Prius (2004-09) :: Door Open (Ajar) Warning Light Staying On

My 08 Prius developed a hiccup yesterday. While driving down the interstate there was an occasional red flash from the dash. It would come and go so fast that by the time I could actually process it and focus it was gone. I had to stop by the dentist office as I was ready to walk out the door I heard a car in the parking lot with the horn/alarm sounding. I mentioned to the folks in the waiting room that someone alarm was going off. A lady replied that green Prius with the bike rack!

Sure enough it was mine! I was unable to find any causal factor. I left there and at my next stop, the horn/alarm started sounding just as I walked through the entrance door to Home Depot back to the parking lot. This time the Door Ajar/Open light on the dash was lit. I opened and closed all the doors and hatch. The Door Ajar light was still on I then manually manipulated all the door switches and opened/closed/slammed the hatch several times. No Joy I drove home.

About the only thing I was able to find was that it was probably the hatch, the switch is sealed within the locking/latch mechanism and that I could simply just unplug it. So I began troubleshooting.

After removing the rear hatch/floor, plastic bin, etc. I removed the plastic cover from around the latch (above the bumper not on the hatch lid), then removed the longer plastic cover that runs along the same area and provides the cover for the area between the rubber gasket and the inside of the hatch/floor area. Now I was able to see the latch mechanism and associated wiring (looking down toward the spare tire well). I also had the hatch light turned on (left side) which was easier to see than the Door/Ajar light on the dash.

I manually tripped the latch and the light flickered. I pressed down on the latch (hoping to put more pressure on the internal switch)…the light continued to flicker. Using a 10mm socket, I removed the latch, wiring retainers and disconnected the plug. The electrical plug, located about 8†to the left of the latch has 4 wires. The two on the bottom power the electrically operated latch and the two on top go to the Door Ajar switch (the one that is inside the latch assembly).

I noticed a little bit of corrosion and discoloration on one of the male pins (the plug that is connected to the latch end of the wiring). The female plug (connected to the car end of the wiring) also had some discoloration.

I plugged them back together and found that as I moved the wires/plug the light would flicker and change sometimes turning off. I unplugged it and connected my ohm meter (using small jumper wires with clips) to the two top (male) pins on the switch end of the plug. The switch tested fine. I even tested it with my homemade battery powered continuity light (wanting to test the switch under a load). I also wiggled the wires going into the plug itself, Perfect, no problems here! So, I determined the problem was truly with the plug itself. I also jumped the two female connectors with a short piece of wire (simulating the switch) and the light would come on (as it should have). OK, plug problem confirmed!

I cleaned the pins (both male and female), applied some dielectric compound and plugged it up. The light remained off for a few seconds then started flickering again! I could even hear a slight hissing sound coming from the plug (never a good sign). I tried tweaking the male pins (bending them slightly trying for a better connection) No Joy.

I clipped the wires (only the top two) from each end of the plug (red & white/black stripe wires coming from the latch).