THROTTLE POSITION SENSOR REPLACEMENT INFORMATION

Models Affected: 1989-90 6000, GRAND PRIX AND FIREBIRD MODELS WITH 2.8L AND 3.1L ENGINES

Application: 1990 LHO 3.1L - 6000, Grand Prix, and Firebird Models 1989 LHO 3.1L - Grand Prix Models 1989 LB6 2.8L - 6000, And Grand Prix

This information bulletin is issued due to the number of throttle position sensor (TPS) replace (J-6374) warranty claims on the vehicles listed above.

Beginning with the 1989 model year, all 2.8L and 3.1L engines have a non-adjustable TPS (with the exception of the 1989 Firebird). TPS Adjust Labor Operation has been eliminated as of June 1, 1989 on all above vehicles.

All GM fuel-injected engines with IACVs use TPS auto-zero function in the ECM software, minimizing the need for TPS adjustments. The computer software on these applications is designed to auto-zero the TPS to 0% or 1% at closed throttle (an ALDL scan tool which indicates percent throttle will check the auto-zero function).

METHOD FOR CHECKING TPS FOR REPLACEMENT:

A new method to check closed throttle TPS with the Auto-Zero system has been developed.

IF THE CLOSED THROTTLE (% THROTTLE) IS 0% OR 1% WITH NO INDICATION OF CODE 21 OR CODE 22, THERE IS NOTHING WRONG WITH THE TPS.

If the closed throttle % throttle position is NOT 0% or 1%, check the TPS voltage. The allowable voltage range for the closed throttle TPS is 0.29 - 0.98 volts, using a Tech I scan tool. If a TPS failure is indicated by CAMS or other diagnosis, and the voltage is within 0.29 - 0.98 volts, DO NOT REPLACE OR ADJUST THE TPS.

If throttle reading is greater than 1% while the voltage is between 0.29 and 0.98, the ECM has an invalid closed throttle TPS voltage stored in its keep-alive memory. To have the ECM show the correct values, the TPS connector should be disconnected with key "ON" and then reconnected with key "OFF" to automatically reset the throttle reading to 0%.

Use applicable labor operations and times.

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.