Introduction: OBD II Codes P0420/P0430 Fix

About: Tinkerer

Do you have this annoying light on the dash of your Mustang? Have you changed your exhaust system? If you have installed an off-road h-pipe or x-pipe (no catalytic converters) or removed your catalytic converters for track use, your oxygen sensors will read a higher level of emissions which will trigger a check engine light or malfunction indicator light. If you have scanned the OBD II codes and have a P0420 and/or P0430 (Catalyst System Efficiency Below Limit) then I have a solution for you. As with most mods to cars, especially the emissions system, there can be fines or other penalties for using this on road; there is also the possibility of damage to your vehicle. That being said; let's fix your car.

Step 1: Parts and Tools Needed

Electrical parts you will need are:

2 - 1.0 uF 35V 20% Dipped Tantalum Capacitor

2 - 1M Ohm 1/2 watt resistors

Both of these are available from Radio Shack P/N's: 272-1434, Capacitors and 271-1356, Resistors

1 - package assorted Heat Shrink Tubing

1 - Package Electrical Solder

Tools needed:

Diagonal Cutters

Some type of wire stripper

Pittsburgh 6pc Carving Set from Harbor Freight

Soldering Iron

Heat source to shrink heat shrink tubing

1- Alligator Clip

Step 2: Bare the Wires

This procedure is being done on a set of O2 Wiring Harness Extenders.

In all the pictures the O2 sensor connector is to the right.

Pull the covering back off the wires and clamp with alligator clip. I pulled it back from the sensor end so I would remember which way the components go.

The wire colors in the extenders are NOT the same as the O2 sensor. Make sure you plug them into the sensor and write down what the matching colors are!

For example, mine were red=black, blue=gray, black=white, green=white. Make SURE YOU CHECK THE COLORS on YOUR CAR!!

The voltages are hugely different between the wires and WILL DAMAGE YOUR COMPUTER!

White Wire - 12V Heater +

White Wire - Heater Ground

Grey Wire - Output Signal

Black Wire - 450 millivolts reference signal sent from the computer

Step 3: Take Connector Apart

Use the tool from the Carving Set to pry out the red locking tab from the end of the connector.

Using the same tool pull the gray weather seal out of the back of the connector.

Next remove the two wires from the housing that correspond to the gray and black wires on the O2 sensor. Record where the two wires go into the housing.

This part is a little harder. Look inside the connector at the electrical contacts. About 3/8ths of an inch down you will see a little tab; use the tool to gently lift that tab and slide the electrical connector out of the housing.

Now gently pull the wires out of the weather seal.

Step 4: Adding Electrical Components

Solder the short lead from the capacitor to the lead on one end of a resistor. I used a pair of hemostats to protect the capacitor from heat damage (I solder slow).

Next, cut a piece of wire from the gray wire in the harness (or whatever color is used for the gray wire) the same length as the capacitor and resistor. (see picture)

Slip a piece of heat shrink over the wiring harness wires, then strip the insulation off.

Solder the components into the space where the wire piece was cut out.

IMPORTANT!! The resistor has to be on the side of the sensor connector and the capacitor has to be on the car side of the cut.

Step 5: Finishing Up

Slide a piece of heat shrink tubing over the black wire (or corresponding color), then strip off a section of insulation. Take the remaining lead from the capacitor and solder it to the bare wire.

Ok, all the connections should be made; it is now time to heat shrink all the connections.

As a final step, I slid a larger piece of heat shrink over the whole circuit and shrank it on.

To reassemble the connector, reverse the steps to take it apart. i.e. push the wires through the weather seal and into their proper holes in the connector. They should snap into the clip; then stuff the weather seal into the bottom of the connector. Finally press the red pin lock back into the front of the connector.

Take off the alligator clip and slide the cover back up over the wires and install in your car.

The last thing to do is if you have and OBD scanner that will reset the codes, use that to reset all your codes. If you don't have one, disconnect the negative cable off the battery for about five minutes; that should clear the codes.

This is a much cheaper and neater looking installation than many others I have seen on the 'net. Good luck on the dragstrip!

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