Scope & Scan - Service Repair

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Just another day diagnosing troublesome vehicles

Every day in the shop presents new challenges – some easy, some not so much
Wednesday, December 31, 2014 - 09:00
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First on the list is a 2003 Toyota Highlander 3.0L V6 that came in with a few Diagnostic Trouble Codes (DTCs): P0420 Catalyst Efficiency Below Threshold Bank 1, P0441 EVAP Emissions Control System Incorrect Purge Flow, P0442 EVAP Emissions Control System Leak Detected – Small Leak and P0446 EVAP Emissions Control System Vent Control Circuit. So where do you start when you have these many DTCs?

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Our first step was to take a look at Freeze Frame data to check out when it happened. Freeze Frame data usually provides us with good information such as engine temperature, vehicle speed, throttle position, fuel trim data and more. On our problem Toyota, Freeze Frame data was helpful only in providing information on the P0420 DTC since this code has priority over the others. Because it potentially was the most expensive fix, we decided to start with it first.

As general practice, our next step was to do a little homework before we started working on the car. We always look for related Technical Service Bulletins (TSBs) and poke around in a variety of online resources like Identifix, iATN and even Google to make sure we don’t miss anything that may be related to our problems. Information is always a good place to start especially if you’re not 100 percent familiar with the system. When working on so many different vehicles, it becomes difficult to know every system inside and out. The easy stuff to remember is that the purge valve normally is closed and the vent valve normally is open, but not knowing where they are located or what they look like can make your diagnosis difficult. In this case, Toyota labeled the purge and the vent with different names, making it more confusing. So reading up on the system before you dive into it is a real good idea, because it provides you with a better understanding on how the system fails and sets a DTC. This vehicle had more than 100,000 miles on it, was well maintained and all of the service work that had been performed was documented in the owner’s logbook.

The good news for the vehicle owner was that we were able to restore the cat’s function with a good fuel system cleaning and were successful in extinguishing the P0420, but the bad news was that there were still three EVAP DTCs to diagnosis.

With any DTC, it’s a good idea to read the code setting criteria carefully in order to move in the right direction. Look for something in common when diagnosing multiple DTCs. Don’t just replace parts when a DTC appears, since it’s not always a bad part that is causing the problem. On this vehicle, I found the EVAP problem while I performed my visual inspection. Take a look at Figure 1 to see what I found.

My visual inspection fixed all three of the DTCs with one simple connection. You should have noticed that there is a metal tube next to the air cleaner box that is missing a vacuum hose. Sometimes it the simplest things that fix a vehicle, always use a thorough visual inspection as part of your diagnostic game plan. Curious how the hose wound up being off the tube? After reading the owner’s logbook, I found out that the vehicle was taken in for a quickie oil change where he was also sold a new air filter. Most likely the oil change tech was in a rush as he pulled off the air cleaner housing and the vacuum line from the air box came off. If you are not paying attention to details, problems such as the one we described will occur.

Under Water
The owner of a 1999 Porsche Boxster with 36,230 miles brought his vehicle in with a complaint of sticking brakes, stating that it felt like the brakes were staying on even after he removed his foot from the pedal. After a complete inspection of the brake system, we found that the front brakes were the cause of the complaint. The front brake calipers were sticking, causing the brake pads to wear along with discoloring the front rotors. Our findings seemed straightforward; it just needed a front brake job, so we suggested replacement of the front pads, rotors, calipers and a flushing of the brake system.

The Boxster owner gave us the approval, so we ordered all the Porsche brake parts, including nice, new, black-painted Porsche caliper(s). After we installed all the new parts, flushed the system out and road tested the vehicle, we were confident that we had addressed the owner’s concerns. After we complete any brake job, we want to make sure that the vehicle rolls easy confirming that the brake are not holding on. There is nothing worse than completing a brake job and having the owner come back with a brake complaint. To make sure that the brakes are working properly we perform one last test making sure that the vehicle can roll on a flat and slight incline surface with a slight push. Since everything checked out OK, this Porsche was ready to return to the owner.

Well that old saying, “It’s not over until it’s over,” was true on this vehicle. This vehicle would come back to haunt us with the same complaint, and I think you’ll agree the cause the second time around was one that would have had any tech scratching their head in disbelief. Here’s what happened.

We had a very dry summer in the Northeast followed by periods of heavy rain. A few days after the storms, the owner noticed the brake problem. He called asking if he can bring the Porsche in because he felt that the brakes were sticking again. When the vehicle arrived at the shop, we checked the complete brake system and found no signs of overheated rotors or sticking brakes. When we completed the brake inspection, we performed the roll test again and found that this time, it did not roll so easy. We did notice a strange noise that seemed to be coming from the brake pedal and firewall. The noise was a swishing and squeaking sound that was real weird! We looked at the brake pedal connection to the master cylinder under the dash and sprayed some penetrating oil on it but there was no change.

We decided to lift up the hood and remove the cowl to check the master cylinder rod to the power booster connection and found the answer to our problem. We found under water up to the top seam that covered the brake rod going into the power booster. Take a look at what we found in Figure 3. The drain tube located at the left front fender well was clogged, allowing water to build up in the cowl and find its way into the power booster and master cylinder. Every time the brake pedal was depressed, water was being compressed in the power booster causing the brakes to not fully release. Cleaning out the drain tube and replacing the damaged parts was all we needed to do to get this Porsche back to normal.

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