SERVICE MANUAL UPDATE-SEC. 9JA REPLACEMENT PGS. FOR SIR CODES

Subject: SUPPLEMENTAL INFLATABLE RESTRAINT (SIR) CODES 23, 24, 34 AND 51 REPLACEMENT PAGES

Model and Year: 1990-91 GEO METRO CONVERTIBLE

The replacement pages contained within this bulletin replace and supersede Code 23, Code 24, Code 34 and Code 51 in Supplemental inflatable Restraint (SIR) System Diagnosis (Section 9J-A) of the 1990 Geo Metro Service Manual Supplement covering the Metro convertible model (ST370-90SUPP) and the 1991 Geo Metro Service Manual (ST370-91). Please refer to these pages whenever diagnosing SIR system Codes 23, 24, 34 and/or 51.

STEERING COLUMN CIRCUIT VOLTAGE TOO HIGH

Circuit Description:

Code 23 is set when the voltage at the -Sense Low" input, terminal "A6", is greater than a specific percentage of "36 VLR" output voltage for 500 milliseconds during the "Continuous Monitoring Tests" performed by the DERM. The "Continuous Monitoring Tests" are performed by the DERM after the initial "Turn-ON Tests" are completed and are performed every 100 milliseconds while "Ignition 1" voltage is present at the DERM. The Continuous Monitoring Tests" check the continuity of the deployment loop from the "36 VLR" output of the DERM through the arming sensor, inflator module and the discriminating sensors to ground. Code 23 indicates a shorted arming sensor, short to the "36 VLR," or an open ground to the deployment loop.

Test Conditions:

Tested every 100 milliseconds during the "Continuous Monitoring Tests."

Failure Conditions:

Code 23 will set if the voltage at the "Sense Low" input, terminal "A6", is greater than a specific percentage of "36 VLR" output voltage for 500 milliseconds.

Action Taken: . The DERM illuminates the "INFL REST" indicator.

Conditions to Clear: Current Code 23 will clear when the voltage at the "Sense Low" input, terminal "A6", is within a specific range of "36 VLR" output voltage for 500 milliseconds (five "Continuous Monitoring Tests" cycles) after a Code 23 has been set.

Test Description:

Number(s) below refer to circled number(s) on the diagnostic chart. 1. This test checks for a short from the "36 VLR" CKT 236 to the "Force High" CKT 714. 2. This test checks for a short from the "36 VLR" CKT 236 to the "Sense Low" CKT 752. 3. This test checks for a short from the "36 VLR" CKT 236 to the "Force Low" CKT 688. 4. This test checks for a short from the "36 VLR" CKT 236 to CKT 347. 5. This test checks for a short from the "36 VLR" CKT 236 to CKT 348. 6. This test determines whether the fault is due to a faulty arming sensor or a faulty DERM.

STEERING COLUMN CIRCUIT VOLTAGE TOO LOW

Circuit Description:

Code 24 is set when the voltage at the "Sense Low" input, terminal "A6", is within a specific range of "36 VLR" output voltage for 500 milliseconds during the "Continuous Monitoring Tests" performed by the DERM. The 'Continuous Monitoring Tests" are performed by the DERM after the initial "Turn-ON Tests" are completed and are performed every 100 milliseconds while "Ignition 1" voltage is present at the DERM. The "Continuous Monitoring Tests" check the continuity of the deployment loop from the "36 VLR" output of the DERM through the arming sensor, inflator module and the discriminating sensors to ground. Code 24 will set if the arming sensor resistance is too high or open, a discriminating sensor is shorted or resistance is too low, the "Force High," "Sense Low" or "Force Low" circuit is shorted to ground or system voltage, or the -Sense High" circuit is shorted to ground.

Test Conditions:

Tested every 100 milliseconds during the "Continuous Monitoring Tests."

Failure Conditions:

Code 24 will set if the voltage at the "Sense Low" input, terminal "A6", is within a specific range of "36 VLR" output voltage for 500 milliseconds.

Action Taken:

The DERM will illuminate the "INFL REST" indicator.

Conditions to Clear: Code 24 will clear if the voltage at the "Sense Low" input, terminal "A6", is within a specific range of "36 VLR" output voltage for 500 milliseconds.

Test Description:

Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test determines whether the fault is in the steering column or the diagnostic circuitry. 2. This test checks for a short from CKT 39 to CKT 347. 3. This test checks the integrity of the "Sense Low" 2490 ohm resistor and associated circuitry in the resistor module. 4. This test checks for an open in the "Sense Low" CKT 752. 5. This test determines whether the steering column fault is due to a faulty SIR coil assembly or a faulty inflator module. 6. This test checks for a short to ground in CKT 347. 7. This test checks for a short to ground in CKT 348. 8. This test checks for a short to ground in the "Force Low" CKT 688. 9. This test checks for a short to ground in the "Force High" CKT 714. 10. This test checks for a short to ground in the "Sense Low" CKT 752. 11. This test checks for a short to ground in the "Sense High" CKT 753. 12. This test checks for a faulty forward discriminating sensor. 13. This test determines whether the fault is due to a faulty passenger compartment discriminating sensor or a faulty DERM. 14. This test checks for a short to B + in CKT 347. 15. This test checks for a short to B + in CKT 348. 16. This test checks for a short to B + in the "Force Low"CKT 688. 17. This test checks for a short to B + in the "Force High" CKT 714. 18. This test checks for a short to B + in the "Sense Low" CKT 752. 19. This test checks for an open in CKT 347A. 20. This test checks for a faulty forward discriminating sensor. 21. This test checks for a faulty passenger compartment discriminating sensor. 22. This test determines whether the fault is due to a faulty arming sensor or a faulty DERM.

Circuit Description:

During the "Turn-ON Tests," the DERM monitors the voltage at the "Sense Low" input, terminal "A6", for 500 milliseconds. The DERM expects the voltage to be within a specific range of "Ignition 1" voltage before the "36 VLR" output is charged. If the "Ignition 1" circuit from the IG Fuse to the arming sensor (CKTs 39E, 39F and 39G) is open, the voltage at the "Sense Low" input, terminal "A6", will be less than a certain percentage of "Ignition 1" voltage and Code 34 will be set.

Test Conditions:

Tested once during each ignition cycle during the "Turn-ON Tests."

Failure Conditions:

Code 34 will set if the voltage at the "Sense Low" input, terminal "A6", is less than a certain percentage of "Ignition 1" voltage for 500 milliseconds and "36 VLR' voltage is less than "Ignition 1" voltage during the "Turn- ON Tests. "

Action Taken:

The DERM illuminates the "INFL REST" indicator.

Conditions to Clear: To clear Current Code 34, the ignition switch must be in "LOCK" long enough to ensure that the "36 VLR" supply voltage has fully discharged (about ten minutes). Once the "36 VLR" supply voltage is discharged, the DERM will again check the failure conditions when the ignition switch is turned to "ON." If the failure conditions are not present (no failure indicated) then, and only then, will Current Code 34 be cleared.

Test Description:

Number(s) below refer to circled number(s) on the diagnostic chart.

1 . This test checks to see if the DERM set the code falsely. 2. This test determines whether the fault is due to an open in the "Ignition 1" CKTs 39E, 39F and 39G or a faulty arming sensor.

Circuit Description:

The DERM determines that the arming sensor is closed when a specific percentage of deployment loop voltage or more is present at the "Sense High" input, terminal "A7", and it determines that a discriminating sensor is closed when a specific percentage of deployment loop voltage or less is present at the "Sense Low" input, terminal "A6'. If both conditions are detected simultaneously, Code 51 will set.

Test Conditions:

Code 51 conditions are monitored whenever the DERM is functioning properly.

Failure Conditions:

Current Code 51 will set if the DERM senses that both the arming sensor and at least one of the discriminating sensors are closed.

Action Taken:

The DERM illuminates the "INFL REST" indicator until Current Code 51 is cleared. When a History Code 51 is present, the DERM will not illuminate the "INFL REST" indicator.

Conditions to Clear: Current Code 51 can be cleared using a TECH 1 "Clear Codes" command. History Code 51 will remain in the DERM thereafter.

Test Description:

Number(s) below refer to circled number(s) on the diagnostic chart.

1. Code 51, once detected, can be erased as a Current Code, but will remain as an unerasable History Code 51. 2. If the inflator module has not deployed, Code 51 may have been set falsely. 3. If Code 51 is current with no signs of a frontal crash, it was set falsely. 4. This test checks to see if the DERM set the Code 51 falsely. 5. This test checks to see if the Code 51 was set inadvertently during SIR system diagnosis. 6. When a frontal crash has occurred, it is necessary to perform the indicated procedures and clear SIR codes to ensure that the SIR system is fully functional.

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.