2004 C70 Trunk/fuel door switch not working

dcaton · Post by **dcaton** » 21 Oct 2018, 16:08

The trunk opens fine with the key fobs, so the latch is working correctly. The switch on the driver's door panel tests ok. Center contact seems to be common, outer two contacts test ok when buttons are pushed. Nothing happens when I short the center wire on the connector (black) to either of the other two wires (white/yellow and gray/blue).

There's no obvious chafing or wear on the wiring harness, nor is there any significant voltage between any of the three wires and ground. I expected the common wire to have +12v, but maybe not if it's just a switch closure input to the computer or some other module that controls the trunk and fuel door.

Something else is strange. First thing I checked is the trunk lid fuse (fuse #1). The fuse is fine but I don't get any voltage reading between either fuse terminal and the battery negative terminal. However, I do get 12v between either fuse terminal and the battery positive terminal. That doesn't make any sense. Surely the fuses aren't in the negative side of the circuit, are they? Doesn't really matter, just curious. If I remove the fuse the key fob won't open the trunk, so the circuit is functioning regardless of how it's wired.

Appreciate any help or even a wiring diagram. I have no idea where the wires from the switch go.

Edit: Ok, found the wiring diagram for a 2000, I hope it's the same for a 2004. I don't quite understand these diagrams but the diagram on page 287 shows the wires from the door switch (3/109) going into the door lock/unlock switch (3/97). Apparently there's a bunch of diodes in there, which I guess forms some sort of switching matrix. It all seems to end up in a box (2/76) under the dashboard somewhere.

Post by **wizechatmgr** » 21 Oct 2018, 17:53

Try depressing lock and unlock 3 times. Make sure it ends with unlocked. On my '99 I had a locking bad switch that was causing the gas flap to be disabled.

quietlymknnoise67 · Post by **quietlymknnoise67** » 21 Oct 2018, 18:16

My 03 C70 has the same problem the switches on the driver's door do not activate either the trunk lid nor the gas door. The key fob will unlock the trunk then I pull the manual cord to open the gas door. I did replace the switches and no change.

dcaton · Post by **dcaton** » 21 Oct 2018, 19:33

It's fixed. After I saw on the wiring diagram that the trunk/gas switch fed into the window/door lock switch, I took a look at the window/door lock switch. After I disconnected and reconnected the connectors, the trunk/gas switches worked again. So either one of the connectors on the window/door lock switch wasn't fully seated, or maybe there was a bit of corrosion on one or more of the connections. Looks like these circuits are logic circuits, not higher voltage circuits that directly power the trunk release or gas cap solenoid, so a little bit of corrosion would likely keep it from working.

I certainly wasn't expecting the trunk/gas switch to have anything to do with the window/door lock switch but I suppose if the window/door lock switch was faulty then it could also affect the trunk/gas door switches. quietlymknnoise67, you may want to check the window/door lock switch to see if you have the same problem. Or just replace it.