Replacing the C4 Oxygen Sensor

Time: 30 Minutes

Tools: Special oxygen sensor socket, 3/8” ratchet and extensions

Talent: (2)

Applicable Years: 1984 to 1996

Tab: $40.00 to $200.00

Torque Numbers: 40 to 44 lb./ft.

Tip: It’s often easier to remove the sensor if the exhaust is still hot, rather than after the entire system has cooled down. You may need several different socket extensions and a universal joint for your ratchet wrench. Also, make sure you use a proper O2 socket for the sensor and use antiseize compound on the threads when you install the new sensor.

Performance Gain: The biggest difference will be improved idle performance. You could see a performance gain across the board depending on how badly the  O2 sensor was deteriorated.

You probably won’t have to replace the O2 sensor on your Corvette. On the other hand an Oxygen sensor is cheap enough that you might want to simply replace the sensor every 50,000 miles as part of a routine maintenance program.  Even if you own a C4 with the LT1 engine, and two sensors, the price is still cheap. Treat it like a spark plug and replace it before it causes a problem.

The oxygen sensor is a key element in the engine computer system while the car is operating in closed loop system. The data from this sensor is used to maintain a balanced air/fuel mixture. If the sensor is sending out false or even sluggish readings then your engine is not going to be at peak performance.

An oxygen sensor need not fail completely. Often times on older cars they simply start to act sluggish. The usual signs of this are a slight loss of power, a rougher idle, or a slight drop in fuel mileage coupled with increased emissions.

Almost any shop can hook a scan tool to your Corvette and read the number of oxygen sensor counts, or the number of times it’s actually measuring your exhaust gases. This is a foolproof diagnosis and might eliminate an unnecessary replacement, although the diagnosis may cost more than a new oxygen sensor.

Depending on which engine is in your Corvette you may have to look for the oxygen sensor in two different places. On the L98 engine there’s only one sensor. It’s located down on the exhaust pipe, on the driver’s side just forward of the catalytic converter.

The ZR-1 uses two oxygen sensors, which are located forward of the catalytic converters. These are both heated, which means the price is about double that of the older style. The procedure for removing them is no different from replacing the single sensor in the L98.

Before you start to remove an oxygen sensor it’s a good idea to remove the negative battery cable. Anytime you do electrical work on your Corvette it’s not a bad idea to disconnect the battery. This is especially true when you start  messing around with any of the sensors. Although it’s not critical when removing the  O2 sensor you might feel safer with the battery disconnected.

Most oxygen sensors come with the threads already coated with a special anti-seize compound. GM uses a special compound composed of graphite and glass beads. The graphite will quickly burn away, but the glass beads will remain. If you have to remove and reinstall the old oxygen sensor(s) make sure that you coat the threads with an anti-seize compound.

CC-2-1CC-2-1: The LT5 engine has two oxygen sensors, and both are fairly easy to reach with a wrench. The bad part is they’re very expensive. A single sensor is roughly twice as much as an LT1 sensor. That’s because they use a heated tip to keep the emissions clean at start up.

CC-2-2CC-2-2: When the LT1 engine was introduced the Corvette returned to a true dual exhaust system. This meant that the system had to have two O2 sensors – one for the right side and one for the left side. The good part is that they’re fairly easy to get to.

CC-2-3CC-2-3: This special socket is used to remove the O2 sensor from the exhaust system. The slit down the side is a provision for the wiring. I would disconnect the harness first. Then you might as well start out with a half inch breaker bar on the end of this socket since these sensors don’t like to be removed. In some cases you can use a box end wrench and just thread the wires through the box end.

This is an adaptation from Richard Newton’s most recent book 101 Projects for Your Corvette 1984 – 1996. He has also written two other best selling Corvette One deals with the 1968 to 1982 Corvettes, How to Restore and Modify Your Corvette 1968-82 , while another deals with the Sting Rays from 1963 to 1967. All  of these books are available from Corvette Central.

9 thoughts to “Replacing the C4 Oxygen Sensor”

  1. Running rich with black smoke coming out change air filter and still. Runs and idles fine , just when I step on gas black, not blue smoke comes out. O2 sensors?

    1. Bad 02 sensor is a definite possibility. That would be a good place to start. If the check engine light is on, check the codes first, then proceed. If it is not an 02 sensor issue, it could be fuel injectors, ignition issue, etc.

  2. I have a 1990 vette had the o2 sensor replaced still doing the same thing. Had another mechanic tell me there 4 o2 sensors. True or not??????

  3. Would removing the mufflers have any effect on o2 sensor failing? Ever since I removed the mufflers the idle took longer to come down to 800 rpm’s like it did before. The car runs fine till it hits 170 degrees. I installed a new msg optispark and replaced ignition coil last year. The car was fine for almost 1 year after opti install.

  4. My 92 C4 is showing “h22” TPS Low so I replaced it and it ran great for 2 miles now it’s back to barely running. It also shows H64 O2 lean exhaust. I haven’t replaced the o2’s yet. Could something else be causing these codes?

  5. My 94 c4 LT1 stumbles and backfires through the throttle body. Have changed opti/wires/plugs/ECM/fuel pump and injectors with new fuel pressure regulator. Sure could any input you may have.

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