A game plan for diagnostic success

May 24, 2016
In order to find a vehicle problem, a technician must be prepared to interrogate the vehicle owner and address their concerns.

In order to find a vehicle problem, a technician must be prepared to interrogate the vehicle owner and address their concerns.

The following should all be a part of your diagnostic game plan: a vehicle test drive with the vehicle owner (if possible), a visual inspection and a check of all the basics — battery, fluid levels, complete vehicle system scan, and service information, including TSBs. Asking the right questions such as those to better determine when does the vehicle exhibits the problem — when cold, hot, after sitting awhile, on a rough road, at a certain speed or while backing up — all will help you narrow down your search for what maybe the problem.

Figure 1 Figure 2
Figure 3 Figure 4 Putting a stop to the problem Years ago I had a vehicle that was dropped off from another shop with a complaint of a rough-running engine only when the vehicle was at a stop or on bumpy roads. This vehicle had a bunch of new components in it including new plugs, plug wires, air and fuel filters, fuel pump, injectors and even a PCM. While I performed a visual inspection, I noticed that the brake pedal was worn on the side facing the throttle pedal, along with a hole in the carpet. This visual indicated to me that the owner (who I never met or spoke to) most likely wore work boots or a shoe with a hard sole. The next thing I observed was that the engine started right up and ran at a normal high idle before dropping down to a smooth normal idle. After applying the brake pedal while I was selecting the D range on the shifter, the engine began to run rough until I started to drive the vehicle. With my foot off the brake, the engine ran smooth; but once I pressed on the brakes, the engine ran rough again. I thought that this may be a problem with fuel delivery even though the vehicle already had a new fuel pump and filter installed. Since this vehicle had an accessible fuel pump relay, I thought that I would current ramp the fuel pump to see if the amperage was at the normal level of 6 amps. Once I installed my amp clamp on my labscope I found that the pump current ramping waveform was normal at idle. When I pressed on the brake pedal the engine ran rough and the amperage dropped to about 3 amps. I tried applying and releasing the brake pedal multiple times only to come up with the same exact results. My next step was to look up the wiring diagram for the vehicle circuit to see what the common denominator was. What did the brake pedal and the fuel delivery have in common? It was G402 (Figure 1) ground, which had 16 loads (light bulbs), including the fuel pump, on the same ground circuit.

I used the wiring diagram like you would use a map to find what road to take. I found that G402 (Figure 2) was located in the trunk on the left rear wheel housing. When I located the ground, I noticed that the area it was attached to was badly rusted. To confirm that the ground was the problem, I connected the ground pigtail that is attached to the Power Probe handle to the existing ground and depressed the brake pedal. The result was that the engine no longer ran rough with the brake pedal depressed. Since connecting a good ground confirmed that the engine ran smooth while the amperage stayed at 6 amps, I knew that all I had to do was clean up the ground terminal ends, along with the star washer and bolt and relocate the ground to a rust-free area. After I located a good rust-free area, I cleaned it down and installed the bolt, star washer and ground wires followed by applying the brakes again. Now there were no signs of a rough-running engine.

A game plan with coolant temperature Let’s take a look at a cooling system issue on a 2003 BMW 535xi that has an illuminated MIL along with a P0128 (Coolant Temperature Below Threshold) DTC. When this 535xi came in, the vehicle still had good heat and the engine was not overheating. Most of the time when we think of a cooling system issue there is either a problem with the vehicle not getting enough heat or worse yet, it's overheating. Since this vehicle did not exhibit either of theose problems, we had to look elsewhere for answers. One good place to start since this vehicle had an illuminated MIL is checking out Freeze Frame (Figure 3) to see important information that may lead us to the heart of the problem. Unfortunately, the Freeze Frame data did not reveal any important clues. However, we did notice that the temperature was only at 177°F/88°C when the DTC was set. Our next step was to check the time to temperature to see if the cooling system could reach the desired temperature within a specific amount of time. We connected the EScan, the only scan tool that provides important information on Time to Temperature by testing the cooling system. While performing this test using the EScan, the user is able to see if the thermostat or cooling system has a problem.

The graph in the middle of Figure 4 shows that the temperature starts high but drops rapidly over a short period and then only rises a small amount. The test does not even display a time in seconds in the upper right corner for the raise time as it should.

Figure 5 Figure 6
Figure 7 Figure 8

Now let’s take a look at the Time To Temperature screen (Figure 5) after we replaced the thermostat, added coolant and bled the system. The temperature rise is now a smooth line that reaches 199°F/93°C in 0.12 seconds. Also notice that the DTC from the first screen (second box from the bottom left of the scan tool) that was in red is now yellow, which means that the DTC has gone from a hard DTC that turns the MIL light on, to one that is now pending. Remember an illuminated MIL can turn off if the conditions that caused the DTC are met and it passes certain OBD II criteria or trips.

Now let’s take a look at a vehicle that has a cooling system issue that did not set a DTC. One such vehicle that came in was a 2009 Honda Pilot that had an illuminated MIL with a P0420 (Catalyst System Efficiency Below Threshold Bank 1) DTC and a Pending P0430 (Catalyst System Efficiency Below Threshold Bank 2).

Let’s see what clues can lead us to the problem. Take a look at the Freeze Frame data and note the engine temperature when the DTC was set. Because the engine was on the cool side, it caused the engine to run richer for a longer period and thus set the current DTC. There are other causes for a rich condition, but when we take a very close look at long-term fuel trim (LTFT), we see that they are at 4 and 6 in the Freeze Frame data. 

Take a look at the RPM and low load of fuel trim (Figure 7). Note that it continues to be high all the way through the cell blocks. There are a few causes for these high numbers, such as the Mass Air Flow (MAF) sensor (another shop already replaced the sensor with a new OE sensor), fuel delivery and temperature.

Looking at the Time To Temperature test (Figure 8), we see that even though the passenger compartment was getting heat and the engine was not overheating, we had a problem. The rise to operating temperature was too slow, which caused the engine to stay in a colder range that requires more fuel. Over time, rich mixtures ruin catalytic converters. In 135,739 miles/218,450 km, the thermostat and coolant were never changed, which helped “kill the cat.” The fix for this vehicle was to replace both converters, flush the cooling system, replace the thermostat and tune up the vehicle.

No crank, no start Audi
A 2007 Audi Q7 was towed in from an Audi dealer with the symptoms of no crank, start and transmission shift selector that would not go into park, preventing the ignition key from being removed. When this vehicle was towed in, it had a noticeable yellowish plastic (Figure 9) cover on the front windshield and hood. This indicated to me that the vehicle was taking on water, but then again it not much different than most other European vehicles. The dealer diagnosed the vehicle with a wiring problem and gave the owner an estimate of more than $18,000 to fix the vehicle with no guarantees. The vehicle owner had already installed a new battery and had tried to get it repaired somewhere else prior to towing it to the dealer. What amazed me was that the dealer charged the owner thousands and yet was not able to get the engine cranking, running or even get the shifter to move to park.

The other overlooked area that the dealer did not address was that they did not code the new battery to the vehicle computer system. This was a simple process where we use our Autologic to code the battery and check the system. After checking all the vehicle systems to find out why there was a no crank, no start, it was time to dig in and start checking powers and grounds. My lead tech Bill found extensive water damage to the main underhood fuse box (Figure 10) that houses a bunch of fuses and relays. As you can see from the picture, the water damage was a result of a leak over time. Since the damage was contained to this area, Bill started checking and cleaning the nonexistent powers and grounds, along with replacing all of the fuses along with some of the relays (Figures 11 and 12) that had internal corrosion. There were other relays that did not need to be changed since they could be cleaned. To ensure problem-free connections, Bill applied Stabilant 22 to all the wiring connections and terminals in both the fuse and relay boxes. After Bill completed the cleaning and replacement procedure, the engine was able to crank but still did not start. However, even though the engine would not start, the transmission shift selector could now be shifted into park and the ignition key could be removed. With the problems being narrowed down, Bill once again checked the complete system using the Ross-Tech scan tool. What he found on this vehicle that only had 67,300 miles on it was amazing. The Ross-Tech system scan came up with more than 15 modules reporting (Figure 13) serious malfunctions.

Figure 9 Figure 10
Figure 11 Figure 12 In order to provide some proper guidance and get another set of eyes on the problem, Bill contacted Ross-Tech tech support and reviewed the complete system log. On a vehicle that had so many problem and extra set of eyes is always a good move. Unfortunately tech support was unable to provide Bill with an exact fix and said they had not seen anything like this. Since I was on the road teaching I was not able to be there from the beginning, so I asked Bill to get me up to speed. After trying multiple tests and looking over the vehicle, I came to the conclusion that the ECU/PCM was not always providing information. This is why it a good idea to always have at least two scan tools in your shop to make sure it’s not the scan tool. With two scan tools showing me the same results along with all power and grounds now in good condition, I decided to call for a new ECU/PCM. The price and availability for a new ECU/PCM was about $2,000 and 10 days to get. Instead we called AutoPCMs.com and we were able to get one overnighted for under $500.Once the ECU/PCM arrived, we had another problem, since the ECU/PCM needed to be programmed along with aligning the immobilizer security code to other vehicle computers. Since I already had an LSID (Locksmith Identification Number) that I signed up for on the National Automotive Service Task Force, I was now able to apply for the Audi license for the ODIS factory scan tool that is need to perform this task. The process took a few days after I signed up on the Audi/VW website, so we were lucky that the vehicle owner was able to wait or we would have lost this job. After receiving the Audi/VW approval, I was able to download the latest software and go in and see (Figure 14) all the modules that were preventing the vehicle from starting. Now it was time to program the unit and align the security on all the modules, but it was not going to be all that easy. Having used only the older version of ODIS in the past, I was not familiar with the new version and how to program the vehicle from the ODIS diagnostic portal. Since I have Autologic tech support, I contacted Justin who was able to connected me to an Audi/VW specialist. When the specialist called me back, he logged onto my laptop and walked me through the new process of programming the vehicle. What he showed me was that I could not be in diagnostics and select programming without first existing diagnostics. After a lesson learned, all of the modules (Figure 15) except one (the TPMS module that needs to be replaced for a different reason) were now confirmed good and working. It’s a good idea to network with others and have a backup since it’s impossible to know everything. Many times when I am teaching a class a tech will say to me, “You know everything.”

“I only wish I did,” I respond. I only have a "G" and a half of "o" and I will never get the other half of "o" or "d" since only God knows everything.

If we use quality tools, get training and use resources such as ALLDATA, Mitchell1, Motologic, Identifix, iATN, Google, YouTube, hotlines, each other and most importantly our brains, we will find the best route in diagnosing and repairing the vehicle.

Figure 13 Figure 14 Figure 15

A closing note
I think it’s important for each shop to have a technician who is trained and has an LSID license, and if you work on Audi/VWs, you need their license as well. In 2017, some things in our business are going to change for the technician who works on drivability problems. In order to program all vehicles, the standard is going to utilize a J2534 device, such as a Drew Tech CARDAQ M that will be the hardware interface for the OE’s full-factory scan tool. If you think that you are just going to replace a computer in a vehicle and use your current scan tool to get the vehicle running, you are mistaken. Don’t wait until the horse is out of the barn; get involved, trained and go to www.NASTF.org and start the LSID process so you can diagnosis, program and fix vehicles.

About the Author

G. Jerry Truglia

ASE World Class Triple Master Technician Auto, Truck & School Bus, L1, L3, F1, A9, X1 C1

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