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Tech Tip: Hyundai Check Engine Light Diagnostics

January 19, 2010

As techs, we prefer to deal with the car with a driveability issue attached, as opposed to the light being the only problem, but both scenarios should be approached in the same manner.

Attach your scanner and make note of the codes that are ­recovered as you develop the diagnostic strategy for this job. But don’t be too quick to clear the codes; the next step is to review the freeze-frame data to see what was going on when the code was set. This information will be more helpful with certain codes, but it’s a good habit to get into no matter what the situation.

DRIVEABILITY ISSUES
First, we’ll look at some problems that have driveability complaints attached. The most common of these are misfire codes. If the misfire is obvious, you may be tempted to get to work and start switching coils, checking wires or whatever, looking to diagnose the problem. But before you do, check the codes and see if there isn’t more information available; if nothing else, the P0300 series of codes will identify the cylinder causing the problem.

But there are many other clues that may be available that will help in the diagnostic process. If you have a misfire code along with a system lean code, you should be thinking that the misfire could be a ­result of a manifold or other vacuum leak.

Even with no code, take a look at the data with an eye toward the fuel trim numbers: Do we have a high positive number on long-term trim, indicating that the system has been adding fuel? Or, is it the less common problem of a negative number that would have you looking at a rich condition, where an ­extreme case like an injector sticking open or a fuel pressure regulator leaking in the vacuum line could lead to the misfire? 

Another common driveability problem that may or may not have an associated code is a stumble or cutting out on throttle tip in. If the check engine light is lit, hook up your scanner and retrieve the code; the most common will be a system lean code (for more information on engine airflow sensors and engine management systems, click here). While you have the scanner installed, take a couple of minutes to look at the other available parameters. Are the temp sensors reading correctly with a cold engine? The coolant and air temps should be close. Taking a look at the throttle position switch, paying particular ­attention to the off idle area, there have been some ­reports of problems with the switches that become apparent when the connector is “wiggled.” Don’t overlook mechanical concerns; be sure to check the air intake hoses for cracks that will open up when the engine moves with torque.

In the case of “no start” problems, it pays to know the service history. If the car has suffered a broken timing belt, it’s a good possibility that some debris from the broken belt has found its way to the crank sensor, causing damage to both the sensor and trigger wheel. On the 2.4L engines, the balance shaft belts have been known to fail and go unnoticed until the pieces finally take out the crank sensor, resulting in a “poor run” or “no start.”

REAL-WORLD EXAMPLEELANTRA GLS
We recently had a 2002 Elantra GLS in the shop that had assorted problems. Let’s take a look at this job, as it’s a good example of some common problems you might encounter. The car wasn’t in great shape and a persistent check engine light was preventing it from passing state inspection.

As is often the case with this kind of job, the ­customer was reluctant to make a big investment, but wasn’t in the position to buy a new car. The obvious problem was a code for a solid misfire in the number 3 (P0303) cylinder, as well as a code for a slow ­response from the front O2 (P0133) and a system lean code. In addition, there was a slight but audible exhaust leak at the flex pipe before the cat. The customer had ­already installed a new O2 sensor, but the code persisted.
We explained to the customer that there was no way we could give a firm price on the job, but received authorization to get started with the diagnosis and get further authorizations as the job progressed.

The first step was to deal with the misfire. Since we also had the system lean code, we knew the problem was with cylinder 3; we went right to the manifold in that area. A quick shot of intake cleaner at the manifold flange smoothed the engine out, letting us know we were on the right track. To confirm and pinpoint the problem, we used a stethoscope where the sound of the leak was obvious.

Knowing that there was little cushion in this job, we checked compression as well as the ignition components to prevent being caught off guard when the gasket was replaced. When we were sure the miss would be repaired, and that the car would certainly run better with the manifold gasket, we got the authorization to replace the gasket and install a much needed set of spark plugs. With the gasket replaced and the engine running smoothly, we checked output of the rear O2 sensor, and it looked to be operating as expected in spite of the exhaust leak. With our budget constraints in mind, while we were aware of the fact that fresh air entering the exhaust system could lead to an O2 code, we set out to run the monitors in an attempt to get the car through state inspection, giving the customer some time to budget for the additional necessary repairs.

KEEP YOUR SCAN TOOL HANDY
Experience has taught us that the Hyundai line of cars can be a bit of a challenge when it comes to setting monitors, and it really pays off to be sure the setting criteria is met. We’ve gotten in the habit of having the scanner hooked up whenever we’re road-testing a driveability problem or setting monitors to confirm setting criteria.

In the case of the Elantra, we were looking for a starting coolant temp below 104 with a gain to 120 before the test would run. There are additional ­parameters that have to be met, depending on the monitor, and it’s well worth the time to look them up on your preferred service information system. The ECU knows nothing about close enough; if it’s looking for 104 degrees, 105 won’t do. The test will not be run. Some tests will look for a higher temp before the test is run. If the thermostat doesn’t let it get there, you’re wasting your time trying to run the test. I don’t know about you, but I can’t tell a 10-degree difference on the average temp gauge.

There are other advantages to driving with the scan tool. When I’m on the road, I like to keep an eye on the fuel trim numbers, as well as the calculated load. Fuel trim is the window into what the fuel control is doing; when you come right down to it, all it can do is add or remove fuel. If you’re seeing the short-term being adjusted, with the long-term chasing it and it’s staying near zero, you can’t ask for much more than that.

Calculated load tells us just what it says it does; it’s a window to the load the driver is applying. I ­always do a full throttle uphill pull and look for 100 percent load. If not, it’s a good bet that the mass air sensor is dirty, the intake hose is cracked or the throttle switch isn’t seeing wide open.

BACK TO THE ELANTRAOXYGEN SENSOR CODE
While the car ran well, it took only a couple of drives before we had the O2 code back. If you monitored the front O2 signal, it appeared to be switching well but was hard to tell if they were all within a second. Knowing that the exhaust leak could be an issue, we replaced the flex section of the pipe. With the now-quiet exhaust system, the signal from the O2 looked better and it took longer for the code to set, but set it did. At this point, we were back to our service info as well as checking for issues on iATN, something that should have been one of our first steps.

A quick search on iATN covered the things we ­already did, but it also mentioned problems with the grounding of the alternator bracket to the block, as well as the engine ground and body grounds near the battery. I’d like to say that I know exactly how the bad grounds ­affected the O2 readings, but I’m afraid I can’t. I can say, however, that after we cleaned the grounds the car set the monitors in two trips, and we had a successful repair and happy customer who no longer talks about needing a new car.

There are some other common failures with the Hyundai line of vehicles, but none are what could be considered pattern failures. We’ve had problems with coils and ignition wires that leak spark when damp after they see some miles, and engine coolant temp sensors that fail over time. There have also been some problems with wiring harnesses that can be tough to track down and should be kept in mind as you diagnose driveability issues. And these cars, while very reliable, aren’t immune to the same lack of maintenance problems that we see on other makes we service. Fairly common are things like mass air sensors ­becoming contaminated as a result of low-quality or dirty air filters, and cracked intake hoses that can ­result in stumbles and low-power complaints. And, don’t overlook the basics like the spark plugs.  

SERVICE INFORMATION
One thing is clearly apparent as we work to diagnose and repair driveability and emissions problems: The correct information to do the job is just as important as any scanner or scope. As with my example above, access to community forums like iATN can prove to be ­invaluable. In addition, Hyundai has made its service information website a free service, so there’s no reason not to register at www.hmaservice.com and take advantage of the information that’s available.  

Even more important is regularly making use of service information as part of your diagnostic strategy. Get in the habit of checking available information, whether it’s service tips like the ground problems that got us out of a tough situation with the Elantra, or knowing the criteria the ECU is looking for to set the code you’re chasing. Arming yourself with this information, and combining it with your personal experience and skills, will let you repair any car including the fine line of Hyundai vehicles in a professional and efficient manner.

 

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