TPS - Adjustment/Replacement Information

9218chevy05

Number: 90-83-6E

Section: 6E

Date: November 1989

Corporate Bulletin No.: 936527


Subject:
THROTTLE POSITION SENSOR (TPS) REPLACEMENT INFORMATION


Model and Year:
1989 A, F, J, L CARS WITH 2.8L (VIN CODE W) ENGINE 1990 W CAR WITH 3.1L (VIN CODE T) ENGINE


TO: ALL CHEVROLET DEALERS

Beginning with the 1989 model year, all 2.8L and 3.1L engines have a non-adjustable TPS (with the exception of the 1989 F-car). 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%.