LS1 F-Body: How to Run Front Oxygen Sensors from Rear Sensor Harness
This will illustrate how to run front oxygen sensors using the rear oxygen sensor harness. This is necessary when installing long tube headers on a 1998-2002 LS1 Camaro/Firebird/F-Body. The car will throw Check Engine Light codes if the car has not had rear oxygen sensors removed from a PCM tune.
*This modification is intended for off-road use only. All applicable state and federal emissions laws apply.*
The purpose of this write-up is to save money from purchasing costly Corvette oxygen sensors, oxygen sensor extension harnesses or soldering in extensions. Any method used to lengthen the wiring will reduce the strength of the sensor signal and may lead to false readings by the PCM.
Tools Needed:
7mm socket (1/4” or 3/8” drive)
10mm wrench (or the size needed for the negative battery cable terminal)
small flat-tip screwdriver (not jewelers, though)
1. Disconnect the battery. Make sure to write down any radio codes, sound system settings, and/or other pertinent information. (The PCM will be disconnected, failure to disconnect the battery may result in damage to the PCM.)
2. Loosen the top connector on the PCM with the 7mm socket. The bolt will take an extended length of time to become free. Eventually, it will become free.
3. Lift the connector off, and move it aside leaving plenty of slack in the wires.
4. Remove the gray plastic cover, pushing in on the four tabs (on the ends).
5. Use the screwdriver to assist in pushing in the white tabs from the connector. This will give more slack in the wires.
6. Push in the white tabs under the blue cover (the one that ends in wire #40 and #80, 99-02 PCMs). It will pop off easily.
7. Remove the wire by LIGHTLY lifting on the plastic retainer. Slide the wire FORWARD further into the connector, and then push the wire BACKWARDS (put ar finger on the metal end, and give a slight but firm tug on the wire (as close to the metal connector on the WIRE side).
8. Make sure to record which wire is being removed. If it was the “Bank 1, Sensor 1 LOW” wire, then this will go into “Bank 1, Sensor 2 LOW” wire’s slot.
9. The 8 wires being switched are all colored. Each sensor has a solid wire and a striped wire. Pull the solid tan wire out, mark it with tape, then pull the second tan wire out, insert taped tan wire into un-taped wire’s spot. Other methods can be used for identifying the wires, but don’t remove them all at once.
Essentially, you are switching wires of the identical color from different locations.
10. Repeat for all 8 wires.
Pin out is as follows:
1999-2002 PCM:
TAN 25+26,
TAN-WHITE 28+29
PURPLE 65+66
PURPLE-WHITE 68+69
All 8 wires are next to each other. Tans on the top row, purples on the bottom row. Remove wire #25 mark it as #25, remove wire #26, insert into the slot for #25, then insert #25 into slot #26 and so on.
On a 1998 PCM, the pin-out and wire switching locations are different.
TAN 1+5
TAN-WHITE 2+6
PURPLE 41+46
PURPLE-WHITE 42+47
After pulling out a wire, when re-inserting it, make sure the plastic retaining tab catches the wire and that the metal end is flush with the other wires and is fully seated.
11. To reassemble, pop the blue cover back on (make sure the “indexed” side matches the orientation of the other blue cover).
The right side is “indexed.”
12. Snap the connector assembly back into the aluminum housing, ensuring all the white tabs fully snap into place and everything is flush.
13. Reinstall the gray cover (the wires might be difficult to tuck in, but they can be tucked back in). Note the left wires (bundle with oxygen sensor wires) go above the connector, and the right bundle of wires goes through the gray cover.
14. Tuck wires under the cowl, press on the connector to connect the wires back onto the PCM. Make sure it is seated evenly. Torque bolt to the specs on the cover, OR torque until it stops with hand pressure on the ratchet, then go 1/8 to 1/4 turn further.
15. Reconnect the battery, start-up, and ENJOY!
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