SPEEDO REGISTERS WHEN VEHICLE IS STATIONARY (INFORMATION)

SUBJECT: SPEEDOMETER REGISTERS WHEN VEHICLE IS STATIONARY (INFORMATION)

MODELS: 1988-93 C/K TRUCKS, 1989-93 S/T TRUCKS, AND 1990-93 TOPKICK/KODIAK TRUCKS

Some 1988-93 C/K, 1989-93 S/T and 1990-93 Topkick/Kodiak vehicles will register a speed, often as high as 12 MPH, when engine speed is increased with the vehicle stationary and the transmission in neutral.

This condition is due to the sensitivity of the vehicle speed sensor and is not an indication of a malfunction. When the engine is "reved up" normal engine vibration is transmitted through the transmission, causing the reluctor wheel used for speed sensing to also vibrate. Although the vibration is minute the sensitivity of the speed sensor is such that a speed signal is induced.

As previously stated, the vibration is normal and the level of sensitivity of the speed sensor must be maintained to accurately support vehicle systems such as cruise control and antilock brakes that require vehicle speed input.

When the vehicle is moving the spinning reluctor wheel overshadows any vibration that may be present and an accurate speed reading is maintained.

Since the condition is normal, no attempt to eliminate it should be made. Replacing parts will not be effective.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.