This 2000 Ford Taurus came in with the complaint that the a/c did not work. The customer had already figured out that the 15 amp fuse number 28 in the underhood fuse box was blown. It is worth noting that in the wiring diagrams that fuse is referred to as fuse number 128.
Power on one side.
No power on the other side. The fuse is blown.
The a/c compressor relay.
I installed a new fuse and unplugged the relay. Started the engine and turned the a/c on. I installed the relay and watched for the fuse to blow. Nothing happened. I checked the terminals at the relay socket and found that I did not have power there. Rechecked the fuse and it was blown. Did I not see or hear the fuse blow? Let’s try this again. Installed another new fuse. Checked to make sure that the fuse had power on both sides and that I had power at the relay socket. All was well. I started the engine and turned the a/c on. Before I installed the relay I wanted to confirm that there was still power at the relay socket. No power and the fuse was blown. Okay the compressor is not the culprit in this case. Time to look at the wiring diagrams.
The wiring diagrams showed that the oxygen sensor heater elements were connected to this fuse. I checked the wiring at the front O2 sensor and all was well. I went to check the rear O2 sensor wiring. Pretty hard to see, so I used a mirror. I found the O2 sensor connector laying on the EGR valve tube.
After some disassembly I got the connector out to be able to repair the problem. I had to install a new O2 sensor and a new harness connector.
I also investigated to find the reason for the connector laying on the hot EGR valve tube. I seem as if someone had changed the DPFE sensor. They could not get one bolt undone. So they mounted it with one screw and rerouted the hoses going to the DPFE sensor. Well in doing all of this the connector was forced off of its’s mounting location and fell on the hot EGR valve tube. I removed the screw using a pair is vise grip pliers to grab the stripped head. Properly mounted the DPFE senor and correctly routed the hoses. I then secured the O2 sensor sensor connector to it’s mounting clip.
Another one done. Sad that the whole thing could have been avoided with quality workmanship on the DPFE sensor replacement. In case you were wondering the DPFE stands for Delta Pressure Feedback Exhaust. It measures the pressure difference in the exhaust system at two different points. The sensor sends a voltage signal to the PCM. The PCM uses that signal to determine if the EGR valve responded to the PCM command to open. A malfunction usually results in a code P0401 insufficient EGR flow.