Test, don’t guess, when diagnosing a driveability problem

CASE STUDY:
2006 Pontiac Solstice 

76,000 Miles 

2.4L DOHC EcoTec 

5-Speed Standard transmission 

“Intermittent MIL Illuminated/P0011” 

 The automotive technician of today is tasked with the everyday battle of finding solutions to the never-ending faults associated with the technological advancements of today’s automobile. While finding the answer to the problem is the ultimate goal, how you approach that goal is what sets the bar for an accomplished technician (as opposed to a technician who can barely get by). 

It's the ideological thought process that's key here. Approaching, and not attacking, the problem is the difference between success and failure. If you’ve ever had the chance to watch the training videos by my friend Bernie Thompson (of Automotive Test Solutions), you can see just how performing a logical approach to a problem will lead to a successful solution, rather than just going after the perceived culprit and taking that chance to miss your mark and sending your diagnostic process in the wrong direction. By doing that, you’ll not only have wasted valuable time, but it could cost you (or the shop) extra money as well. To avoid this scenario, two things need to happen. One is to get as much training as you can get. And the other is to completely understand the system that you are working on. 

Easy stuff first 

This is a case study that I did a while back on a 2006 Pontiac Solstice (Fig 1). This vehicle has a 2.4L Ecotec engine with a 5-speed manual transmission and 76,000 miles on the clock. The issue this vehicle was having is it keeps setting an intermittent DTC P0011.The code definition is “Intake camshaft position system performance.” Here is my first step in the diagnostic approach. The code definition is telling me that the performance of the intake camshaft is not what the ECM wants to see. There is something wrong with the position that the camshaft should be in. Think about these questions for a minute:  

-What factors can contribute to the intake camshaft being out of position? 

 -Is it a mechanical problem or an electrical problem?  

-Maybe it's a little of both?  

The other thing you have to remember is this is an intermittent problem. Understanding what the code definition means will put you on the right path to continue. Solving complex problems efficiently will only work if you gather data. Gathering data, analyzing it, and understanding it will be the next step in approaching the problem. 

However, looking at the data PIDs is not the next step yet. Looking at the code set status will give an even better clue (Fig 2). It can be seen that the code did not fail on this particular key-on event. But, since the last time the code was cleared, the code had set again. This means the PCM ran the test, and the test failed at one point or another. What it's telling you is while the code was set at one time through the drive cycle process, it did pass the last test. This should indicate that it is indeed an intermittent problem. This is a big piece of the puzzle that the technicians seem to miss as part of their diagnosis. There’s a lot of good useful data there that can aid in your diagnostic approach.  

There’s one more thing to look at before investing in any on-car testing, and that is viewing freeze frame data. Looking at freeze frame data can give you a lot of good clues (Fig 3). Right away, we can see that there are some useful clues. It shows the vehicle has been driven 164 miles since the last failure. The engine was at 2,500 rpm (not idling), and based on the coolant temperature reading, the engine was at operating temperature. Also, don't forget to acknowledge loop status, which tells you the PCM is minding the HO2 sensors for feedback. These are all good clues to aid in your approach.  

Now that we have some basic information, it's time I did some testing to look at some of the data using the scan tool. I like to call this driver’s seat diagnostics. Here you can perform some useful tests all while sitting in the driver’s seat. Most capable scan tools have bidirectional controls. We know that this vehicle was setting an intermittent code for an intake camshaft position performance problem but not a code for the exhaust camshaft. One thing I always like to do is test a known good component before I test a potentially bad component. That’s not to say that the known-good is indeed “good,” but chances are you will see what a normal reaction to your bidirectional test should look like.  

Driver’s seat diagnostics 

I set my scan tool to perform an active control test for the exhaust cam just to see what would be displayed and the reaction that the PCM will take. I activated the camshaft timing and noticed the changes that were made in each increment that I chose. Notice the data changes respectively (Fig 4). When looking at the data, notice that the actual commanded and the desired data matched with each movement of the scan tools command. What that’s telling me is whatever percentage that I tell the PCM to move, it’s following my commands. If I were to command it to 10% and it only moved to 5%, then that would tell me that there is either a mechanical issue going on or an electrical problem with either the component or the PCM not acknowledging the correct command. This exhaust camshaft is working like it should and therefore isn’t setting a DTC for a performance code.  

Now based on that test, I now know what to look for when I am checking the intake (suspect) camshaft. I performed the same bidirectional test to see what kind of response would occur. I started with a 5% command, and I saw that there wasn't any response to my command. Next, I set it at 15%; again, still no response. (Fig 5). At this point, it’s not yet known if the camshaft actuator is bad or is something else going on. But I do know something is wrong and further testing is required.  

Following the data 

So far in my diagnostic approach, I have gained some useful data. I know that I have an intermittent problem that only sets a DTC at random times. I know that based on my bidirectional testing that the intake actuator wasn't responding to the commands that were applied as the exhaust actuator did. At this point, you might be thinking that throwing an intake actuator will solve the problem and you can call it a day. But it’s prudent to know, will that truly fix the problem?  

Remember, since this is an intermittent DTC, that could crop up again. My motto is to test, not guess, so that's what I’m going to do. It's time to leave the driver's seat and do some on-car testing. I opened up the component tester in my scan tool and wanted to perform a few tests. I wanted to isolate the component from the rest of the system so I could make a logical and accurate decision on this vehicle.  

First, let’s get a little familiar with how a camshaft actuator works. CMP camshaft actuators use engine oil pressure to control intake and exhaust camshaft timing. On this vehicle, the solenoids are high-side-controlled by the PCM using a pulse-width-modulated signal. Cam timing is adjusted as the actuator is energized. Remember when I performed the actuator bidirectional control test and there wasn’t any change? I energized it by commanding it with the scan tool. Next, I want to test the actuator by performing a signature analysis.  

Setting my scope on the 20-volt scale and a sweep of fifty milliseconds, I was able to capture a fairly uniform waveform (Fig 6). Note this was at idle, and then toward the end of the waveform, I started to accelerate the engine. You can see where the signal got a little wider.  This capture is telling me that the command from the PCM is correct and present so I’m confident that this isn't a PCM or a wiring issue. Ok, now you might be thinking, “Let's just throw an intake actuator in it and be done with this problem.” As John Wayne would say, “Not so fast, cowboy.”  

There is one more test I would like to perform. I want to see if the cam actuator solenoid itself has any internal issues. My next test will be checking the resistance of the coil windings of the actuator. The specification for the actuator is 4.6-5.2 ohms. With the actuator unplugged and my test leads on both terminals of the actuator, you can see that this actuator is way over resistance spec (Fig 7).  

Now I am convinced that there is a problem with this actuator. I performed three different tests and gathered as much data as I could to make an accurate diagnosis. Based on experience, I knew this was probably an actuator issue all along. The reason for this case study is to prove to demonstrate that performing as many tests as I can and coming up with the same diagnosis is key to making an accurate diagnosis. Not only is it for accuracy, but it's also important for to keep my test skills finely tuned. 

Slow and steady wins the race

I mentioned earlier in this article that I wanted to show you what a diagnostic approach was. Having a clear understanding of the vehicle's system you're working on and gathering as much data as possible will further enhance your skills in testing. You will know what to test and why you're performing that test. This diagnostic without all the screenshots, documentation, pictures, and extra procedures in reality, took approximately thirty minutes. But spending thirty minutes and knowing that you have reached a successful conclusion is a small price to pay instead of guessing and possibly adding unnecessary parts and or labor to the job. Giving your customer a sound peace of mind as well as yourself the feeling of confidence will go a long way to enhance your reputation.