Remember that line from one of Clint Eastwood's movies? I do, and it rang through my memory again recently.

Last week, a friend of mine, (and former diesel mechanic), asked me if we could check out a check engine lamp problem on his Toyota 4-Runner. I told him to stop by and that we would give it a quick scan for codes. The scan reveled an OBD II code for a lean exhaust on bank one sensor number one. Being familiar with the Fuel Ratio sensor on Toyota's, I called the dealer to see if his vehicle was covered under a special warranty extension that Toyota had offered on this sensor. The dealer stated that his specific vehicle was not covered. I then advised my friend that technically, we should perform some checks to make sure it is the fuel ratio sensor first, although sensor failure is a common fault on some Toyotas. My friend decided to think about it and even stated that he may replace it himself.

About a month later my friend returned, asking if we could order the sensor and replace it. I stated that we could, and again cautioned him that it would be a trial item as we have not done any diagnostics to prove that the sensor is causing this fault code. My friend understood and agreed to take the chance on trying the sensor.  A week later we replaced the sensor and cleared the code. A few weeks went by and my friend was back again, this time with a coolant leak. This was quickly diagnosed as a leaking radiator and we got his authorization to replace it. In addition, he added that he also had a strange hesitation on take-off. A scan of the PCM did not reveal any codes this time. The IATN forum advised replacing the MAF sensor for a similar no-code hesitation. Luckily we had a similar vehicle in inventory, swapped over the MAF sensor and found that it did cure the hesitation. Again we obtained authorization for the cost and, later that day, my friend was on his way with the new MAF sensor and radiator.

A few weeks later, I again received a call from the 4-Runner's owner. Apparently the check engine lamp was back on. I again asked him to stop in for a scan of the PCM. Strangely enough, the lean exhaust code had returned. We ran a vacuum lean check with our smoke machine but were unable to find any leaks. However, our technician did notice that some mud had migrated over to the ‘filtered air' side of the air cleaner box and that this mud had also contaminated the new MAF sensor's sampling wire. We questioned the owner about this muddy air cleaner. The owner admitted to some off road use, but, not since we had replaced those parts. We cleaned the MAF wire and the air cleaner box and sent the customer on his way.

A few weeks later I again received a call from the customer. The check engine light was on again. I advised the customer to come in immediately for a PCM scan. Although I was not in the shop that day, the customer called me back later and seemed upset. Evidently, our technician had found that the lean exhaust code had set again. My brother then advised the customer that there was not much else we could do and that the car would have to go to the dealer. Understandably, the customer was upset. He asked me how we would compensate him for the money he had spent on this problem. I respectfully reminded the customer how he took the chance on replacing the Fuel Ratio Sensor and waived the methods and costs of diagnostics to make certain. The customer understood but felt that he had gotten a ‘bum deal'. I advised the customer that at times we can only as much testing as our equipment allows and that the dealer's Toyota Scan Tool can perform more comprehensive tests.

I told the customer not to worry and that we would work with him to get the problem resolved, even taking the car to the dealer for him if he so desired. The customer did call one of the dealers at one point, and upon hearing the code, he was told that it was still probably the Fuel Ratio Sensor.  I advised the customer that if the dealer found that our replacement sensor was faulty that we would provide a full refund.

All and all, it seems like independent shops are getting stuck and squeezed in the middle of a lot of these diagnostic dilemmas lately. We can only test and diagnose insomuch as the limitations of our scan tools and software. Problem is, you don't always find out what testing you're limited too until you have some time and parts, (read: money), invested into the car. It is extemely frustrating when this happens because your equipment's diagnostic limitations wind up making you and your shop look like fools. The only thing you can do is work with your customer to make them understand those limitations and then help them seek out an effective repair.