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Tuesday, November 26, 2013

How to Check the Speed Sensor on a 99 Chevy Silverado

When the speed sensor on a 1999 Chevrolet Silverado begins to fail, the first noticeable sign may be a fluctuating speedometer. The speedometers needle may jump from one speed to another, or fall to zero and then suddenly return to the correct speed. The vehicle speed sensor, or VSS, is the sensor responsible for relaying the vehicles speed to the engine computer. In addition to using data from the VSS to calculate the vehicles speed, it also uses this data to make other computational decisions, including when to shift the transmission. The VSS is located on the tailshaft of the transmission or on transfer case in four wheel drive models. The sensor itself is a magnetic inductive sensor that monitors the magnetic field around a notched, reluctor wheel affixed to the tailshaft. The notches in this wheel interfere with the sensors magnetic field and the engine computer calculates the frequency of this interference and converts it into a speed value.

Instructions

Turn off the engine, but leave the ignition on. Connect a scan tool to the Silverados scan tool terminal.

Navigate to the live data menu and select VSS. Test drive the vehicle in a safe, controlled area such as an empty parking lot where there is no possibility of hitting other cars or objects.

Look down at the scan tools display and note the speed value for the VSS. It should reflect the vehicles current speed. If the speed displayed is 0 or different from the speedometer reading, its likely there is a problem with the VSS or the VSS harness connector.

Note the voltage value for the VSS on the scan tool. This value should be listed below or above the VSS speed value. It should read between 1.5 and 12 volts. If the value is outside this range, the VSS is either not receiving the proper voltage or is faulty.

Raise the vehicle with an automotive jack and support it with jack stands. Locate the VSS on the tailshaft of the transmission of transfer case for vehicles equipped with four wheel drive. Disconnect the VSSs electrical connector.

Turn the ignition on and probe the light blue wire on the connector with a digital multimeter set to DC volts. The multimeter should show between 1.5 and 12 volts. Connect a test lamp to a positive voltage source and probe the black, ground wire on the VSS connector. The test lamp should illuminate if the ground properly connected. If the ground is OK and you find voltage at the connector, then the VSS is faulty and needs to be replaced.

Sunday, October 13, 2013

How do I Determine Which Fuel Pump Is Needed for a 99 Chevrolet Silverado V6

General Motors engineered the fuel system of the 1999 Chevrolet Silverado V6 4.3L with and without an evaporative emissions system monitoring system. Chevrolet designed the fuel pump as an integrated module assembly, combining the fuel pump and fuel level sensor together as a single unit. Delphi manufactures fuel pumps for General Motors. 1999 Chevrolet Silverados equipped with the evaporative emissions monitoring system also have a pressure sensor built into the fuel pump module assembly. The engine computer applies vacuum to the fuel tank and monitors the sensor to verify the tank holds the vacuum. If the tank leaks, pressure drops and the check engine light will turn on.

Instructions

Park the vehicle on a flat surface such as a driveway. Set the parking brake and remove the keys from the ignition.

Chock the front tire of the 99 Silverado with wheel chocks to prevent the vehicle from rolling.

Lift the left rear drivers side tire of the 99 Chevy with the floor jack. Place a jack stand under the axle tube for safety.

Remove the plastic lug nut covers by hand using a 3/4 inch impact socket.

Remove the lug nuts using the 1/2 inch drive impact wrench and a 13/16 inch socket. Remove the left rear tire.

Lean into the wheel well toward the front of the bed. Shine the flashlight onto the top of the fuel tank. Extend the inspection mirror to inspect the top of the fuel pump module assembly.

The fuel pump module assembly is round where it inserts into the tank, and has three fuel lines attached to it. The fuel pump module assembly also has a square four-wire harness plugged into it to provide power to the fuel pump and to measure the fuel level.

Look for a small black sensor with a wide flat three-wire harness plugged into it. Also inspect the four-wire fuel pump harness for a tag with three prominent letters printed on it.

Vehicles equipped with evaporative emissions monitoring have the black sensor, two wiring harnesses plugged into the fuel pump module assembly and have a code on the four-wire fuel pump harness labeled "TCF." Delphis aftermarket part number for this fuel pump module assembly is FG0053.

Vehicles without evaporative emissions system monitoring do not have the black sensor, only have one wiring harness plugged into the fuel pump module assembly and have a code labeled on the four-wire fuel pump harness labeled "TCU." Delphis aftermarket part number for this fuel pump module assembly is FG0271.