A look at diagnostics and repairs of European vehicles

It is important to make sure that the Monitors are Ready to confirm your repair. Many techs do not understand how important Monitors are. When a Monitor is Not Ready you do not know if you’ve fixed the drivability problem on the vehicle. On Audi/VW products (and a few other OE's), you can run the Monitors to Ready right from your scan tool, to check the vehicle systems out faster (Figure 1). I usually recommend performing this step so a test drive can illuminate the MIL quicker, confirming the vehicle repair was successful or not. On this Jetta, the vehicle was indeed repaired since the MIL stayed off.

The customer was happy and drove away, but it would not be the last time that we see this VW. At 165K miles, the vehicle returned with the MIL illuminated again and, a Jetta owner that was not sure that we had repaired the Jetta correctly. We explained that we would diagnose the vehicle and if the same DTC for the O2 Heater circuit was the cause of the illuminated Check Engine light, we would repair the vehicle, free of charge.

Don’t you just love it? Once you touch it, some customers want you to own it and repair everything for free.

Following a complete vehicle scan, we uncovered a P2177 (System Too Lean Off Idle) that could mean that the engine has a fuel delivery problem (Figure 2). The first place to start is by checking the fuel trim numbers. If you don't own an ATS EScan than you not only need to look at fuel trim numbers but, you need to find out what fuel cell the DTC has set in. Since we do have the EScan, it’s easy for us to identify what fuel cell the problem is occurring in. If the fuel trim block numbers are high/positive at the lower-end than, it’s a vacuum-related problem. If it’s high at the top of the chart the problem is fuel delivery (that could be a clogged filter, voltage drop on the fuel pump circuit or, a bad fuel pump). If neither one of these exist and the chart has high fuel trim numbers from bottom to top, than the problem is a load sensor (Figure 3).

Figure 3

Jettas use a MAF sensor so, the next logical test to perform would be a MAF sensor volumetric efficiency test (VE test). On the EScan, we selected the VE test and ran it, confirming that the MAF sensor had an issue (Figure 4). The MAF sensor on this engine cannot be cleaned so, the only path of repair would be to recommend a rebuilt or new MAF sensor. I am not a fan of the rebuilt sensor since many of them will not perform correctly (we learned by experience). After we printed out and provided the test results to the VW owner she understood and gave us the OK to repair the vehicle (That old saying “paper sells,” is true). We always provide a printout or electronic copy of the diagnostic report so, the vehicle owner can see the before and after difference. In this case, it helped keep the Jetta owner calm, rather than her blaming us for not diagnosing and repairing her vehicle properly.

With that out of the way we still needed to explain that a 165K mile vehicle will have parts that have worn or gone bad. Since this VW engine had a lean condition there was a change that the P2177 (System Too Lean Off Idle) could cause a very rich mixture, taking the catalytic converter over the edge and illuminated the Check Engine light (again, setting a P0420 DTC). Lucky for this Jetta owner, after the MAF sensor replacement and a couple of road tests, the VW was DTC- free.

A 2005 BMW X3- MIL/misfire

A 2005 BMW X3 3.0L at 178K miles, came in with a complaint of a check engine light illuminated and an engine misfire. This “Bimmer” was in bad shape but, we were told only to diagnose and repair the engine misfire. We followed the X3 owner’s wishes and concentrated on the problem at hand. After we spoke to the X3 owner we were as much in the dark about the problem on this X3 as we were, before we asked him. Our game plan on this vehicle would be to perform a visual inspection and follow-up with complete system scan. The visual inspection provided us with an abundant amount of problem-areas, such as:

- exceptionally low engine oil

- missing air filter

- loose spark plugs

- missing passenger seat

- metal-to-metal front brakes

The interior of this BMW resembled a garbage dumpster (debris everywhere) along with dirty windows (that I could barely see out of) and, a messed up clutch pedal (it was missing the rubber pad and exhibited a noise, with the pedal depressed). The first thought that came to my mind was "do I really want to work on this car?" After some more thought I realized that this sloppy-mess is not the type of vehicle we work on at our shop, AutoClinic. I had to come to the reality that the vehicle owner was the son of my HVAC-guy. I could not be rude so, as all good techs must do, I just had to get over it and move on to diagnosing and repairing this mess.

Figure 5

After we got over the condition that this vehicle was in, we started diagnosis by scanning the vehicle with our AutoLogic. We then switched over to the Snap-ON ZEUS scan tool. As can be seen in Figure 5, the following DTCs in the Engine controller (DME/DDE), were uncovered:

- 27C3 (Thermal Oil Level Sensor)

- 2882 (Mixture Preparation, Bank 1 Mixture Too Lean)

- 2883 (Mixture Preparation, Bank 2 Mixture Too Lean)

There were DTCs found in other systems such as Antilock Brakes, Airbags, AC, and Transfer Case but, we were only concerned with the engine issues. My technician, “Franklin,” took the next step by looking up all the information associated with the oil sensor, before moving on to the lean-condition. Franklin already knew that the engine oil level was low, so he added the correct amount to protect the engine and eliminate the possible cause of the oil level sensor fault.

As you can imagine, the problem was not solved yet. Through testing,  Franklin came to the conclusion, the oil level sensor was defective. He ordered the oil level sensor and when it arrived, installed it. This solved the oil level  DTC issue. Franklin was now able to move on to the lean-condition issue. He switched to our favorite scan tool for drivability, generic DTCs and fuel trim,… the EScan, by ATS (Figure 6) . It was found that the fuel trim numbers were way off. As you can see, the chart indicated high positive numbers, from the bottom of the chart to the mid-level. If this engine was running better, it would have revved higher and, the fuel trim cells would’ve populated the chart to the top, rather than just the middle. Franklin asked me what I thought of the readings and I confirmed his diagnosis of a bad load sensor.

I called the customer up and told them that we were far from done with diagnosing the engine problem but that we needed to start by replacing the MAF sensor. With the X3 owner's approval, we ordered and installed a new MAF and rechecked the engine’s performance and fuel trim readings. As a result of the check, we found a reading of -20 and -18 fuel trim (at idle) that went away, while we increased the load on the engine. The results confirmed that the replacement load sensor fixed the high positive fuel trim number (that we had before) but why did the computer command such negative numbers after the repair?

Figure 8

We thought that we would reset the adaptive fuel trim and take the vehicle for a good test drive. When we returned to the shop the fuel trim numbers were still a very-negative number but, only at idle. When fuel trim numbers are commanded negative it usually means that there is an unwanted fuel source (such as leaking injectors, high fuel pressure, EVAP purge issue, contaminated engine oil, E85 issue, or other). Franklin and I check everything and came up empty. We needed to regroup and try to figure out what is causing the -20 and -18 fuel trim readings (Figure 7). When both banks of trim are affected there has to be a common point so, we decided to smoke-test the engine to see if there were any leaks. You won’t believe what we came up with! A dipstick seal that was leaking (at the base of the oil tube) and contaminated engine oil (Figure 8). We installed a new dipstick o-ring, changed the engine oil and filter, reset the additive fuel trim and, test-drove the vehicle. When we returned, we connected the EScan and checked the fuel trim reading again. We found that the BMW was now back to a normal under all operating conditions (Figure 9). Now, at least the engine of this X3 was running as designed. There was still other worked that needed to be completed, to get this pile-of-junk back to normal. 

2006 VW GTI 2.0L turbo-MIL

Our next vehicle was the complete opposite of the X3. This 2006 VW GTI 2.0L turbo with 46K miles, is just one (of 5 vehicles) that this customer owns. Let me tell you that this GTI looks better than when the vehicle was purchased new. All of her vehicles are very well taken care of and are a pleasure to work on. Anytime there is even a minor issue on the vehicle, the owner is right on top of it and, brings it in for repair.

This visit to the shop was for concern of an illuminated Check Engine light and her (2000 miles or less) synthetic oil and filter change. We started by following our normal diagnostic plan and asked when she first noticed the Check Engine light to be illuminated. We inquired if she just refueled the vehicle or if there was there something else done, that could have caused the problem. We connected our EScan and found a P0301 along with the associated Freeze Frame data. We found all of the system readiness Monitors being Ready, also (Figure 10).

Examining Freeze Frame data provided us with the information on when the P0301 had occurred. The engine temperature was at 50 degrees Fahrenheit with an engine RPM of 1185. This is important information. Since the engine was not currently misfiring, we needed to duplicate the problem. With Freeze Frame info, we knew that we had to have the engine cooled- down, to check for the misfire since, none were present with the engine at operating temperture. We left the vehicle outside/overnight and made sure that we would have all our tools ready, when we started the engine up, in the morning. The tools we would use were the EScan and the GTC505 ignition tester.

Figure 11

We unlocked the vehicle, popped the hood, connected the scan tool, and fired the engine up. Our patience, in  waiting until the engine was cold paid off. The engine started to misfire for us. To rule out a mechanical-fault condition, we ran a Relative Compression test on the EScan (Figure 11). Next, “Bill” powered up the GTC505 and started testing the ignition system, finding that the number-one cylinder was misfiring, when the engine was cold. Bill removed the coil and spark plug, only to find that there was some carbon on the spark plug electrode. He advised the vehicle owner to perform a GDI (Gasoline Direct Injection system) cleaning, since the spark plug tested good. This was determined by moving the plug to another cylinder that was not misfiring.

The customer decided that she would take the VW and drive it, to see if there would still be an issue. We were surprised by her decision (considering she always wants her vehicles in “tip-top” shape)! We cleared the DTC and had her drive the vehicle and, return to check it out, in a couple of weeks. Upon the VW’s return, we connected the scan tool and found that there were no DTCs or Pending DTCs and, all  Monitors were Ready.

We assumed that the misfire was caused by the carbon build-up that affected the number-1 cylinder, when it was cold. The problem cleared up when Bill removed the spark plug, to check for an issue, before installing a pressure transducer for a compression test. The results of the in-cylinder transducer test did not reveal any mechanical problem so, that only left one thing to check. We had to wait until the engine cooled-down before using our video scope so, we would not fog the lens or ruin the video inspection camera. The inspection with the video camera uncovered heavy carbon build-up that we have seen before, on other GDI engines (especially Audi and VW). With the video screen shoots, we explained to the owner that a GDI fuel system cleaning was needed to prevent the engine from misfiring in the future. The owner (for some unknown reason) decided not to perform the cleaning at this time. Again, were a bit taken back by this decision. Maybe it was because of the pandemic and, that she had just had us perform two clutch replacements (one on this GTI and the other on her Audi). Anyway, we are still waiting for the MIL to illuminate again (since theses 2.0L turbo tend to build up carbon up and cause misfires). Only time will tell…but, I’ll bet that this VW will be back with an issue soon!      

I hope these few European case studies shed some light on helping you diagnose problem vehicles. Remember no professional team plays a game without a game plan and neither should you.