Over the past 35 years, I’ve witnessed a change in the way vehicles are repaired. The diagnostic approach or game plan in finding the cause of a vehicle’s problem has changed as well. For example, the strategy used for a 1982 Chevrolet Camaro in the shop for a “cranks, no start” complaint could be entirely different than it might be for a 2017 Chevrolet Camaro with the same complaint. Yes, you might start your diagnostic approach the same way by checking for spark or fuel, but with today’s vehicles and the increased use of electronics, sometimes it might be easier to start looking into the problem using a diagnostic scan tool first. With modern technology changing drastically over the course of the last 20+ years, your thought process needs to change as well. In this month’s article, as a mobile diagnostic technician, I’m going to highlight a couple of case studies that I solved using a diagnostic approach that works for me. You might find that these methods will work for you, or you might find that your own diagnostic approach could be completely different. It doesn’t matter which way is better. What matters is that whatever way you choose, you are able to find the solution to the problem that leads to fixing the vehicle.
Drama, drama, drama
When I get called to a shop about a vehicle that has a problem, it usually has what I call “drama” attached to it. The vehicle has probably been in the shop longer than it should have been, the technician working on the vehicle is probably frustrated and I’m sure his boss is as well. It is also probable that the vehicle has had more parts added to the ticket than my wife has shoes. Well maybe not that many, but the situation is not good and the frustration level is high. When I approach a diagnostic job I always try to keep two things in mind: keep it as simple as possible — meaning don’t over think or over analyze — and know the system you’re working on.
The first vehicle that I want to talk about is a 2006 Pontiac Solstice that has a 2.4L engine with 78,000 miles (Fig. 1). The vehicle came into the shop with a check engine light on, and it’s the second time back for this vehicle. This vehicle has a stored code of a P0011-00 for an intake camshaft system performance fault. This code is a “type A” code, meaning that after one failed drive cycle the light will be illuminated and a failure record will be stored.
Remember, knowing how the system works and reading the description of what the code actually means will make your diagnostic job much easier to solve. So after retrieving the code I looked at the description — “intake camshaft performance.” What that tells me is the performance of the intake camshaft is not good enough for the ECM to be happy. Think about it like a child day care center. If the child does not play nicely and follow the rules, then that child will get a time out. The ECM has a strict set of rules that have to be followed, and if the camshaft doesn’t follow those rules the ECM will illuminate the check engine light and put the camshaft in a “time out” — at a rest position. So, my next step in my diagnostic thought process would be to hook up my scan tool and look at the DTC status of this code (Fig. 2). The DTC status told me that this code did not run this ignition cycle, but it has failed since it was last cleared. The code did pass the last time the ECM ran the test for this code. So as of now this code is a history code and it did set the check engine light on. What does this tell me? That just clearing this code and sending the customer on their way did not fix this car. The shop did this on the customer’s first visit with the thinking that this was a history code and possibly a false code. Looking at the DTC status tells me that this vehicle has a problem.
This is a performance problem in the intake camshaft circuit so I want to test this circuit to see if the ECM is processing the signal properly or if the intake camshaft solenoid isn’t sending the correct information to the ECM. So let’s keep it simple. You have two components here — the ECM and the intake camshaft solenoid. Let’s isolate the two. When we start our testing process by disconnecting the connectors at the solenoid or ECM, we take the chance of disturbing the connections, which could be our problem. So let’s leave the circuit intact first. I hooked up my scan tool and wanted to look at the data that the ECM was looking at. As I looked at the scan data for the intake cam angle percentage, I watched the desired cam angle and compared it to the actual cam angle (Fig. 3). Throughout the rpm range, both the desired and actual specs matched. What that tells me is that right now the problem isn’t happening.
On this particular vehicle, I was able to perform a bi-directional test and command a change in the intake camshaft angle. I went into the test and was able to send a command to the ECM and watch whether the ECM acknowledged the change. Looking at the data PIDs as I altered the command Figs. 4, 5) showed me that the ECM did, in fact, see the signal sent but did not acknowledge a change. That tells me the ECM is at least awake. So is the ECM not able to make the change or is the camshaft solenoid not moving with the command sent?