Issue: Check engine light on with a P0442 fault code
Vehicle: 2006 Saturn Vue, 2.2L
Tools used:
- Scan tool
- Vehicle repair information
- Diagnostic smoke machine
- DMM
- Power Probe
Arguably evaporative system (EVAP) issues are some of the most common, and quite often, some of the more difficult problems to diagnose.
There are really two main topics of fuel evaporative system diagnosis. The first, and more common, is fault code analysis. We’ll review how to diagnose a fault code analysis in this Tool Briefing.
The second, and one that at times can be extremely frustrating, is getting the EVAP monitor to complete. If you do not perform emission inspections, an incomplete monitor may not seem that important. But as we will discuss, this monitor can provide a window into other issues within the engine management system. We’ll cover this topic in a future Tool Briefing article.
Starting the fault code diagnosis
I have spoken with several experts in the EVAP tool industry and they agree the number-one call into their tool support hotlines is that technicians cannot find a leak in the EVAP system, but there is a code that indicates a leak is present.
After many years as a technician and shop owner I have learned two things:
- Things are not always as simple as they seem.
- Things are not always as difficult as they seem.
When it comes to fault code diagnosis on OBD-II vehicles, the first step is one that is often overlooked or dismissed as unnecessary. This simple step is to verify there is actually a problem with the system, as the presence of the code suggests.
Well, that sounds both frustrating and somewhat familiar, but remember, our first responsibility as technicians is to duplicate the issue.
Let’s talk about the likely cause of a leak code where no leak is currently detected. In many cases, the vehicle may have been fueled and the driver did not tighten the fuel cap completely. Most likely, a leak code will be set. Typically, before the vehicle reaches your shop for diagnosis, the cap is either tightened, or the vehicle has been fueled again and the cap is installed correctly once the “check light” has been triggered.
In either case, the leak has been repaired and depending on how, and how long, the vehicle has been driven, the light may either still be on or has turned off, but the vehicle will still have a history code.
Step 1: Retrieve fault codes
The diagnosis of the vehicle starts with obtaining any codes that are present -- either current, history or pending. Along with any codes, your scan tool has the ability to get quite a bit of valuable information to use in your diagnosis. Collecting the freeze frame information will provide you with the exact details the vehicle was operating under when the code set. This is useful during your diagnostic test process and after you repair the system. If you know the exact conditions that were present when the code set, you are able to operate the vehicle in the same manner to verify the code does not return after the repair.
Additional information can be found in Mode $06. You need to remember that Mode $06 is a function of generic OBD-II and depending on your scan tool, you may need to access it from the generic mode, not vehicle-specific enhanced mode of your tool. Many technicians see no real value in Mode $06 other than to find which cylinder is misfiring on some vehicles. Once you understand what Mode $06 is and does, you will see the value in adding it as part of your normal diagnostic process.
The monitor status of the non-continuous monitors reported in Mode $06 are from the last time the monitor was run, or completed. An incomplete monitor means the conditions were present to start the process, but something occurred to stop it prior to being fully completed.
Monitors that run the required number of successful pass tests will turn the “check engine” light off and eventually erase the fault code.
On our Saturn, the monitor was complete and had failed the small leak portion of the test. But remember, those results were from the last time the monitor had completed.
Step 2: Obtain vehicle specific system information
A key component of information gathering, especially in reference to EVAP issues, is to ask the customer if they have either tightened the fuel cap or filled the tank since the light illuminated. This customer said they had done neither.
The next step is to retrieve any codes. After obtaining codes, many technicians will start by following the diagnostic fault tree steps to diagnose the code. Other technicians will rely on their years of experience by testing the system to determine where the leak is, or try tightening the cap to find out if it is loose.
Quite frankly, neither method is exactly right, or wrong, and will probably not work on every vehicle, nor every code. The tried and true way to determine the cause of any failure is to use your repair information source to find out how the system works specific to that vehicle and to determine what conditions will cause the code you are diagnosing to set.
In the case of our Saturn, we used Mitchell 1 Pro Demand to first read the system description, which explains how the system operates and what the diagnostic monitor determines to be a fault. Next, we read the explanation of the fault code itself and the conditions for setting the DTC.
Having knowledge of the system, along with a complete understanding of how the system determines if there is a fault, can help guide you through a complete series of tests to find the root cause of the issue.
Step 3: Duplicate the concern
When duplicating the concern, you can jump right in by using your smoke tester to check for leaks. In the best case this is premature, in the worst case there is not a current leak and this is a complete waste of time. Armed with the details of what conditions need to be present to set the DTC, we can see if there are any conditions currently existing that will prohibit the monitor from running.
We found by researching the system, the fuel level needs to be between 15 percent to 85 percent, and the coolant and intake air (ambient, or outside air) temperatures need to between 39 degrees F and 86 degrees F at engine start-up for the monitor to run. The day we tested this vehicle there was an overnight low of 91 degrees F, which means one of the conditions for running the monitor was not met, and therefore, the vehicle cannot run the monitor to test the system to determine whether it will pass or fail. What this tells us is the fail results indicated in Mode $06 may not reflect the current condition of this vehicle.
If the EVAP system monitor had run and passed, we could assume either the system is now functioning correctly, or there is an intermittent problem. Since it had not run, we cannot be certain there is a leak in the system.
Step 4: Test the system
Because there was not enough information in Mode $06 to verify the presence of a current leak, the next step is to use your scan tool’s bi-directional controls to test the system. On this particular vehicle and with our scan tool, we have the ability to perform a “service bay test,” which performs a complete test of the EVAP system to determine if it will pass or fail. Our experience suggests we should perform this test at least three times to catch any intermittent issues. On this vehicle, it failed the second test, confirming there was an intermittent leak.
In order to fully test the system, use your scan tool to monitor the oxygen sensors. When the purge valve opens, there will be an increase in voltage on the upstream oxygen sensor(s). Depending on the level of fuel in the tank and whether it has a return or returnless type of fuel delivery system, the voltage increase can be significant, or relatively small. This is due to the amount of vapor stored in the canister and then purged into the intake changes with varying conditions.
After verifying there is flow and that the flow stops when you de-energize the purge valve, you can move on to using your smoke machine to test the system.
On many vehicles, you can install your smoke tester directly to the service port located on an EVAP hose under the hood. The potential issue with this is you will not be able to determine if the service port is the source of the leak. To eliminate this possibility, insert your smoke tester at a different location in the system.
Once the smoke tester is installed you may need to calibrate the flow meter by following the tool manufacturer’s instructions. Once that is done, apply smoke to the system and note the ball in the flow meter. If the ball is moving from its “no flow” position, there is a leak. The flow meter will provide an indication of how large the leak is.
If the flow meter is indicating a leak, start looking for a smoke trail. This sounds easy, and in many cases, it is. Sometimes though, the leak may be located in hard-to-see areas like on the top of the fuel tank or inside body panels. Another thing that may make it difficult to locate a leak is most shops are brightly lit, and you may not easily see a smoke trail, especially if it is a small leak.
One trick many technicians try is to increase the amount of pressure on the smoke tester, which may make it difficult to pinpoint or even seal the leak. One trick that may work is to dim the lights in the shop and use a laser pointer along the EVAP lines, which will highlight the smoke trail.
When we connected the smoke tester to the Saturn there was no flow on the flow meter, indicating there was currently not a leak in the system. We could have stopped there because we were not able to duplicate the issue, but in our experience, there are some things that can cause intermittent leaks and we wanted to test those items.
Two fairly common issues are either the vent or purge solenoids intermittently sticking. Remember, vent solenoids are normally open and purge solenoids are normally closed, so you will need to apply power to a vent solenoid to test it for a leak, and remove power to test a purge solenoid.
It is a good idea to use your DMM at the connectors of both the vent and purge to check for system voltage when the solenoids are energized. Also compare the resistance of the solenoids to the specifications obtained from your repair source. We tested both solenoids and found readings within the listed specifications.
The best way to catch an intermittent solenoid leak is to connect your smoke tester directly to the solenoid while you use either your scan tool or a Power Probe tool to energize and de-energize the solenoid as you look for smoke leaking from the outlet. Another way to test these solenoids is to apply smoke and see if smoke flows when you tap lightly on it while it is in its closed position.
We removed both solenoids from the Saturn and tested them on the bench. We found no issues with the vent solenoid, but the purge solenoid intermittently leaked when we tapped on it. We replaced the solenoid, then performed the service bay test on the system four times, all of which were successful.
This vehicle’s issue reaffirmed that performing a leak check on every vehicle that comes in with an EVAP code is not necessary. It also confirmed that following a good diagnostic strategy, starting with making sure there is a problem with the system and verifying you have corrected it, is the best way to handle any issue, especially intermittent ones.