A shop owner called me one day frantic about a 1999 Ford F150 pickup truck with 78,820 miles that he could not get rid of a P0401 EGR code. I arrived at the shop to see a very clean low mileage Ford truck with a 4.6 liter. Lifting up the hood I could see a new EGR valve, a new EVR (EGR solenoid), a new DPFE (Delta pressure feedback egr) sensor, a new exhaust tube for the EGR, and new DPFE hoses. Some parts the shop put on and others the customer installed. I quickly ran a KOEO (Key on engine off) test there was a P0401 (EGR low flow) code in KAM. No on demand codes. I moved on to the KOER (Key on engine running) test but first I hooked up an old fashioned vacuum gauge on the vacuum hose between the EVR and EGR valve. When you run a KOER test the PCM will activate certain outputs such as EGR and look for change. I was interested in if there was any vacuum going to the EGR valve during the test. During the test I indeed saw vacuum going to the EGR valve. The control side of the EGR system seemed to be in order. The test completed and a P0401 was set in KOER. Next step was to actually put vacuum to the EGR valve at an idle and see if it caused the engine to run rough indicating the EGR was opening and that the exhaust and intake passages for EGR were not clogged. Putting vacuum to the EGR valve didn't cause the engine to change at all. I could physically see the EGR valve diaphragm opening. I unbolted the EGR valve and started the motor the intake port were completely clogged. No vacuum could be felt. Considering the low mileage and the common issues with this issue I instructed the shop to remove the throttle body so I could show him the clogged ports. 10 minutes later the throttle body was off and sure enough the ports were clogged solid. Leaving the shop I gave the shop owner a quick rundown of how the system works and how it tests itself to see if it fully functioning.
A couple of days later I get a call from the shop owner saying he gave the vehicle back to the customer and the MIL (Malfunction illumination lamp) came back on and it has a P0401 again! Huh? This was a slam dunk diagnosis. I asked the shop owner if he ran a KOEO/KOER tests before releasing it to the customer. His reply was "I scanned it". I also asked him if he put vacuum to the EGR valve did the motor run rough or stall? Again, I got a reply "I think so". I told the shop owner I would stop by later in the day. Those that know me already know that this vehicle would be gnawing at me all day until I got there. I take things very personal. Did he clean the passages completely? Did another issue crop up?
I arrive at the shop and first thing I do is apply vacuum to the EGR valve and the engine ran very rough almost to a stall. Well, he has the passages clean now. Now, lets retest to see if it still is getting vacuum to the EGR during a KOER test. It was. Ok, does the PCM actually know the EGR is opening and flowing. How the PCM knows this is from the DPFE sensor. It senses flow across a controlled orifice in the EGR tube via those two brand new hoses. I hooked up my scantool and graphed the DPFE voltage. On a plastic DPFE such as this one KOER with no EGR flow you should be at 1.00 volt as EGR flow increases so does the voltage. I normally can get upwards of close to 4.0 volts or more when adding vacuum to the EGR valve.
Totally different story here.
We are flowing now. The DPFE hoses have a large and small opening and have to be orientated correctly at the EGR pipe and the DPFE. Somehow, someone managed to mix these up. You really have to try really hard to mix this up. Now, were these hoses like this on my first visit? I really can't say for sure. I didn't check-shame on me. I was so caught up on diagnosing the clogged passage I didn't see if the hoses were orientated correctly. To be honest this is the first time I have ever seen this. However, I won't be making this mistake ever again. I ran a KOER test and all was well.
Some details you don't see on the scantool. Some you have to see or feel.
Here is a 1999 Ford Expedition with a 5.4 liter. Shop has installed a new oxygen sensor for a P0135 (O2 heater circuit) code. New sensor and still same code. Now they are thinking it may have a bad PCM. I got called in and inspected the wiring. The connector for bank 1 sensor 1 is in an awful spot behind the passenger side of the engine. The clue that it may be a wiring issue is the newly installed remanufactured transmission. Bad things can happen to wiring when a transmission is installed especially to oxygen sensor wiring.
Well here it is the lock portion of one of the terminals for the heater circuit was broken. The terminal itself was also damaged. The terminal was being pushed out when the oxygen sensor was connected causing the heater circuit code.
Here is another one found with the eyes. Mitsubishi Montero with oxygen sensor codes. My first tipoff was the two different color connectors. Then a close inspection of the harness connector showed the locator tab was filed off. They used a left side sensor in the right side. They are all the same aren't they? Wire orientation was different. Very dangerous. Shop was lucky no PCM damage occurred.
A good technician not only uses his scantools, voltmeters, etc. He or she also utilizes sight, sound, smell, feel, etc. Pay attention to details and learn from your mistakes.