Evaporative Emission System P0496

2012 Buick Enclave 3.6 engine, MIL on, stored P0496, "runs bad at times" complaint. 

With the complaint of the malfunction indicator lamp (MIL, Check Engine Lamp) on, checking for stored trouble codes is the place to start. Today we'll be using the OTC Encore for the initial check. The tool was just updated and I want to see how it performs with the updates. My main complaint with the Encore in the past has been system speed. The system seems to be much faster now. On with the show!

We have a pretty solid P0496 stored which is described as EVAP system flow during non-purge. 

The longer description contains the reason for the failure code. The engine computer closed the vent valve and the purge valve and saw (fuel tank pressure sensor) vacuum being pulled on the tank. There should have been no vacuum. 

Evaporated fuel vapors are stored until the purge solenoid opens. When the solenoid opens then vacuum draws the vapors into the engine where it becomes part of the fuel mix. Open at all times is going to upset the fuel mix and cause some driveability problems under particular conditions. "Runs bad at times". I removed the engine cover to access the purge solenoid for testing. 

Scan tools these days often have databases of common problems. "Code Assist" is available on the Encore. The most common fix for this code is to replace the purge solenoid. That doesn't mean it is bad, replace it. It means that it would be a good idea to start your tests there since it is the most common failure. 

That reminds me, the Encore is also internet friendly. If I wasn't familiar with testing the purge solenoid or with the system I could do deeper digging from within the scan tool without traveling back to the desk computer. Identifix is a good place to take a step further from where we are right now. Since the solenoid is normally closed, disconnecting the wiring and will eliminate an electrical problem. 

I used the vacuum gauge so you could see there is engine vacuum at the port when there shouldn't be. 

After that it is time to go online to the desk pc, enter the car, find the part I want and order. Kinda like getting pizza. 

Always compare the new part to the old.

Also test your new part to be sure it isn't stuck open as well. Always remember NEW doesn't mean GOOD. It just means new. 

Everything worked and I put the engine cover back in place. Time to clear engine codes but first we want to look at the data for misfires. The car is approaching 80,000 miles. The spark plugs are reaching the end of their life with a recommended replacement at 97,500 miles. If I see any misfire history I'm going to do a spark plug inspection. If we clear the computer we'll lose the misfire history. 

Nothing to see here. Looks like we need to clear codes, do some monitor friendly driving and check for any new codes. 

As always, thanks for reading!!

Kenneth Hayes

G&G Auto Repair

Searcy Ar. 

Rough Running Chevy or How Can It Be Missing When It Is Sitting Right There?

A misfire. A cylinder that is not contributing to the engine running is said to be misfiring. I remember that when I first started doing car repair that determining a misfire vs poor running took a very long time to learn. Oh I could tell when an engine was running bad, but that isn't necessarily a misfire. It gets even more complicated, there are varying degrees of misfires. There are different types of misfires. There are different conditions and causes of misfires. All these years later though and I can tell a misfire on a car just driving past the shop on the road out front. I could also tell I had an ignition misfire on the 2010 Silverado that I just drove into the shop.
The customer had said it might be a misfire, or just a rough running engine. Just as I said, it can be hard to say one or the other without some experience. When he added that the check engine light was on and sometimes flashing well that clinched it. Since OBDII was born (second generation on-board diagnostics) automobiles are required to have a flashing check engine light to alert that the engine is misfiring badly enough to damage a catalytic convertor.
The slight intermittent miss I felt under light load coming into the shop is pretty typical of a secondary ignition misfire. Secondary ignition is the spark output to the spark plugs. The problem areas there are coils, spark plug wires and spark plugs. I suspected I would need plugs and plug wires. Problems with either goes hand in hand.
Remember, diagnostics is taking a broad range of possibilities and narrowing that down to the actual problem. I had taken "misfire/rough running" to "intermittent secondary ignition misfire", at least in my own mind. Therein lies the next step. I know that I have a pretty good idea that there is a bad plug or bad wire or both but I do need to go further before just throwing parts at it. I have an 8 cylinder engine here but a misfire on only one cylinder. To test further I need to find out which cylinder is misfiring. Testing secondary ignition on cylinders that have no misfire isn't going to be helpful and is a waste of time. Since the misfire is intermittent it isn't as straightforward as looking for a misfire that is always present but it isn't difficult either on this vehicle.
Years ago this would require might putting an assistant inside to create the misfire and me under the hood disabling cylinders until I found the one with the problem. Thankfully it is pretty rare to have to do that these days. Since the misfire was bad enough to flash the light, then I should have a misfire code stored related to the cylinder causing the problem. P0301 is a misfire code for cylinder one, P0302 is cylinder two and so on. Let's take a look at stored codes:

That was a lot less helpful than I had imagined. P0300 is the equivalent of what the customer told me in the first place. It might be a misfire or it might be a rough running engine. No need to surrender and look for an assistant yet though. This truck has the GM datastream items to allow you to see stored misfire histories and even current misfires (live). We'll look there next. 

Looks like we should home in on #7 cylinder. It even racked up a first misfires for me when I started the engine and gave is a slight load. I want to say here that there is NOTHING about a a misfire code that means anything more than the computer on your vehicle has detected a misfire. There is nothing about that code that means you need spark plugs or injectors or valves or anything other than you have a misfire. You may need any, all or none of those things. You have to determine what the problem is for yourself. Now lets look at that #7 spark plug.

Time for spark plug replacement. The engine is burning some oil causing the carbon buildup. 

Thanks again for reading!

Kenneth Hayes

G&G Auto Repair

Help! (or, Can You Assist Please My Car Won't Start)

The complaint was the car stalled on a trip and would not restart. The car was towed over the weekend and setting in the lot to welcome me on Monday morning. I gave it a quick look to see that it was safe to try and crank the engine. It is always better to see that half the engine isn't taken apart or similar while others before you were trying to get the car running. It looked safe to try and crank the engine.
Let me take a moment here to make note of "will not start" complaints. In diagnosing a problem what you are really doing is narrowing the possibilities down to the actual cause. When I turned the key to start position there was no starter engagement. The complaint just went from "will not start" to "will not crank". Engine *cranking* is the starter engaging and turning the engine. Focus was now on why would the engine not crank.
Clues were that the instrument cluster lights were flickering, gauges were erratic and no headlight operation when the light switch was turned on. Those things could be from a discharged battery. If you are not familiar with a "booster pack" it is a sort of portable battery with attached cables. You can connect the cables directly to the car and power the electrical system with a "known good" battery without a lot of trouble. 

With the booster pack connected the lights work, the gauges work, the door chime and interior lights come on AND the engine will crank. The engine will also start and run. The diagnostic problem had just shifted again. I was now looking for why the battery was dead. The next clue was the battery light on the instrument cluster. The red battery light was on with the engine running.  A battery light usually indicates an alternator that isn't working. I checked the system voltage at the booster with a voltmeter and since the voltage was the same with the engine running as it was when not running it also indicated an alternator that wasn't working. 

Ideally I wanted a fully charged battery before doing some charging system tests but the battery was not accepting a charge after quite some time on the charger. The actual battery on this car is inside the fender on the driver's side. It is not readily accessible. I could attach the booster pack and do some charging system checks using that as a battery. An extremely discharged battery can take an overnight on the charger to reach full charge and this one looked like it was going to do just that. I could see through to the battery from the engine compartment and the battery looked new, with good clean connections. I decided to go ahead and test the charging system using booster pack as the power source. 

Since I wasn't seeing charging from the alternator I started by testing for voltage at the alternator. I had power at the output post (large wire). There is a connector with 2 small wires at the alternator. The brown w/gray stripe should have power when the car is running and the computer is trying to energize the field circuit. I had power there as well. The alternator should have been charging, but wasn't. I needed to let the battery charge overnight and get an okay from the car owner to replace the alternator. 

The problem went from no-start to bad alternator step by diagnostic step. 

Thanks for reading!

Kenneth Hayes

G&G Auto Repair