses are a common problem with many brands, but they continue to be overlooked by some techs. This problem will result in a big hesitation when the vehicle is accelerated hard from a slow speed or standing start. When the engine strains against the motor mounts, the crack in the hose opens, allowing unmeasured air into the engine. The resulting lean mixture makes the engine stumble, closing the opening and starting the whole procedure all over again. If you are working on a vehicle that stumbles upon acceleration, give this hose a good inspection. They usually crack on the bottom, so it may be necessary to pull it off the air filter box and bend it to find the crack.

Well, these service and diagnostic procedures fixed the Hyundai we road-tested. As mentioned earlier, most of the driveability problems can be traced back to basic systems, and the system that seems most suspect is the ignition secondary. Hyundai, like all the other car makers, is eliminating most, if not all, of the secondary system by changing over to DIS or coil-on-plug systems. There have been some reports of problems with these new systems, but they are few and far between right now.

You should welcome Hyundais into your shop, as they will provide you with good repair opportunities and not many repair dilemmas. Which may just be what you’re looking for!

Did You Know… Hyundais also have more problems with ECUs than we are used to seeing on other vehicles. I’ve heard that many of the problems are the result of low-quality rebuilt alternators and the resulting overcharging that takes place. I’m sure that some of these problems are also the result of careless jump-starting. Whatever the reason, keep it in mind that they fail.

What’s Hot and Not Among Car Thieves

The 2002-’03 model Cadillac Escalade EXT and the 2002-0’3 model Nissan Maxima have the highest theft claim rates among newer passenger vehicles – seven to eight times the average for all cars. These are the latest insurance theft loss results for passenger vehicles one to three years old published by the Highway Loss Data Institute (HLDI), an affiliate of the Insurance Institute for Highway Safety.

This is the second year in a row that an Escalade is among the vehicles most likely to have a theft claim. The Escalade’s theft losses are the highest even though this vehicle is equipped with a standard antitheft ignition immobilizer. An immobilizer is built into a vehicle’s electronic ignition system and is supposed to prevent the vehicle from being started without the proper key.

One reason the Escalade is a top target is that some are equipped with expensive accessories like custom wheels. Stolen Escalades are sometimes found resting on blocks without their wheels and some custom chrome wheel and tire packages can cost more than $10,000.

The Maxima’s theft claim frequency increased dramatically after Nissan began equipping this car with expensive high-intensity discharge headlights as standard equipment in 2002. While the Maxima’s theft claim rate was eight times higher in 2003, compared with 2001, the average cost of each claim went down. This indicates that, in many cases, the stolen cars were recovered with damage or that items such as the headlights were stolen from parked cars. Source: Insurance Institute for Highway Safety


Hot Cars

Highest theft claim frequencies, 2001-’03 model passenger vehicles




Claim Frequency

Cadillac Escalade EXT (2002-’03)


Nissan Maxima (2002-’03


Cadillac Escalade (2002-’03)


Dodge Stratus/Chrysler Sebring


Dodge Intrepid




Cold Picks

Lowest theft claim frequencies, 2001-’03 model passenger vehicles




Claim Frequency

Buick LeSabre


Buick Park Avenue


Ford Taurus (station wagon)


Buick Rendezvous 4WD (2002-03)


Saturn LW (station wagon)


Average all cars


Note: Claim frequencies are per 1,000 insured vehicle years.


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