DP Fix Bypass Switch

Bill of Materials:

1. Pins for Tyco MQS series - Tyco 2-963725-1
2. Receptacles for Tyco MQS series - Tyco 963726-1
3. Switch - McMaster 7347K82
4. Boot - McMaster 70205K3
5. Shrink Tube - McMaster 7856K131
6. Wire - McMaster 69835K341

Theory of Operation:

With the switch in one position, the signals from the rear O2 sensors will be fed into the DME for normal driving. With the switch in the other position, the simulated signal from the DP Fix will be fed into the DME for inspection time.

Schematic:

DP_Fix_Bypass.pdf

Procedure:

1. Extract the wires from the DME connector as described in the DP Fix instructions. *Make a note of which yellow wire goes to pin 19.* You can wrap a tape "flag" around this wire temporarily.
2. Figure out where you want your switch and drill a hole in the white box (1/4"). I mounted mine on the front side of the box, near the outside so I can reach it with the cowl cover in place.
3. Cut off the two female terminals on the black wires of the DP fix. Leave equal lengths of wire on the DP Fix and the terminal ends. The two wires with the female terminals will connect to the center terminals of the switch and to the DME. The two ends of the black wires from the DP fix will connect to the bottom terminals of the switch. Add 12 inches to each of the wires (4) and cover the splices with shrink tubing.
4. Cut a "window" in the insulation for the black wire with a male terminal on the DP Fix. Use your wire strippers to cut the insulation in two places about 1/4" apart. CAREFULLY use a sharp knife to slit the cut section of insulation so that it may be removed from the wire. Solder the end of 12 inches of wire to this window. Slide shrink tube over the splice.
5. Solder one of the extra male terminals you bought to the end of 12 inches of black wire. Carefully use pliers to clamp down each side of the insulation barrel over the insulation of the wire.
6. Place the DP Fix in the white box, and route all wires to allow for neat installation. Refer to the schematic for guidance. Run the wires that go to the switch through the 1/4" hole to judge how long they need to be. Once all wires are neat and in place, cut off the excess hanging outside the box through the hole.
7. Solder the wires which attach to the DME pins 19 and 20 to the center terminals of the switch on each side. Ensure you place shrink tube over the wire BEFORE you solder it. Slide the shrink tube over the switch terminals and shrink it. *Make sure you know which side goes to pin 19.*
8. Solder the black wires from the DP fix to the bottom terminal of the switch. Apply shrink tube as directed above.
9. Solder the end of the black wire connected to the male terminal of the DP fix to the side of the switch which is connected the pin 19 on the DME. Apply shrink tubing.
10. Solder the other black wire with the male terminal to the other side of the switch. Apply shrink tubing.
11. Install the switch and boot in the hole.
12. Slide shrink tube over the black wire of the DP fix with the male terminal. Insert the male terminal into the female terminal on the yellow wire which you removed from pin 19 on the DME connector. Shrink the tubing over the connection to secure and insulate it.
13. Repeat step 12 for the other black wire with a male terminal and the other yellow wire which was removed from position 20.
14. Insert the black wires with female terminals into the DME connector. Ensure the proper wire is inserted into position 19.
15. Follow the DP fix instructions for the red wires.

Notes:

1. Practice makes perfect when heating shrink tubing with a lighter. Just get the flame close, it does not have to actually touch the tubing. You could use a heat gun if you prefer.
2. The switch has six terminals. Holding the switch so that there are three terminals on the right, and three terminals on the left, each side is one circuit independent from the other. With the level in the up position, the center terminals on each side are connected to the bottom terminals on each side. With the lever down, the center terminals on each side are connected to the top terminals on each side. The terminals on the left are never connected to the terminals on the right.
3. If a wire crosses another in the schematic and there is NO DOT, the wires are NOT CONNECTED. Dots indicate wire which are connected.
4. You only really need one male terminal, but buy five or ten of each in case you need to correct a mistake.
5. If at some point you connect the wrong O2 sensor to the wrong input on the DME, you will throw a code. Pay attention to which sensor connects to pin 19, and the other must connect to pin 20.

The coffee was extra strong this morning so I may have overlooked something in my caffeine induced ADHD frenzy.

Attached Images

• DP_Fix_Bypass.pdf (42.5 KB)