Scope & Scan - Service Repair

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Plugging all the leaks

This month we look at avoiding the return of the MIL light and tips on leak detection.
Friday, August 1, 2014 - 07:00
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New DTCs appearing after a repair is more common than you might think. The reasons why are several, but the most common are a failure to make sure all the OBDII test monitors are Ready, failure to address pending Diagnostic Trouble Codes (DTCs), and not investigating the cause of Mode $06 failed test results. Let me provide you with a few examples that will shed some light, while helping you better understand why it’s so important to perform a complete and thorough diagnostic procedure on an OBDII vehicle.

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The screen captures (Figure 1) are from a 2006 LR3 with a 4.4 L V8 engine that came in the shop with a Mass Air Flow (MAF) sensor P0101 DTC. Along with the code, I found that not all of the monitors had run to completion. While performing my diagnostic procedure on this vehicle, it would have been easy to make the ultimate mistake of getting tunnel vision and just concentrating on the MAF DTC. But by looking at the monitor status, I could see that there were two monitors (the O2 and Evaporative Emissions (EVAP)) that were listed as incomplete or Not Ready. The one that I was really concerned with was the O2 monitor, because the O2 sensors are used to check other systems on the engine. I looked up the Drive Cycle criteria for the O2 monitor and that seemed easy enough to run (Figure 2). Always start with the easiest procedure first. Before checking or repairing the MAF circuit problem, I took the vehicle for a ride to see if I could get the O2 monitor to complete.

Because the engine was already hot, I knew that the EVAP monitor would not run until the vehicle cooled down, so there was no sense wasting time at this point to even try. The O2 monitor status can affect the EVAP monitor. It’s always a good idea to read up on how the system and components function and interact no matter how many times you may have worked on a particular manufacturer’s product line.

In this case, we need to know how the Engine Control Module (ECM) is running the EVAP monitor. The O2 sensors are used to check if the EVAP system is actually purging HC (hydrocarbon, or raw fuel) vapors on this vehicle. There always are checks and balances to insure the systems function as designed. The EVAP purge valve (normally closed) is commanded open by the ECM which is looking for a change in O2 voltage to make sure the EVAP system is working properly. Understanding how the system functions is a smarter and quicker way to precede.

After driving the vehicle for 15 minutes and following the drive cycle requirements, the O2  monitor did not complete. While performing my troubleshooting, I found a few problems that prevented that monitor from running. The first problem that needed to be addressed was a cooling system issue. The thermostat, coolant sensor and overflow bottle all need to be repaired or replaced. I installed a new thermostat, gasket, coolant sensor, coolant bottle, level sensor and bled the cooling system. I followed that repair with a check of the O2 sensors using a labscope, confirming that they were working properly. Now that I knew the sensors were good and all the basics were good, I fully expected the monitor to run, and it did.

With the O2 monitor Ready, I was able to test the system. Take a look at the DTCs that came up as a result (Figure 3). As you can see, the ECM now displayed five DTCs instead of the one that had been previous been displayed. Not only did the monitor confirm the P0101 MAF sensor DTC, it was clear that the O2 sensors were sensing failing conditions that were ultimately caused by a cheap aftermarket replacement MAF sensor.

As you are reading through this case study, you can see how very important it is to have the monitors all run to completion. It is vital to confirming your repairs and avoiding comebacks caused by codes that appear after your initial fix.

Finding Tough A/C Leaks
It’s summer time and the A/C season is upon us! A/C season can be a short window of opportunity for some because not every one of us lives in a warm climate all year long. For us who braved this cold winter weather, it feels good to finally get some hot weather. That being said, most motorists expect their A/C system to keep them cold and comfortable when it’s hot outside. So when their A/C system does not function, we get the job of diagnosing the problem. This is one repair that price does not seem to matter as much since the owner just wants to be cool.

As you know from working on A/C systems, there can be numerous problems causing no cold air from the ducts. Low refrigerant, defective expansion valves or office tubes, defective compressors, leaks, contaminated refrigerant or sealant problems are just a few. Most of the time, if you have a good game plan on how to check and diagnosis the system you can stay out of trouble. The first thing to do is use a sealant detector so you can make sure that you refrigerant identifier and AC machine do not get contaminated. With that very real possibility out of the way, next check the refrigerant itself with an identifier for the same reasons.

How about A/C leaks? There are many methods for identifying system leaks with all of us familiar with the refrigerant leak detector, fluorescent dyes, ultrasound equipment and nitrogen testing. Even with these methods, finding the really small leaks is always a challenge. And considering how little modern systems hold, finding the little leaks is important to not only making sure our customers stay comfortable, but their system compressors to live a long and happy life.

One solution is available from Automotive Test Solutions (ATS). The tester that ATS offers can find the smallest leak in the A/C system and is also useful for finding leaks in nearly any system on the car from EVAP systems to tires.

Here’s a great example of a 2008 Acura RDX 2.3L Turbo I recently had with a complaint of poor cooling from the air condition system. The vehicle was brought to the dealer before coming to us because of a recall that matched the owner’s complaint. The dealer recall (12-039) is for an A/C compressor extended warranty that addresses poor cooling caused by compressor performance. The vehicle owner was told that the compressor was replaced and fluorescent dye and refrigerant were added.

After the repair, the system was performing well for about a month before it went back to blowing warm air. The vehicle was returned to the dealer and rechecked for leaks but none were located. The system was recharged and returned to the customer. After another month, the owner experienced the same problem, but this time they brought the vehicle to us. We checked the system for the proper amount of R134a and found the system was free of sealant, was 100 percent pure R134a, but that the system charge was low. Our next step was to check the system using a new SAE J2791 leak detection sniffer able to detect leak rates of under ¼ ounce per year but had no luck locating the leak. We tried checking for signs of the dye the dealer had installed using a black light that works on all dye spectrums but still could not locate the leak.

We recovered and evacuated the system and used the ATS BullsEye system, pressuring the A/C system with CO2. CO2 is a smaller molecule and more easily passes through small holes, making it easier to detect. Using the special leak detector that comes with the kit, we located the area of the leak in the car’s condenser (Figure 4). To confirm the small leak, we sprayed the BullsEye foam on the area where the BullysEye detector had triggered. As you can see (Figure 5), the pink foam (area of no leak) reacts with the CO2 and turns yellow, confirming the leak. A new condenser and receiver drier (one complete unit) later, and this customer’s problem was solved. 

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