This article contains a mixed bag of some common Asian diagnostic tips and techniques on a variety of vehicles. As you read through the different vehicle problems, you will learn what diagnostic route I rode to diagnosis and fix the concerns. In some of the different examples I will explain what I used to test and confirm that a component was either good or bad. Never just change a part; but rather test it, then move on to the next logical step in your diagnostic routine. And use what God gave us—our brain, eyes, ears, nose and hands. Combine that with good service information and you will have a successful diagnosis.
|Want more ? Enjoy a free subscription to Motor Age magazine to get the latest news in service repair. Click here to start you subscription today.|
Toyota Camry P0171
One of the most common vehicles that shows up in our bays is the Toyota Camry. A common problem that this vehicle will display is an illuminated Malfunction Indicator Lamp (MIL) caused many times by a P0171 (System Lean-Bank 1) Diagnostic Trouble Code (DTC). As part of my usual diagnostic routine, I first performed a visual inspection and on this particular Camry. I noticed that the Mass Airflow sensor (MAF) and Air Fuel Ratio sensor (AFS) had been replaced. Seeing a bunch of new parts on a vehicle that other shops have installed without resolving the problem is nothing new to me. Before replacing any sensor or actuator, the first thing to do is "test and not guess,” confirming that the components are operating in the proper range or not.
The important thing to know about the Toyota AFS sensor is at idle on a good running engine, the voltage reading on your scan tool should be 3.3 volts. To check the sensor, induce a vacuum leak to see if the sensor reading changes from the idle voltage reading. If the voltage reading goes up with an induced vacuum leak, the sensor is able to correctly read a lean condition. To check to see if the sensor is capable of reading a rich condition, add some propane to a vacuum port while making sure the voltage goes below 3.3 volts. Since the sensor tested good on both lean and rich conditions I moved on to testing the MAF sensor.
To perform an MAF sensor test I like to use the EScan scan tool that makes testing the sensor easy. The scan tool has a Sharp Shooter tab that incorporates an easy test feature to test Volumetric Efficiency (VE). In order to perform this test properly all you have to do is input the correct engine size, temperature and elevation. Once the correct information has been typed in, drive the vehicle while depressing the throttle pedal to Wide Open Throttle (WOT) a few times. (Note: Perform this test from a rolling start in first gear, followed by a WOT acceleration through the second gear upshift. Do this in a safe section of road near your shop and always obey local traffic laws in the process.) The tool will display the results based on what the VE table calculations test results currently are compared to the actual results. This is a very accurate and time saving test that allows me to confirm if I have an induction problem. Problems could be related to a clogged air filter, intake manifold, valve problem including carbon build up and even a clogged exhaust. The tool will graph two lines; the red line is based off the engine size, temperature and evaluation while the yellow line displays the test results. The example (Figure 1) displays a lower than acceptable reading along with turbulence on the yellow graph, indicating a clogged exhaust. If the test results were normal the yellow line would be over the red line, indicating that the intake system was good.
Now if you don’t have this tool, don’t worry. You can perform a similar test, though not as accurate, by using any Generic/Global OBD II that graphs. Select the Calculated Load Parameter Identifier (PID) from the list and graph it. Once the selection is setup, start the engine and take the vehicle out for a test drive. You will need some clear space so you can depress the throttle pedal to it’s WOT limits a few times. For safety reasons, make sure you are in a safe area and that someone else is driving while you are operating and viewing the scan tool test results. After achieving WOT a few times, it’s time to view the graphed results of Calculated Load (Figure 2), making sure the graph obtained at least 90 percent at WOT.
Our problem Camry had passed both tests so I decided to dig a little deeper and do more research. I had completed my visual inspection, scan tool query and checked for Technical Service Bulletins (TSBs), but found nothing that provided information for my P0171. My next step was to check Identifix and iATN to see if there is any information that could assist me in solving this problem. Bingo! Identifix had some good information on the most common problems reported on the 2007 Toyota Camry. It reported the abnormal brake pedal feeling that I had experienced on one of my test drives. The Identifix information stated that sometimes there is a symptom of a hard or harder than normal brake pedal that is caused by a ruptured diaphragm in the brake power booster. The scan tool data on Long Term Fuel Trim in Freeze Frame was at +7, indicating that there was a problem that can be from many different sources. I have come across some Toyotas that had a P0171 due to intake gasket problems, but the DTC usually sets when the engine temperature is cold. The Freeze Frame data indicated that the DTC on this vehicle occurred when the engine was at operating temperature so that ruled that problem out.
Since I already had the EScan connected to this vehicle, I thought that I would check the fuel trim at idle while I depressed the brake pedal as suggested in Identifix. On the EScan, there is a separate test for fuel trim that is located in the Sharp Shooter tab section (Figure 3 & 4) that would allow me to view live results in either Short Term Fuel Trim (STFT) or Long Term Fuel Trim (LTFT) as I depressed the brake pedal. As you can see from the test results on the tool, STFT at idle was high while I was depressing the brake pedal and good when my foot was off the pedal. This vehicle was diagnosed and repaired quickly with a little help from my friends at Identifix and with the replacement of the brake power booster.