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The oxygen sensor in a car is now an integral part of the exhaust system. Although it has been around for many years--since the implementation of On-Board-Diagnostics II in 1996--the amount of oxygen sensors per car has doubled. Finding them for replacement is now much trickier.

Location

The oxygen sensors are located directly in the exhaust system, usually by portholes that the sensor screws into on the exhaust pipes--and in some cases, on the exhaust manifold. The exterior portion of the sensor provides a wire and plug that plugs the harness into the ECU and transmits the voltage for monitoring.

History

Designed in the 1960s by a Robert Bosch, the oxygen sensor in a car made its first introduction in the late 1970s on a Volvo that also introduced the 3-way-catalyst system. By 1981, to reduce emissions, all vehicles were being manufactured with catalytic converters.

Function

The function of the oxygen sensor (also known as the Lambda sensor) is to monitor the amount of fuel-to-air mix in the combustible engine of a vehicle. The sensor transmits voltage and the engine management computer (ECU) monitors the ratio. There is an ideal ratio--when a sensor fails or there is an internal problem with the engine, more pollutants emit from the exhaust.

Types

The older sensors were "unheated" sensors. Since they do not transmit voltage until their internal temperature reaches 600 degrees Fahrenheit or more, this allows a period of time in between the ECU being able to monitor the sensor. "Heated" sensors are common today, have extra wires for the heating element and assist in heating the sensor more rapidly.

Considerations

If replacing an oxygen sensor, a direct-fit replacement is far superior to the "universal" sensor which would require cutting, identifying and splicing the wires of the sensor. The direct-fit sensor provides the necessary wires and plug to fit the plug of the wire harness easily.

Ford equipped the 1992 Bronco XLT with a 4.9-liter V-6 engine bolted to a five-speed manual transmission as standard equipment. A four-speed automatic transmission was an option, along with the choice of a 5.0-liter or a 5.8-liter V-8 engine. Use a hand-held scan tool such as Fords Self-Test Automatic Readout tester or an equivalent on your Bronco XLT to access the on-board diagnostics.

Data Link Connector

OBD2 came about in 1996 because of the Environmental Protection Agencys Clean Air Act. Prior to that, the on-board diagnostic system was not standardized and each manufacturer had its own system of diagnostics accessed through a data link connector mounted somewhere on the vehicle. Access the OBD system on your 1992 Bronco through the DLC located in the engine compartment. The DLC is mounted on the driver-side wheelwell on the front side of the shock tower.

A single pole double throw, or SPDT, relay is the most common type of relay used in the automotive industry. This relay has multiple pins and is commonly located alongside fuses and other relays in automotive applications. In a 1999 Mercedes-Benz ML320, there are two locations for the SPDT relays. The primary relay location is on the right side of the engine compartment, inside the main fuse box. The second location is above the passenger side foot well. The primary engine fuse box contains relays for the anti-lock brakes, ignition system, cooling fans, and other primary systems. The secondary fuse box contains relays for most of the interior systems, such as the radio and door locks.

Instructions

Primary Fuse Box

1

Turn off the ML320s engine and open the hood.

2

Shine a work light in the back-right corner of the engine, near the firewall.

3

Locate the primary fuse box. It is a large black box, made from high impact plastic.

4

Release the snaps on the box cover. Remove the cover to expose the relays and fuses inside the fuse box. A diagram is printed on the underside of the cover detailing the function and location of each fuse and relay within the box.

Secondary Fuse Box

5

Open the front passenger door.

6

Shine a work light underneath the dashboard.

7

Look on the upper right side of the foot well area. The secondary fuse box is mounted on the upper-right side of the foot well area. This box is a smaller, square box made from the same black plastic.

8

Remove the black cover on the secondary fuse box by depressing the plastic locking tabs. There is also a diagram on the underside of the secondary fuse box cover that details the locations of the relays and fuses within the secondary fuse box.