SERVICE MANUAL UPDATE SEC. 6E3 NO PWR./SPARK TIMING FIXED. Geo Storm 1991

THE FOLLOWING IS ADDITIONAL INFORMATION TO BE ADDED TO THE 6E3-C1 SECTION OF THE 1990-92 GEO STORM SERVICE MANUAL 1.6L SOHC AND 1.8L DOHC (VIN 6 AND 8). IN SECTION C1 ELECTRONIC CONTROL MODULE (ECM) AND SENSORS UNDER THE HEADING OF POWER STEERING PRESSURE SWITCH ON PAGE 6E3-C1-4 ADD THE FOLLOWING INFORMATION:

THE ECM MONITORS THE POWER STEERING PRESSURE SWITCH (PSPS) INPUT FOR AN INDICATION OF THE STEERING WHEEL BEING CRAMPED. WHEN THE PSPS MAKES SUCH AN INDICATION, THE ECM WILL ALTER SEVERAL FUNCTIONS. THESE FUNCTIONS ARE AS FOLLOWS:

* THE A/C COMPRESSOR CLUTCH IS SHUT "OFF" FOR UP TO 15 SECONDS. * THE ELECTRONIC SPARK TIMING IS SET TO A FIXED LOW VALUE UNTIL THE PSPS INDICATES THAT THE STEERING WHEEL IS NOT "CRAMPED." IF THE STEERING WHEEL IS "CRAMPED", SPARK TIMING WILL BECOME FIXED AT BETWEEN 6-10 DEGREES. * THE IDLE AIR CONTROL VALVE WILL ALSO BECOME FIXED AT SPECIFIC STEPS.

THE FOLLOWING INFORMATION IS TO BE ADDED TO SECTION 6E3-B SYMPTOMS SECTION. THIS INFORMATION IS TO BE ADDED UNDER THE HEADING OF "LACKS POWER, SLUGGISH OR SPONGY." ADD THE FOLLOWING TO "ADDITIONAL CHECKS":

* REVIEW THE TECH 1 TYPICAL SCAN DATA VALUES. NOTE THE STATUS OF THE POWER STEERING PRESSURE SWITCH, IT SHOULD INDICATE "NORMAL." IF THE DISPLAY IS "HIGH PRESSURE" AND THE STEERING WHEEL IS NOT IN THE "CRAMPED" POSITION, THE SPARK TIMING WILL BE FIXED BETWEEN 6 TO 10 DEGREES. USE THE POWER STEERING PRESSURE SWITCH FUNCTIONAL CHECK CHART IN SECTION 6E3-C ECM AND SENSORS.

THE FOLLOWING IS ADDITIONAL INFORMATION TO BE ADDED TO SECTION C4 IGNITION SYSTEM/EST OF THE SAME SERVICE MANUAL. UNDER THE HEADING "OPERATIONS," ADD THE FOLLOWING INFORMATION:

THE ECM CAN ALTER THE EST SPARK TIMING FOR SEVERAL REASONS. THE FOLLOWING ARE SOME OF THE REASONS FOR ALTERING THE EST ADVANCE: * THE POWER STEERING PRESSURE SWITCH INDICATES "HIGH PRESSURE." * IF BATTERY VOLTAGE IS LESS THAN 12 VOLTS, SPARK TIMING WILL APPEAR TO BE ADVANCED. THIS IS BECAUSE THE ECM-CONTROLLED DWELL HAS CHANGED TO ALLOW THE IGNITION COIL TO BE ABLE TO PRODUCE ENOUGH VOLTAGE TO CAUSE THE SPARK PLUGS TO FUNCTION PROPERLY.

THE ECM WILL RESUME NORMAL EST CONTROL IF NONE OF THE ABOVE CONDITIONS CONTINUED TO EXIST. COMPARING THE TECH 1 SCAN TOOL TYPICAL DATA VALUES WILL INDICATE BOTH BATTERY VOLTAGE AND THE STATE OF THE POWER STEERING PRESSURE SWITCH.

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.