PDF associated:
/PT 20-0031.pdf
JDB0362 PT 20 0031 Application Problem Cause Solution Note 1997 1998 GM GMC Sport Utilities Astro Express Safari Savanna 1997 2001 GM GMC Pickups Silverado Sierra Steering that unexpectedly twitches or jerks in a turn at highway speeds or has no assist Vehicles equipped with VES rely on the steering wheel position sensor the Electronic Variable Orifice EVO valve and the ECM to control steering assist Any of these components could affect the steering assist Sensor Test If the steering wheel position sensor is bad the vehicle ECM in most cases will detect this and set a Diagnostic Trouble Code DTC If no code is set temporarily disconnect the senor then see if erratic assist stops or assist returns If operation returns to normal perform tests on the sensor wiring to ECM and the ECM Please refer to the vehicle service manual for detailed sensor testing and repair procedures The graphic below shows the typical sensor location on the steering column EVO Test The EVO valve controls the power assist provided by the power steering pump Even if this component fails no DTC s are set in the ECM Please refer to Pro Tech PT 20 0024 for EVO information and test tips ECM The ECM or on some applications a special EVO module directly controls the EVO Failure of the ECM or the vehicle speed sensor the steering wheel sensor or the EVO can cause assist problems Repair or replace as necessary Verification of proper function of all these components should be performed before replacing any of these components Please refer to your vehicle s service manual for specific diagnostic instructions This ProTech bulletin is supplied as technical information only and is not an authorization for repair Erratic Steering Assist on GM Variable Effort Steering VES Vehicles
