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Mazda Feature: Driveability And Check Engine Light Diagnostics

Import Specialist Bob Dowie takes a look at some of the more common ailments that will bring your Mazda customers into your service bay with a check engine light complaint, as he covers common DTCs, stalling and ignition issues and new technology.

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This article will look at Mazda driveability issues as well as some of the more common ailments that will bring a car into your bay with a check engine lamp complaint. The most common failure we see on Mazda models is a torn air intake hose between the airflow sensor and the throttle body. The symptoms that result from this failure are hard to miss, but fool the customer into mistakenly thinking that the transmission is the problem.

The usual complaint is a big stumble or stall on initial ­acceleration. As the engine torques on the mounts, the crack in the hose will open, allowing unmetered air into the manifold, while, at the same time, reducing airflow through the mass air flow sensor. Of course, when the engine stumbles, the crack closes, allowing the engine to accelerate, starting the entire process all over again.

Although it’s simple to diagnose with a ­visual inspection, I’ve seen some good technicians tricked by this one. These hoses become hard and brittle over time, and you may not find the fault simply by squeezing the hose. Be sure to inspect the hoses closely for cracks that won’t be obvious but will become evident when the engine is loaded against the mounts.

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Another issue is a P0400 code, excessive EGR flow. The first problem is the fact that an “excessive flow” code will be thrown, when the actual problem is “insufficient flow.” The excessive ­report is the result of the ECU commanding more EGR when the engine doesn’t respond as expected to the EGR valve being opened. The most common cause for this lack of response is plugged EGR passages in the manifold. By ­removing the throttle body and EGR valve, the passages can be cleaned using a ­liberal amount of carbon cleaner and a piece of speedometer or hand brake cable and a drill.

On some models, it will be necessary to remove the upper plenum. Be sure the vacuum line and manifold nipple are clear going into the MAP-type sensor that serves as the EGR boost sensor. Don’t let the term boost sensor confuse you; it’s a manifold pressure sensor that’s used to monitor the pressure change when the EGR is commanded open.

On the later models that use an electrically ­controlled EGR, there have been instances where the valve has caused issues with a throttle tip-in stumble, stalling or rough idle. These complaints may be accompanied by a system lean code. If the rough idle is caused by a partially open EGR valve it’s easy to ­diagnose: Just let the engine warm up and look for flow through the valve by checking to see if the valve is excessively warm. We know there shouldn’t be any flow through the valve at idle; if so, the high temp ­indicates that the spring-loaded valve is not seating. 

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STALLING ISSUE
A stalling issue can be a bit more challenging, since it could be an intermittent problem with the valve not closing. In this case, we check other possibilities for stalling; if we find no problems there, we go with our experience and replace the valve. The same scenario applies with a throttle tip-in stumble. In this case, the weak return spring in the valve is ­allowing more flow than the ECU is commanding. If you suspect this problem, a road-test with the valve disconnected will quickly confirm it.

While a sticking EGR can cause a system lean code, it’s not the most common cause. The first step when faced with a lean code is to be sure to look at the freeze-frame data. Look at the fuel trims and the conditions when the code was set. You’ll probably find a long-term trim number near 25. This is the ­result of the short-term trim adding fuel and driving up the long-term number. If you’re looking at a multi-bank engine, take note if both banks are showing a similar number or if it’s just one bank.

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Freeze frame will also tell you when the limit was reached. Armed with this information, you can make some decisions. If the limit was reached at idle, it would have you looking for unmetered air finding its way into the engine. It could be the EGR valve, but could also be an intake manifold gasket leak, or the O-ring seals on the V6.

On the four-cylinder, a leaking intake gasket will usually set a misfire code, along with the system lean code, letting you know where to concentrate your inspection. Usually all it takes is a shot of intake cleaner at the manifold flange and stethoscope to confirm the diagnosis. The six-cylinder’s upper manifold O-ring leaks can be a bit more challenging, and if you’re in doubt, a smoke test will confirm you’re on the right track.

On the other hand, if the freeze-frame information is telling you that the code was set at speed, the idle is smooth and the driver reports no additional symptoms, you would have to think about what makes it lean under those conditions. My first thought would be the mass air flow sensor is not reporting all the air flow to the ECU; by now we should all be aware of how debris finds its way to the hot wire sensor.

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If you’re going on an initial road-test after checking and clearing the codes and memory, set the scanner up to monitor the fuel trims, front O2 and calculated load. Before you hit the road, make sure the O2 and short-term trim is switching as expected. On the road, do a couple of wide-open accelerations, making note of the ­calculated load; it should a 90-plus percentage. If not, take a close look at the mass air flow sensor for contamination.

The sensors can be carefully cleaned — and we’re having good luck with some of the products designed for the job — but be gentle as they are fragile. We look at cleaning the sensor as part of the diagnostic process and recommend a new sensor to ensure a successful repair, so be sure to note that on the invoice to prevent any misunderstanding.

Once the problem is diagnosed and repaired, make sure that the bolts holding the sensor to the air filter housing are tight, that the air filter box is not allowing unfiltered air into the sensor, and that the air filter element is of high quality and in good condition. There have also been reports of the sensor housing bolts coming loose, letting dirt into the air stream, so be sure all the air is being filtered.

IGNITION SYSTEM
A P0300 series code indicating misfires has us moving to the ­ignition system. Many times, a misfire code will have a driveability complaint associated with it, but either way the diagnostic strategy is similar. If the miss is always evident, it shouldn’t take you long to figure it out. Be sure the engine is mechanically sound with good ­compression and spark plugs that are in good ­condition.

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While you’re there, take a good look at the wires for any cracking or indication of carbon tracking; look closely for pinholes burnt through the plug boots that would let the spark get to ground. If any oil is evident, replace the valve cover gasket with spark plug tube seals. If the oil is deep enough, that could very well be the cause of your problem. Grab your stethoscope and be sure the injectors are opening and closing by listening for that distinctive click with the tool in the same ­location on each injector; they should all sound the same.

With Mazda’s distributorless ignition (DIS), using waste spark, coil pack and coil-on-plug systems, as the miles add up, none of the systems have been immune to problems. Plug wires have been the most common failures, but we’ve seen some coils fail as well. In the best case, the OBD II system is reporting the offending cylinder, sending you in the right direction. If not, it can be tough to pinpoint the ­offending cylinder, especially if it’s an intermittent problem.

While you can use a low-amp probe to look at the coils, it can be difficult to catch the problem. On a higher mileage, four-cylinder car that uses two coils and two wires, I would tend to replace all the components. On coil-pack cars, history tells us wires are the more common failure.

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With six-cylinder, coil-on-plug cars where the cylinder can’t be pinpointed, you have to decide if you should change them all or wait for the failure to become more evident. That decision would require a discussion ­between you and your customer. On the models that require manifold removal for access, we ­always recommend replacing all the coils and plugs while we’re there.

The other weak link in the ignition system is the distributor itself. You may have a complaint that the car cut out, but when it was started back up, it seemed fine. Or maybe it just cut out and wouldn’t start. There are no serviceable parts in the Mazda ­distributor, so if you have a no-spark condition that is traced to one of the components housed in the distributor, the unit will have to be replaced.

Actually, on some models, the ­igniter is available, but it costs as much as a rebuilt distributor. The aftermarket offers high-quality rebuilt units, but they don’t all come with the O-ring. You may be able to carefully ­replace the old one, but it’s much safer to have a new one on hand. When the time comes to put on the timing light, be sure to check your service information for any special procedure required to set the base timing.

If you ignore a misfire code for any length of time, you will be faced with a P0420 catalytic converter efficiency code. Again, using the data side of the scanner, we want to take a look at the front and rear O2 sensors to see if the “cat” is doing its job. Unfortunately for the customer, we usually see the sensors mirroring each other, telling us the misfire has damaged the converter. If the front sensor were switching nicely while the rear remained steady, we’d know the cat’s doing its job. Keep in mind that the cats are covered with an eight-year, 80,000-mile ­warranty.

LATEST TECHNOLOGY
While Mazda has long enjoyed a reputation for high-performance, ­affordable cars, the engineers haven’t stopped looking for ­improvements. The latest is its SKYACTIV technology. Its SKYACTIV-D engine, for example, touts the world’s lowest diesel-­engine compression ratio: 14.0:1, ­producing 20% better fuel efficiency. Mazda accomplishes this using a sequential twin turbocharger ­induction system setup to cram more air into the cylinders when the engine is running. There is a smaller turbo and a larger turbo that can work together or independently. The smaller turbo helps reduce turbo lag at low rpm, while the larger turbo supplies increased boost pressure for high-speed power.

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Mazda engineers also worked hard to reduce parasitic drag in the engine, as well as the transmission, resulting in better fuel mileage and increased performance. Go to www.mazda.com and click on the SKYACTIV tab for more details. 

 

Late-Model Mazda Issues 

There have been some reports of wiring harness failure in the popular Tribute model that could shut down an injector or coil on acceleration and set the appropriate misfire code. The failure is usually within a couple of inches of the ECU; a shake and wiggle test will confirm the problem. But with the wire breaking inside the insulation, it would be time well spent to check a pin chart to better identify the suspected wires.

The problem with system lean codes hasn’t gotten any better, but the possible causes have changed. There are still problems with contaminated mass air flow sensors, and intake hoses that can be diagnosed as previously discussed. 

We’re seeing some new problems that will lead to lean codes at idle. Like the sticking EGR valves on the earlier cars, the purge valves are not closing causing vacuum leaks most prevalent at idle. You’ll see a high reading on long-term fuel trim as the ECU tries to add enough fuel to compensate. It’s an easy problem to confirm; with the engine running there should be no vacuum on the vent line side of the valve. Like the EGR valves, this can be an intermittent problem. If you’re in doubt, remove the valve and tap the inlet side on a clean bench. If any debris comes out of the valve, you can be pretty sure you’ve found the problem and should consider replacing the charcoal canister.

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Another problem we’re seeing with the 2.3L ­engines is a bit more serious and will lead to poor performance and a no-start complaint. These timing chain-equipped engines have been having a problem with the cam timing shifting when the oil level gets extremely low. In a perfect world, everyone checks the oil and gets timely oil changes, but we all know that’s not always the case.

These engines use friction washers (that must be replaced when removed) to hold the cam and crank gears in place after using special tools to establish the cam timing. While this system ­allows more precise timing, it has to be considered while you’re diagnosing a no-start, low power or crank and cam sensor codes. It’s apparent the cams are momentarily seizing due to the lack of lubrication and the gears are slipping. It’s also important to keep this system in mind if you’re going to replace a crank seal.

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