Refine your game plan with a logical process to diagnosis

June 1, 2019
With vehicles becoming more and more complex, we need to have the proper training, tools, equipment and a logical diagnostic game plan.

If you have been reading my articles the past 10+ years, you know that I always emphasize having a Game Plan. The New England Patriots would not have won the Super Bowl again if they did not have a plan. We’re not a football team but we are a team of professionals who keep America running. With vehicles becoming more and more complex, we need to have the proper training, tools, equipment and game plan. In this article, I will take you through a couple real life case studies that hopefully assist you in diagnosing problem vehicles.

First up — An ailing Audi

Our first case study that came in was from a customer who had recently purchased a 2006 Audi A6 3.2L from his uncle’s used car lot. However, this well detailed Audi had to be towed in due to a no crank or start condition.

Sometimes Audi models can be a real challenge to diagnosis and get running if you don’t have the proper training and scan tool such as Ross Tech or ODIS. After questioning the vehicle owner (who unfortunately did not yield much information), it was time to move on and use our best tools. The tools that I am referring to are the tools are the same you've heard me preach on before - the tools that God provided us with; our brain, eyes, ears, nose and hands. As a result of using those tools we found that the steering wheel and column may have been compromised.

The battery and starter checked out fine. Having had previous experience with a similar problem on Audi and VW, we suspected an issue with the Access / Start module. The results from the ODIS scan tool confirmed our suspicions of a problem relating to the steering column, yielding a large list of DTCs. One of the DTCs that had to be dealt with first was the 0005 Access/Start Authorization System.

Figure 1

This DTC prevents an engine crank/start condition because it brings down the CAN BUS (Figure 1) and shuts down other modules. The Authorization Module is integrated with the immobilizer and steering wheel lock mechanism that is mounted to the steering column. Our experience with this issue has shown us that the module is a common problem that causes no response from the ignition key or start button. The module’s job is to look for the key or transponder that manages unlocking and locking the steering wheel. It also activates the relay’s terminal 15 that supplies power to the other modules in the vehicle. If an issue is detected with any of the module components such as the actuator motor, sensing micro switches, relay, or other electrical connections, the system will throw a DTC and not operate.

Figure 2

The Audi dealer’s only sell the complete steering column to repair this problem, but that’s not the only way to fix this problem. For one, the module can be removed without completely taking down the steering column. Now it was time to contact the vehicle owner and explain the repair options so he could choose the path of repair that works best for him. This was followed by providing the Audi owner with pictures and other printed information (Figure 2) on his no crank/start condition. In this case we explained that the engine not crank/start condition was due to a "no com" (communication) problem on the CAN BUS. We continued with an explanation of the different repair options; either replacing the complete steering column or just removing the Access/Start module and sending it out for repair.

The difference in pricing significant. A new steering column from Audi goes for $1700.00 while the other option is about half the price. After our explanation to the vehicle owner and the used car lot uncle, they decided that cheaper was better. However, their choice came with one big surprise! They decided to tow the Audi back to the used car lot shop. So, they used us to diagnose the problem and chose a cheaper alternative by performing the physical repair at the used car lot.

We invoiced the Audi owner for the diagnosis while they prepared to have the vehicle towed. After seeing the damage they previously inflicted to the steering column, we suspected that they would encounter problems and be back again. The used car lot apparently proceeded to remove the module and, as we suggested, sent it to When a module is at they check the circuits, cleared out data and format the module so it mimic’s a new one. After the used car lot shop received the reconditioned module, they installed it but encountered the same no crank/start condition.

They decided that they were in over their head and called us, asking if they could tow the vehicle back to our shop and get it running. Bill explained that there would be another diagnostic fee along with a programming fee to get the Audi running. Once the vehicle arrived, we looked it over, paying special attention to the steering column area. Bill noticed that the used car lot did not follow directions of only removing the module. Instead, they totally removed the steering column. As a result of their removal process of the steering column, there was more noticeable damage - including a "click" noise from the steering wheel that was due to a damaged clock spring.

Figure 3

Bill called the used car lot to inform them what we uncovered before proceeding to do anything on the Audi. Their response was don’t worry about the damage just get the Audi running. Since they gave us our marching orders, we proceeded first with a full vehicle scan. The results of the scan uncovered (Figure 3) the following DTCs; P1674 Databus Drivetrain Implausible Message from Instrumental Cluster and FAZ1225E error with serial number, (Figure 4) Error: MSG serial no. is not associated with VIN.

Figure 4

Our next step was to try and clear the DTCs then insert the correct VIN in the module. After the programming process was completed the engine came to life and ran well. We followed that up with another complete scan of all the vehicle system making sure there were no other issues. It always good practice to make sure all vehicle modules are clear of DTCs before returning the vehicle back to the owner. With the Audi now starting and running it was time to collect our diagnostic and programming fees and return the vehicle to the customer.

Next - A weak Chevy

2009 Chevy Impala 3.9L 54K came in with a complaint of low power, poor stopping and the Check Engine light illuminated. The customer told us this only happened after her son was driving over 95 mph with the police in pursuit!

She said that her son had to make a rather quick stop as the police had blockaded the road ahead. After absorbing what the vehicle owner provided us with, we concluded that a good visual and mechanical inspection was the first place to start. My tech, Franklin, was given the job and thought he would take the vehicle for a short test drive. After Franklin started the engine up and discovered that it was barely idling along with the brakes feeling bad, he thought that a test drive was out of the question. The vehicle was barely driven from the front of our shop into his bay.

Figure 5

As Franklin was driving the vehicle into the bay, he noticed that it was very difficult to stop. He thought that the poor idling and stopping could be caused by a massive vacuum leak resulting from a very lean condition. He decided to connect the Snap On Zeus scan tool since it performs a full vehicle system scan rather quickly. As a result of the Zeus scan (Figure 5), he found all of the vehicle systems to be DTC free except for the engine that had a DTC P0171 stored. Take a look at the scan data (Figure 6) that Franklin uncovered as the engine stalled from a high rpm. Anything stick out as being a problem?

Figure 6

For one, the O2 voltage was switching as the engine rpms were raised up but were down to zero near idle. The next important PID data was LTFT reporting +30 and it was captured in fuel cell 14 at a high rpm. Normally if this was a vacuum leak at idle. the Fuel Trim cell number would be a 0 to 6 number rather than anything higher. His thinking at this was point was that the engine maybe starving for fuel since one of the major complaints was low power. Franklin proceed to test the fuel pump current waveform at the fuel pump relay, pins 30 and 87, and found the current ramping waveform was normal at 6 amps. He followed that by performing a fuel volume test with our MAC/MityVac fuel pressure and volume tester. The results of the fuel pressure test were a perfect pressure of 62 psi and a volume reading of 0.5 gallons per minute without any bubbles or fuel discoloration in the sight glass. Now he could rule out a fuel delivery problem and concentrate on finding out what was causing such a huge command of 30% LTFT.

Figure 7

His next step was to remove the Zeus and install the EScan since it provides more in-depth information on driveability problems. The EScan data revealed the same DTC P0171 (Figure 7) with the very important Freeze Frame data. The Freeze Frame data is like a snap shot picture of when the engine acted up and threw the DTC. In this case, we can see that the engine was hot, not moving since mph are 0, MAP at 14 HG, MAF 3.2 lower than the 1 gram per litter at idle and rpm at 588, STFT 35% and LTFT 29%. Now this information warrants further investigation that led Franklin to the (Figure 8) Escan Sharp Shooter Fuel Trim data. He could now view the trim data in a graphic format rather than just as a static number. The fuel trim numbers were high at the low rpms and a bit higher on the chart than idle since the engine would stall out at a normal idle speed. We noticed at this point that the high numbers were not just at idle but up at a 70% throttle and about 4000 rpms. Normally if the numbers are high on the low end of the scale and high all the way through the rpm and absolute throttle ranges, it’s a MAF problem.

Figure 8

But hold on, we have an engine that will not run at idle. This made us think that there had to be a massive vacuum leak. Franklin began to unplug all the engine vacuum lines and sealed them to see if there was any difference. He removed the PCV valve and noticed a slight difference, so he installed a new AC Delco PCV that resulted in the engine to somewhat idle, but the LTFT (Figure 9) was still high.

Figure 9

At this point we thought that the next logical area for such a large leak was at the intake manifold. I took out our leak detection tool that consist of a Coleman propane bottle, valve assembly and flow tube. With the valve fully opened for maximum propane flow, we checked for leaks. In the past, we had come across some intake manifolds on these engines that had gasket issues as well as a PCV valve problems. Working as a team, we checked all intake areas and came up empty, no detectable vacuum leaks anywhere on the engine. The next thing we tried was flowing propane to an open vacuum port and found that the engine was able to idle better. With that result, we confirmed that there had to be a leak somewhere, since adding propane allowed the engine to idle better and the fuel pump passed pressure and volume test.

Our next step was to shut the engine down and connect a smoke machine. Unfortunately, the smoke test did not reveal any leaks, coming up empty handed we thought it had to be something that we were overlooking. I carefully thought about a couple of GM police cars that I had worked on right after 9/11. Those engines had a similar issue that resulted in a vacuum leak that were also difficult to locate. The problem with those vehicles was that the power booster diaphragm was defective causing the high fuel trim readings. I mention that to Franklin and had him smoke the power booster to check for escaping smoke. The test yielded no leaks, so we were still no further along locating the leak.

Franklin called me back over to get me up to speed and brain storm our next move. Thinking how there was a possibility of hydrocarbons being in the brake booster diaphragm if the filter diaphragm was leaking, there was a good possibility of the smoke being consumed and not being visible. We switched from shop air to CO2 on the smoke machine and tested for leaks using the Bullyseye leak tester. The testing along with using CO2 uncovered the leak in the power booster.

As we depressed the brake pedal, we noticed that the leak would be worse or nonexistent at times. I assume the reason for the different reading was that the power booster diaphragm was flexing causing the leak to be worse or better depending how it flexed. We blocked off the power booster to confirm our finding then ordered a new booster. Franklin removed the old power booster and install the new one that resulted in a normal engine idle.

Figure 10

With the engine now running normal, Franklin connected the GM Tech 2 and reset the Adaptive Fuel Trim. The Adaptive Fuel Trim resets (Figure 10) the fuel trim so the engine will not continue to add a high commanded rate of fuel. Remember after any Fuel Trim repair an Adaptive Fuel Trim reset is needed to get the engine fuel delivery commands back in a normal operating range. This is an important step that is commonly overlooked that can cause other problems such as a P0420 to pop up. The rich condition caused by a command that has not been reset can take a border line converter and push it over the edge. After the repair, the fuel trim reset, along with a good test drive it was time to recheck the vehicle for DTCs and fuel trim readings. Since the Tech 2 was left connected for the fuel trim reset it was taken along for the test drive and used to recheck the vehicle when it was returned to the shop. The LTFT readings were now back to normal along with a stable idle and good brakes.

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