Fuel trim Issue 2005 Chevrolet Colorado

A few years ago a fellow showed up with a 2005 Chevrolet Colorado with a 4.2l 6cyl. It had a misfire at idle that was proven to be valve seat failure which was common for those engines. We didn’t get to do the repair because of a special policy set up by the manufacturer.

Just this past week the customer came back to us after numerous attempts at other shops to have a check engine light issue repaired. The vehicle couldn’t even have its emissions test run because of two incomplete monitors, the catalyst and the evaporative emissions systems.

When dealing with one of these the first step is to retrieve and write down any codes, check and capture freeze frame and failure record data and then get a good road test in so that you have a good baseline on how the emissions system on the car is functioning.

There was a P0171 set in the computer’s memory, that’s a lean air/fuel ratio code. Checking the freeze frame the code set at 25% engine load and 33 mph, that’s a light throttle condition. Now the question that has to be asked yet is whether this is the only time that the engine is too lean or not. The answer to that is easy, start the engine and get the truck into closed loop. Check the fuel trims at idle, no load and what I saw was the long term trim at +25%, and the short term trim +20%, that’s a total correction of 45% which is a very lean condition. The next step is to try and determine if this is a vacuum leak or some other fuel issue. To do that the engine speed is increased to 2500 rpm while again monitoring the fuel trims. They were still +25% long term and +20% short term just like the no load idle. Generally if the problem is a vacuum leak there will be a smaller correction at the higher speed because there is less time for the leak to impact the air/fuel ratio. The next step is to put the car into gear against the brakes and speed the engine up to around 1500rpm. Now there is almost no manifold vacuum, and a vacuum leak would be nullified if that was the cause of the problem.  The trims were still a total correction in the 40% range.

This is information that is gathered before the car ever moved from the spot the customer parked it at. Think about what the next step should be, and what the possible causes are. I’ll post the next part of this vehicle in a few days.

Just good people who do a difficult job

A couple years ago NBC news, Jeff Rossen, did a "sting" on auto repair shops using a defective AC relay. Like most of those attempts they found some things that really are bad about the repair trade. The caught some dishonest people and most techs want nothing more than to have people like that out of our trade. At the same time they also found things that are actually bad that they praised!. In the end they really only succeeded in exposing some people who were giving all shops and techs a bad name, but did nothing about the underlying causes for the behavior.

I've made it a point to be a thorn in the side of one of the groups that participated in that sting. They are portrayed as experts and sat in judgment of shops and techs and routinely were giving advice to consumers that was flat out wrong. I always made it clear why I was there, but the individuals who were involved in the sting refused to subject themselves directly to my scrutiny. That was a wise move on their part, they really didn't have anything to gain,  and besides they didn't have the expertise at auto repair that they claimed and I would have made that very evident.

Well this week Jeff Rossen came out with this "sting". It speaks for itself and while not perfect its good enough and for my part I'll steal a line from Harry Potter. Mischief Managed. Maybe the pressure that I brought had something to do with this, maybe it didn't. But it's about time the public gets to see real techs doing what they do everyday, and that's their best to try and take care of their customers.

http://www.today.com/news/could-little-dashboard-light-cost-you-big-bucks-2D11603387

I could ony advise the techs to find new jobs as fast as they could.

Another technician wrote a post about a dealership who has restructured their service department so that they have some techs who only do diagnostics, and then they pass the cars onto other techs to do the actual repair. The real kicker is that they take two productive hours off of the regular techs each day to make a pool from which to pay the diagnostic techs. I can only wonder how people who know so little about being a technician get into a management position over them where they get to make these kinds of decisions.

 

I could see myself as potentially one of the diagnostic guys. What I can't see is handing the work off to someone else once the diagnostics are completed. Fixing the car means also doing the actual repair  because that serves to reinforce the intuitive side of a technicians knowledge and experience. As one of the other posters noted anytime the process doesn't work and a car isn't repaired, who do you point the finger at? IMO, the moment you have to start pointing fingers you have all the proof that you needed to prove that this wasn't a good idea to start with.

 

Getting good at diagnostics requires just plain getting good at fixing cars, plus a whole lot of hard work on top of that studying and developing as Jim Garrido says a good game plan. I think most of the top techs will agree with me that there were a lot of mistakes on the way to figuring out their game plans, and most of the lessons taught by those mistakes were (and occasionally still are) learned the hard way. One of the toughest hurdles was to learn to take a patient disciplined approach, especially when the store only wants to pay pennies no matter how much time needed to be spent doing diagnostics. I have 1999 Jaguar XK8 in the shop right now that makes for a good analog.

 

A week ago a shop sent it to me for a P1646 which his information showed to be fuel pump #2 relay control circuit issue. Except that the #2 pump is only used on the super charged cars, so right away he had no idea what was going on with this car. It took some researching and it turned out that P1646 is for the heater circuit upstream sensor bank A. But instead of having me go through the steps to prove what the failure was and complete the repair the shop stopped the diagnostics and took it back to their place to just throw a sensor in it. In the process of doing that they bought a "very inexpensive one" compared to the O.E. that I would have recommended and to install it they had to splice the connector from the original sensor. Two key starts later, the light was back on and the code had reset, so now they wanted it tested completely.

 

If you are able to look at that paragraph and see quite a few miss-steps, from not fully diagnosing the problem at any time, to them having inadequate service information, and then using questionable parts and repair habits you see how a lot of shops run. By the numbers, however 95% of the time they were going to get the final outcome correct by just slamming that sensor if they had only used a quality part so one can argue there is a potential reward for that approach. However instead of fixing the car, they added yet another variable to the problem and that has both of us further away from fixing the car than they were a week ago. At least they broke tradition at this point and are going to let me prove what is going on before they just slam another O2 sensor even if it is the correct part this time.

 

The real problem isn't whether what that dealer is trying to do is legal or not, it's how many things will go wrong with it because management hasn't thought it out completely.

The above scenario where some techs are doing the diagnostics and while others are replacing the parts are going to create a lot of Jaguars, and when they slam the parts and get it right they will turn around and feel that the lower level tech was all they needed. While if they still rush it at all they will defeat the whole idea of having the diagnostic techs in the first place and that's when the finger pointing will start. One of the worst parts of this is they have just added a glass ceiling to the career path for the next generation of techs who should be learning to be their diagnostic techs of the future, and they are taking two hours off of them each day  to pay for all of this. To me that shows that they don't care about technician retention nor does the management understand the long term technician career path.