Where Is the Knock Sensor on a 1995 Impala?

The Impala SS once was the king of the full-sizes from the late 1950s to early 1970s. Emissions regulation, including catalytic converters and the elimination of leaded fuel, were the main culprits for its slow demise through the 1970s and its eventual elimination in 1985, despite a near comeback in 1977. In 1994, the Impala SS name made a triumphant return to Chevys lineup as a more powerful and better-looking version of the Caprice, which marked the second time the Caprice and Impala crossed paths. The 1995 Impala SS came fitted with a 260-horsepower, 5.7-liter V-8 engine. On each side of this engine was a knock sensor, which would sense excessive engine knock and instruct the vehicles computer to retard the ignition timing until the knock disappeared. Replacing the knock sensors is straightforward; you just have to figure out where Chevy hid them.

Instructions

Raise the front of the Impala with a floor jack and slide jack stands under the vehicles frame rails. Slowly lower the vehicle onto the jack stands.

Crawl beneath the drivers side of the Chevy and find the downpipe from the exhaust manifold.

Look just in front of the downpipe and find the sensor screwed into the engine block; this is one of two knock sensors on the engine. Look in the same place on the passengers side of the engine to find the other knock sensor.

Raise and support the Impala.

Squeeze the sides of the wiring harness on one knock sensor to unlock it, then pull the harness from the knock sensor.

Switch a multimeter to its ohm-measuring feature. Touch the positive lead of the multimeter to the pin inside the knock sensors receptacle, then touch the negative lead of the multimeter to the engine block, near the knock sensor.

Read the ohms displayed by the multimeter. If the knock sensor is in good condition, the multimeter display reads between 3,300 and 4,500 ohms, and you may proceed to the next step. If the resistance is not between 3,300 and 4,500 ohms, you need to remove and install a new knock sensor.

Turn the multimeter to the 2-volt AC current setting and start the Impalas engine. Move the negative lead to the negative battery terminal while holding the positive lead on the pin inside the knock sensors receptacle.

Lightly strike the engine block near the knock sensor with a hammer and watch for a small positive voltage reading to appear on the multimeters screen. If no voltage shows, turn the engine off and install a new knock sensor. If voltage appears, the sensor is operating correctly and you may turn the engine off.

Repeat the entire process to test the second knock sensor.

Raise the vehicle off the jack stands with a floor jack, then remove the jack stands. Lower the Impala to the ground.

Raise the front of the Impala with a floor jack and slide jack stands under the vehicles frame rails. Slowly lower the vehicle onto the jack stands.

Squeeze the sides of the wiring harness on one knock sensor to unlock it, then pull the harness from the knock sensor.

Remove the knock sensor with a ratchet and deep-well socket.

Thread a new knock sensor into the engine block by hand, then tighten it to 14 foot-pounds with a torque wrench and deep-well socket.

Plug the wiring harness into the receptacle on the new knock sensor.

Repeat steps 2 through 4 to replace the knock sensor on the other side of the engine, if needed.

Lower the vehicle to the ground.