Sourcing O2 Sensors

Universal 4-Wire Heated O2 Sensors The O2 sensors used are 4-wire Heated sensors, identical to "Universal 4-wire Heated O2 sensors" but with the OEM connector on them. A very few vehicles have 3-wire sensors - so a visual verification of what your vehicle uses is necessary. With a Universal sensor the wire from the old sensor is cut, spliced/crimped & heatshrunk onto the new sensor. One US part number is Wells SU226, another is Bosch 13275, with another equivalent from Advance Auto Parts for 38$US. Another supplier is "Foreign Autopart, 630 Somerville Ave, Somerville, MA 02143 (or 02144) on 617-628-1441", at around 80$US per sensor. UK owners can obtain universal oxygen sensors from any Motor Factor in the UK.

Universal O2 sensors are circa £47/US$38-70, from Retail/Trade Motor Factors stores. OEM sensor even from Trussville Mazda USA are 140$US-180$US each, or £200 in the UK. Re-using the old connector/lead offers considerable saving.

For wiring, heater wires are both white, signal grey & signal ground is black, a standard 4 wire O2 sensor. Should your wire colours differ then the pair of same-colour wires are the heater.

O2 Sensor Life

Rear O2 sensor life is circa 60-80k miles and fails first. The front O2 sensor often lasts longer, around 80k-90k miles. O2 sensors do not suddenly fail, rather their response time (delta) to changes in the exhaust hydrocarbon (HC) content eventually becomes so slow that the ECU declares them to be an emissions failure and sets a Check Engine Code accordingly. Once an O2 sensor is performing outside the required specification the engine will no longer use their input during part throttle (closed loop) operation and substitute it's own "limp mode" value. During limp mode fuel (HC) emissions are greatly elevated and fuel wasted (3-4mpg).

Fitting Rear O2 Sensor

1. Ensure the handbrake is firmly applied and the car is in gear or Park. Jack the car up using a good hydraulic jack under the front Jacking Point and support the vehicle on axle stands.

2. Remove the right front wheel, viewed from the rear and look directly into the engine area until the vertical exhaust downpipe is located. Following the downpipe down about 1/3 of the way up from the bottom above the steering rack a bright green cable sheath can be located, the rear oxygen sensor.

3. Using an oxygen sensor spanner & extension, reach in to remove the sensor which should come free easily. This method avoids going under the vehicle and is thus suitable for home DIY maintenance.

4. Allowing the original O2 sensor to dangle freely, verify your new O2 sensor will fit correctly and matches the number of wires on the original sensor.

5. Looking at the top rear of the engine, locate the rear O2 sensor connector by following the cable upwards until it meets the left-rear of the aluminium VRIS casting. It will be situated underneath the rear of the casting and clipped to a mounting plate. Unplug the O2 connector with care via a press-to-release latch. A torch may be needed along with more patience than commonly available.

6. With the O2 connector released, remove the O2 sensor completely from the car. There will be two cable ties holding the cable to the power steering hose, these two cable ties need to be cut without damage to the power steering hose. Also ensure the power steering hose is not pushed near the exhaust downpipe.

7. Position in front of you the old & new O2 sensors. Examine the leads from the new O2 sensor, most likely they will match the old sensor (2-white, 1-black, 1-grey). Do not damage the anti-seize coating applied to the new O2 sensor.

After verifying that the leads match, cut the old sensor off its cable in a staggered fashion about 2" from the sensor. The individual wires should be cut so that the rejoined connections can't touch even if all the insulation should fail. The remaining cable & connector are spliced onto the new O2 sensor. Re-use any high temperature shielding (glass fibre/fiber braid) and put the heatshrink on the individual wires BEFORE crimping them.

Crimping of wires should really be done with a proper (read 30$+) tool, and any soldering should be done with silver-solder since the wires are stainless steel. Once crimped, the individual wires must be covered in heatshrink. Both crimps, heatshrink and instructions are provided with all Universal O2 sensor kits.

8. Verify all connections are secure, properly insulated, and any high-temp sleeving is re-used. Now finished, prepare to install the sensor.

9. Lower the sensor down the same route into the car, but do not plug it into the harness. Tie a piece of string to the end to stop it falling through. The string prevents the connector being twisted & falling during sensor tightening.

10. Underneath the car refit the O2 sensor into the hole, and torque to 30-49Nm/22-36lb/ft. Then move up to the top of the car and then connect the O2 connector into the car's wiring harness. Cable tie the cable twice to the power steering hose as it was originally.

11. Remove jack stands & lower the vehicle. The task has now been completed. If an O2 error code was obtained from the ECU, it must be reset by disconnecting the negative battery terminal for 2 minutes and opening a passenger door. The car will relearn its idle over the next few days of driving. The ECU does not reset it's own codes.

Fitting Front O2 Sensor

1. Lift bonnet/hood with the car on a level surface. Locate and remove the cold air duct running across the top of the radiator via the two 10mm nuts.

2. Looking down above & to the right of the oil-filter, the front O2 sensor is clearly visible emerging from the exhaust downpipe. Identify the O2 sensor cable and locate the wiring harness connector to which it is connected. Pressing the releasing clip of the connector (sometimes it helps to press the connector together during this), unplug the connector carefully.

3. Unscrew the O2 sensor.

4. Position in front of you the old & new O2 sensors. Examine the leads from the new O2 sensor, most likely they will match the old sensor (2-white, 1-black, 1-grey). Do not damage the anti-seize coating applied to the new O2 sensor.

After verifying that the leads match, cut the old sensor off its cable in a staggered fashion about 2" from the sensor. The individual wires should be cut so that the rejoined connections can't touch even if all the insulation should fail. The remaining cable & connector are spliced onto the new O2 sensor. Re-use any high temperature shielding (glass fibre/fiber braid) and put the heatshrink on the individual wires BEFORE crimping them.

5. Verify all connections are secure, properly insulated, and any high-temp sleeving is re-used. Now finished, prepare to install the sensor.

6. Rescrew the new O2 sensor in place of the old and torque to 30-49Nm or 22-36lb/ft. Reconnect the O2 connector to the car wiring harness.

7. Remove jack stands & lower the vehicle. The task has now been completed. If an O2 error code was obtained from the ECU, it must be reset by disconnecting the negative battery terminal for 2 minutes and opening a passenger door. The car will relearn its idle over the next few days of driving. The ECU does not reset it's own codes.

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