Air Bag Restraint System Chevrolet Corvette C4

Scheme 1

DIAGNOSIS & TESTING

Note. After component replacement, perform a system operational check to ensure proper system operation. See TESTING - SYSTEM OPERATION CHECK .

Trouble Codes

Diagnostic Energy Reserve Module (DERM) provides a record of trouble codes stored according to type. Current codes are faults presently being detected. Current codes are stored in Random Access Memory (RAM) and are erased when fault is corrected.

Current codes can be read by using flash code diagnostics provided through INFLATABLE RESTRAINT indicator light, a Scan tester such as Tech 1 or on-board diagnostics on vehicles with an on-board diagnostics panel.

Flash Code Diagnostics

Flash code diagnostics can only be used to read current codes and determine if history codes are present. Flash code diagnostics cannot be used to clear codes or read history codes. Flash code diagnosis is enabled by grounding terminal "K" of Assembly Line Diagnostic Link (ALDL) connector, located under instrument panel, with ignition switch in ON position. Grounding terminal "K" signals Diagnostic Energy Reserve Module (DERM) to enter flash code diagnostic display mode.

DERM identifies 2-digit trouble codes by activating INFLATABLE RESTRAINT indicator via a lamp driver at SIR indicator low output. Each code displayed will consist of a number of flashes representing tens for first digit and a 1/2 second pause followed by a number of flashes representing ones for second digit of code. Each code is flashed once before moving on to next code. After all codes have been displayed, entire code sequence will continuously repeat until ground is removed from terminal "K" of ALDL connector.

Two special codes (Codes 12 and 13) exist when reading flash code mode. Code 12 will always be first code displayed when flash code mode is entered. Code 12 does not indicate a fault; it indicates flash code mode has been enabled. If there are no current or history codes present, DERM will display Code 12 until ground is removed from ALDL connector at terminal "K". Code 13 will be displayed if history codes are present. To read history codes, a Scan tester must be used.

Scan Tester Diagnostics

Scan tester must be used along with Inflator Module Load Tool (J-37808). A Scan tester will read and clear current codes and history codes. Ensure Scan tester contains correct cartridge for SIR diagnostics.

To use Scan tester, connect it to ALDL connector, plug in power source and turn ignition switch to ON position. Follow Scan tester manufacturer's instructions for communication with SIR system. Scan tester reads serial data from DERM data link output to ALDL connector.

On-Board Diagnostics

On-board diagnostics can only be utilized on vehicles with an on-board diagnostics panel. (Scheme 2) Diagnostics is entered by depressing WARM and OFF buttons on on-board diagnostics panel. (Scheme 3) Service mode and codes will appear in display area. Current Code 51 (accident detected) cannot be cleared with on-board diagnostics. A Scan tester is necessary to clear current Code 51. Current Code 34 will remain current after fault is repaired unless ignition if off long enough to allow 36-Volt Loop Reserve (36VLR) to fully discharge.

Scheme 2

Scheme 3

Note. Failure to follow correct diagnostic procedures may result in extended diagnostic time and incorrect diagnosis and parts replacement.

Diagnostic Procedure

1. SIR SYSTEM DIAGNOSTIC CHECK should always be starting point of SIR diagnostics. See «SIR DIAGNOSTIC SYSTEM CHECK»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system) under DIAGNOSTIC CHARTS. SIR DIAGNOSTIC SYSTEM CHECK checks for proper INFLATABLE RESTRAINT indicator light operation and SIR trouble codes using Flash Code and Scan tool methods.
2. SIR DIAGNOSTIC SYSTEM CHECK will lead to correct diagnostic chart to diagnose SIR problems. Always perform SIR DIAGNOSTIC SYSTEM CHECK after repair or diagnostic procedures to ensure repair is correct and no other problems are present.

Description

Diagnostic procedures used in this section are designed to find and repair SIR problems. For best results, utilize diagnostic charts, and follow sequence listed below

1. Perform SIR DIAGNOSTIC SYSTEM CHECK. SIR DIAGNOSTIC SYSTEM CHECK should be start of any SIR diagnosis. SIR DIAGNOSTIC SYSTEM CHECK checks for proper INFLATABLE RESTRAINT indicator operation, ability of Diagnostic Energy Reserve Module (DERM) to communicate through serial data line and whether SIR trouble codes are present.
2. Refer to diagnostic chart as directed by SIR DIAGNOSTIC SYSTEM CHECK. SIR DIAGNOSTIC SYSTEM CHECK will lead to correct chart to diagnose any SIR problems. By-passing these procedures may result in extended diagnostic time.
3. Repeat SIR DIAGNOSTIC SYSTEM CHECK after any repair or diagnostic procedures are performed. Repeating SIR DIAGNOSTIC SYSTEM CHECK will ensure repair was made correctly and no other conditions exist. When ignition is first turned on, system voltage is applied through SIR fuse to DERM at IGNITION 1 input terminals A3 and B3 and from instrument cluster fuse to DERM at SIR INDICATOR HIGH input. DERM responds by flashing INFLATABLE RESTRAINT indicator 7-9 times while performing tests on SIR system. When engine is cranked, system voltage is applied from CRANK-A/B fuse to DERM at CRANK input. DERM grounds SIR INDICATOR LOW output until system voltage is removed from CRANK input. This results in INFLATABLE RESTRAINT indicator remaining on during cranking. After engine is cranked, DERM will again flash INFLATABLE RESTRAINT indicator 7-9 times and perform tests on SIR system. NOTE: Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see «WIRING DIAGRAMS»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system) .
4. INFLATABLE RESTRAINT indicator should blink 7-9 times as ignition is turned on.
5. INFLATABLE RESTRAINT indicator should remain on steady during cranking.
6. After engine is cranked, INFLATABLE RESTRAINT indicator should flash 7-9 times, then go off.
7. INFLATABLE RESTRAINT warning light has successfully completed bulb check.
8. This test checks for proper operation of SERIAL DATA circuit and determines which history codes (if any) are stored.
9. Incorrect operation of INFLATABLE RESTRAINT indicator is indicated. This test differentiates a indicator light stays on condition from a indicator light does not come on condition.
10. This test differentiates a current fault codes exist condition from a diagnostics enabled when not requested condition.
11. INFLATABLE RESTRAINT indicator has completed bulb check and indicates current fault codes exist.
12. This test checks for proper operation of serial data circuit. This test also indicates which fault codes are stored and whether codes are current or history.

Scheme 4

When system voltage is applied, Diagnostic Energy Reserve Module (DERM) will perform TURN ON tests followed by CONTINUOUS MONITORING tests. If no faults are detected, DERM will perform a STEERING COLUMN RESISTANCE test. When a fault is detected, DERM will store a current code and illuminate INFLATABLE RESTRAINT indicator light. DERM will clear current codes (except for Code 51) when fault is no longer detected or when ignition switch is cycled. Code will then be stored as a history code until cleared with a Tech 1 Scan tool.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. DERM has detected an event in which SENSE HIGH input voltage was a certain percentage or more of deployment loop voltage and SENSE LOW voltage was simultaneously a certain percentage or less of deployment loop voltage.
2. Checks for intermittent electrical conditions within steering column.
3. Checks for intermittent shorts in 36-Volt Loop Reserve (VLR) wiring (circuit No. 236).
4. Checks for improperly installed INFLATABLE RESTRAINT bulb or uncleared Code 61 after a completed wiring repair on circuit No. 139. Also checks for intermittent faults in circuits No. 688 and 358.
5. Checks for intermittent opens in ground path of deployment loop between base of steering column and both discriminating sensors.
6. Checks for intermittent wiring shorts between 36-volt circuit No. 236 and circuits No. 347, 348 and 349 of SIR wiring harness.

Scheme 5

When system voltage is applied, Diagnostic Energy Reserve Module (DERM) will perform TURN-ON tests followed by CONTINUOUS MONITORING tests. If no faults are detected, DERM will perform STEERING COLUMN RESISTANCE test. When a fault is detected, DERM will store a current code and illuminate INFLATABLE RESTRAINT indicator light. DERM will clear current codes (except Code 51) when fault is no longer detected or when ignition switch is cycled. Code will then be stored as a history code until cleared with a Tech 1 Scan tool.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks for intermittent shorts to system voltage in 36-Volt Loop Reserve (36VLR) wiring (circuit No. 236).
2. Checks for intermittent shorts to ground in 36VLR wiring (circuit No. 236).
3. Checks for intermittent open in 36VLR wiring (circuit No. 236).
4. Checks for intermittent open in FORCE HIGH and FORCE LOW wiring (circuits No. 714 and 688).
5. Checks for intermittent opens or shorts to ground in SENSE LOW wiring (circuit No. 752).
6. Checks for shorts to system voltage in deployment loop (circuits No. 347, 348 and 349) or in diagnostic circuits (circuits No. 347, 348, 688, 714, 752 and 753).
7. Checks for shorts between circuit No. 236 and 347, 348 or 349.

Scheme 6

When system voltage is applied, Diagnostic Energy Reserve Module (DERM) will perform TURN-ON tests followed by CONTINUOUS MONITORING tests. If no faults are detected, DERM will perform a STEERING COLUMN RESISTANCE test. When a fault is detected, DERM will store a current code and illuminate INFLATABLE RESTRAINT indicator light. DERM will clear current codes (except Code 51) when fault is no longer detected or when ignition switch is cycled. Code will then be stored as a history code until cleared with a Tech 1 Scan tool.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks for intermittent opens on 36-Volt Loop Reserve (36VLR) wiring (circuit No. 236).
2. Checks for intermittent open between SIR fuse and arming sensor (circuit No. 1139).

Scheme 7

When ignition is first turned on, system voltage is applied from CLUSTER fuse to SIR INDICATOR HIGH and INFLATABLE RESTRAINT indicator light, which is connected to SIR INDICATOR LOW. SIR fuse also applies system voltage to IGNITION 1 inputs A3 and B3. Diagnostic Energy Reserve Module (DERM) responds by flashing INFLATABLE RESTRAINT indicator 7-9 times.

When engine is cranked, system voltage is applied to DERM at CRANK input. DERM grounds light circuit until system voltage is removed from CRANK input. This results in a steady INFLATABLE RESTRAINT indicator during cranking. After engine is cranked, DERM will again flash INFLATABLE RESTRAINT indicator 7-9 times.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. This test determines whether FLASH CODE diagnosis can be enabled.
2. This test checks for a good ground at Assembly Line Data Link (ALDL) connector.
3. This test checks for an open in DIAGNOSTIC REQUEST circuit.
4. This test checks for a short to battery positive voltage in DIAGNOSTIC REQUEST circuit.
5. This test determines whether further diagnosis is necessary.
6. This test determines whether only history or both current and history codes exist.

Scheme 8

When ignition is first turned on, system voltage is applied from CLUSTER fuse to SIR INDICATOR HIGH (terminal B9) and to INFLATABLE RESTRAINT indicator light, which is connected to SIR INDICATOR LOW (terminal A1). SIR fuse applies system voltage to IGNITION 1 inputs (terminals A3 and B3). Diagnostic Energy Reserve Module (DERM) responds by flashing INFLATABLE RESTRAINT indicator 7-9 times.

When engine is cranked, system voltage is applied from CRANK-A/B fuse to DERM at CRANK input. DERM grounds light circuit until system voltage is removed from CRANK input. This results in a steady INFLATABLE RESTRAINT indicator during cranking. After engine is cranked, DERM will again flash INFLATABLE RESTRAINT indicator 7-9 times.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. An open SIR fuse will cause INFLATABLE RESTRAINT indicator light to come on steady and an Engine Cranks But Will Not Run condition.
2. A disconnected DERM harness connector will cause indicator light to come on steady via shorting bar from terminal A1 to terminal B1.
3. Checks for a faulty shorting bar on DERM harness connector.
4. Checks for a short from SIR INDICATOR LOW circuit to ground.
5. Checks for an open in IGNITION 1 circuitry to DERM.
6. Checks for a short from CRANK input circuit to battery positive voltage.
7. Checks whether a short to ground caused SIR fuse to open.

Scheme 9

When ignition is first turned on, system voltage is applied from CLUSTER fuse to SIR INDICATOR HIGH (terminal B9) and INFLATABLE RESTRAINT indicator light, which is connected to SIR INDICATOR LOW (terminal A1). SIR fuse applies system voltage to IGNITION 1 inputs A3 and B3. Diagnostic Energy Reserve Module (DERM) responds by flashing INFLATABLE RESTRAINT indicator 7-9 times.

When engine is cranked, system voltage is applied from CRANK-A/B fuse to DERM at CRANK input. DERM grounds light circuit until system voltage is removed from CRANK input. This results in a steady INFLATABLE RESTRAINT indicator during cranking. After engine is cranked, DERM will again flash INFLATABLE RESTRAINT indicator 7-9 times.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks if fault is in DERM circuitry or in Driver Information Center (DIC) display circuitry.
2. Checks if fault is in DERM half of circuit or in DIC half of circuit.
3. Checks for a short from SIR INDICATOR LOW circuit to positive battery voltage.
4. Checks whether fault is due to a bad bulb.
5. Checks for an open in SIR INDICATOR LOW circuit.
6. Checks for an open in SIR INDICATOR LOW circuit.
7. Checks for a good ground to DERM. If ground is good, fault is a faulty DERM.

Scheme 10

When ignition is first turned on, system voltage is applied from CLUSTER fuse to SIR INDICATOR HIGH (terminal B9) and INFLATABLE RESTRAINT indicator light, which is connected to SIR INDICATOR LOW (terminal A1). SIR fuse applies system voltage to IGNITION 1 inputs A3 and B3. Diagnostic Energy Reserve Module (DERM) responds by flashing INFLATABLE RESTRAINT indicator 7-9 times.

When engine is cranked, system voltage is applied from CRANK-A/B fuse to DERM at CRANK input. DERM grounds light circuit until system voltage is removed from CRANK input. This results in a steady INFLATABLE RESTRAINT indicator during cranking. After engine is cranked, DERM will again flash INFLATABLE RESTRAINT indicator 7-9 times.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. 8) Checks whether power is available to Driver Information Center (DIC).
2. 9) Checks for an open in power feed circuit to DIC.
3. 10) Checks for improper power feed connections to DIC.
4. 11) Checks whether power is available to CLUSTER fuse.
5. 12) Checks for a short to ground causing CLUSTER fuse to open.

Scheme 11

When ignition is first turned on, system voltage is applied from CLUSTER fuse to SIR INDICATOR HIGH and INFLATABLE RESTRAINT indicator light, which is connected to SIR INDICATOR LOW. SIR fuse applies system voltage to IGNITION 1 inputs A3 and B3. Diagnostic Energy Reserve Module (DERM) responds by flashing INFLATABLE RESTRAINT indicator 7-9 times.

When engine is being cranked, system voltage is applied from CRANK-A/B fuse to DERM at CRANK input. DERM grounds light circuit until system voltage is removed from CRANK input. This results in a steady INFLATABLE RESTRAINT indicator during cranking. After engine is cranked, DERM will again flash INFLATABLE RESTRAINT indicator 7-9 times if ignition is on.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks whether fault is due to an open CRANK-A/B fuse.
2. Checks for a proper signal to CRANK input during cranking.
3. Determines whether lack of proper crank signal is due to an open CRANK input or an open power feed to CRANK-A/B fuse.
4. Checks whether CRANK-A/B fuse is open due to a short to ground in CRANK input circuit.
5. Test determines whether short to ground is in wiring harness or DERM.

Scheme 12

When ignition is first turned on, system voltage is applied from CLUSTER fuse to SIR INDICATOR HIGH and INFLATABLE RESTRAINT indicator light, which is connected to SIR INDICATOR LOW. SIR fuse applies system voltage to IGNITION 1 inputs A3 and B3. Diagnostic Energy Reserve Module (DERM) responds by flashing INFLATABLE RESTRAINT indicator 7-9 times.

When engine is being cranked, system voltage is applied from CRANK-A/B fuse to DERM at CRANK input. DERM grounds light circuit until system voltage is removed from CRANK input. This results in a steady INFLATABLE RESTRAINT indicator during cranking. After engine is cranked, DERM will again flash INFLATABLE RESTRAINT indicator 7-9 times if ignition is on.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

Checks for a short to ground on DIAGNOSTIC REQUEST (circuit No. 327) for voltage at Assembly Line Data Link (ALDL) connector terminal K. Since grounding of DIAGNOSTIC REQUEST circuit enables diagnostics (flashes Code 12), this ground must be supplied by DERM or wiring.

Scheme 13

When ignition is first turned on, system voltage is applied from CLUSTER fuse to SIR INDICATOR HIGH (terminal B9) and INFLATABLE RESTRAINT indicator light, which is connected to SIR INDICATOR LOW. SIR fuse applies system voltage to IGNITION 1 inputs A3 and B3. Diagnostic Energy Reserve Module (DERM) responds by flashing INFLATABLE RESTRAINT indicator 7-9 times.

When engine is being cranked, system voltage is applied from CRANK-A/B fuse to DERM at CRANK input. DERM grounds light circuit until system voltage is removed from CRANK input. This results in a steady INFLATABLE RESTRAINT indicator during cranking. After engine is cranked, DERM will again flash INFLATABLE RESTRAINT indicator 7-9 times if ignition switch is on.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. An improper connection to Assembly Line Data Link (ALDL) connector will prevent communications from being established.
2. Correct BODY SYSTEMS cartridge must be used.
3. Test checks for a functional CCM. Tech 1 Scan tool must establish communications with CCM before communication with DERM is allowed.
4. Checks for a short to ground on SERIAL DATA circuit.
5. Checks for an open in SERIAL DATA circuit.
6. Checks for a short to battery positive voltage on SERIAL DATA circuit.

Scheme 14

DERM injects a current through steering column from FORCE HIGH output (terminal A4) to FORCE LOW output (terminal A10). By monitoring voltage at SENSE HIGH input (terminal A7) and SENSE LOW input (terminal A6), DERM calculates combined resistance of inflator module, SIR coil, harness wiring (circuits No. 347 and 348) and terminal contact in steering column.

Test Conditions

Tested once each ignition cycle during STEERING COLUMN RESISTANCE test if

1. No faults are detected during TURN-ON.
2. No faults are detected during CONTINUOUS MONITORING for one second.
3. No crank signal is present.
4. IGNITION 1 voltage is present.

Failure Conditions

Code 21 will set if combined resistance of inflator module, SIR coil, harness wiring and connector terminal contact in steering column is greater than a specified value.

Conditions To Clear

Code 21 will clear each time ignition is turned off.

Action Taken

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks whether fault is in steering column or diagnostic circuitry.
2. Checks integrity of 430-ohm resistor and associated circuitry in resistor module.
3. Checks integrity of 49.9-ohm resistor, 100-ohm resistor and associated circuitry in resistor module.
4. Test checks integrity of two 2490-ohm resistors and associated circuitry in resistor module.
5. Test determines whether steering column fault is due to SIR coil or inflator module.

Scheme 15

DERM injects a current through steering column from FORCE HIGH output (terminal A4) to FORCE LOW output (terminal A10). By monitoring voltage at SENSE HIGH input (terminal A7) and SENSE LOW input (terminal A6), DERM calculates combined resistance of inflator module, SIR coil, harness wiring (circuits No. 347 and 348) and connector terminal contact in steering column.

Tested once each ignition cycle during STEERING COLUMN RESISTANCE test if

1. No faults are detected during TURN-ON.
2. No faults are detected during CONTINUOUS MONITORING for one second.
3. No crank signal is present.
4. IGNITION 1 voltage is present.

Code 21 will set if combined resistance of inflator module, SIR coil, harness wiring and connector terminal contact in steering column is greater than a specified value.

Code 21 will clear each time ignition is turned off.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. 6) Checks integrity of circuits No. 347B and 348B and wiring harness to SIR coil connection.
2. 7) Checks for a short from FORCE HIGH circuit to SENSE HIGH circuit.
3. 8) Checks for a short from SENSE HIGH circuit to battery positive voltage.
4. 9) Determines whether fault is in circuit No. 347B or 348B.

Scheme 16

DERM injects a current through steering column from FORCE HIGH output (terminal A4) to FORCE LOW output (terminal A10). By monitoring voltage at SENSE HIGH input (terminal A7) and SENSE LOW input (terminal A6), DERM calculates combined resistance of inflator module, SIR coil, harness wiring (circuits No. 347 and 348) and connector terminal contact in steering column. Code 22 will set if combined resistance of inflator module, SIR coil, harness wiring and connector terminal contact in steering column is less than a specified value.

Tested once each ignition cycle during STEERING COLUMN RESISTANCE test if

1. No faults are detected during TURN-ON.
2. No faults are detected during CONTINUOUS MONITORING for one second.
3. No crank signal is present.
4. IGNITION 1 voltage is present.

Code 22 will set if combined resistance of inflator module, SIR coil, harness wiring and connector terminal contact in steering column is less than a specified value.

Code 22 will clear each time ignition is turned off.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks if fault is in steering column or diagnostic circuitry.
2. Checks integrity of 430-ohm resistor and associated circuitry in resistor module.
3. Checks integrity of 49.9-ohm resistor, 100-ohm resistor and associated circuitry in resistor module.
4. Checks integrity of two 2490-ohm resistors and associated circuitry in resistor module.
5. Determines whether steering column fault is due to SIR coil or inflator module.

Scheme 17

DERM injects a current through steering column from FORCE HIGH output (terminal A4) to FORCE LOW output (terminal A10). By monitoring voltage at SENSE HIGH input (terminal A7) and SENSE LOW input (terminal A6), DERM calculates combined resistance of inflator module, SIR coil, harness wiring (circuits No. 347 and 348) and connector terminal contact in steering column. Code 22 will set if combined resistance of inflator module, SIR coil, harness wiring and connector terminal contact in steering column is less than a specified value.

Tested once each ignition cycle during STEERING COLUMN RESISTANCE test if

1. No faults are detected during TURN-ON.
2. No faults are detected during CONTINUOUS MONITORING for one second.
3. No crank signal is present.
4. IGNITION 1 voltage is present.

Code 22 will set if combined resistance of inflator module, SIR coil, harness wiring and connector terminal contact in steering column is less than a specified value.

Code 22 will clear each time ignition is turned off.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. 6) Checks for a short from circuit No. 347 to 348.
2. 7) Checks for an open in SENSE HIGH circuit.
3. 8) Checks for a short from SENSE HIGH circuit to FORCE LOW circuit.
4. 9) Checks for a short from SENSE LOW circuit to FORCE HIGH circuit.
5. 10) Checks for a short from SENSE LOW circuit to SENSE HIGH circuit.

Scheme 18

DERM injects a current through steering column from FORCE HIGH output (terminal A4) to FORCE LOW output (terminal A10). By monitoring voltage at SENSE HIGH input (terminal A7) and SENSE LOW input (terminal A6), DERM calculates combined resistance of inflator module, SIR coil, circuits No. 347 and 348, and connector terminal contact in steering column. Codes 22 and 21 will set if voltage at SENSE LOW input (terminal A6) is less than a certain voltage during STEERING COLUMN RESISTANCE test. This results in an undetermined steering column resistance.

Tested once each ignition cycle during STEERING COLUMN RESISTANCE test if

1. No faults are detected during TURN-ON.
2. No faults are detected during CONTINUOUS MONITORING for one second.
3. No crank signal is present.
4. IGNITION 1 voltage is present.

Codes 21 and 22 will set if voltage at SENSE LOW input (terminal A6) is less than a certain voltage during first portion of STEERING COLUMN RESISTANCE test. This results in an undetermined steering column resistance.

Current Codes 21 and 22 will be cleared each time ignition is turned off.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks integrity of 49.9-ohm resistor, 100-ohm resistor, 430-ohm resistor and associated circuitry in resistor module.
2. Checks integrity of two 2490-ohm resistors and associated circuitry in resistor module.
3. Checks for an open in FORCE HIGH resistor circuitry in resistor module.
4. Checks for a short from circuits No. 348 or 349 to FORCE LOW circuit.
5. Checks for an open in FORCE HIGH circuit.
6. Checks for short from FORCE LOW circuit to SENSE LOW circuit.

Scheme 19

Code 23 is set when voltage at SENSE LOW input (terminal A6) is greater than a specific percentage of 36VLR for 500 milliseconds during CONTINUOUS MONITORING tests performed by DERM. CONTINUOUS MONITORING tests are performed by DERM after initial TURN-ON tests are completed and every 100 milliseconds while IGNITION 1 voltage is present at DERM. CONTINUOUS MONITORING tests check continuity of deployment loop from 36VLR output of DERM through arming sensor, inflator module and discriminating sensors to ground. Code 23 indicates a shorted arming sensor, short to 36VLR or an open ground to deployment loop.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 23 will set if voltage at SENSE LOW input (terminal A6) is greater than a specific percentage of 36-Volt Loop Reserve (36VLR) output voltage for 500 milliseconds during CONTINUOUS MONITORING tests performed by Diagnostic Energy Reserve Module (DERM).

Current Code 23 will clear if voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR output voltage for 500 milliseconds (5 consecutive CONTINUOUS MONITORING cycles) after Code 23 has been set.

DERM turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks integrity of low side of deployment loop.
2. Checks for proper resistance of arming sensor.
3. Checks for a short from 36VLR circuit to FORCE HIGH circuit.
4. Checks for a short from 36VLR circuit to SENSE LOW circuit.
5. Checks for a short from 36VLR circuit to circuit No. 347.
6. Checks for a short from 36VLR circuit to circuit No. 348 or 349.
7. Determines whether fault is in circuit No. 348A or ground circuit.

Scheme 20

Code 24 is set when voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR for 500 milliseconds during CONTINUOUS MONITORING tests performed by DERM. CONTINUOUS MONITORING tests are performed by DERM after initial TURN-ON tests are completed and every 100 milliseconds while IGNITION 1 voltage is present at DERM. CONTINUOUS MONITORING tests check continuity of deployment loop from 36VLR of DERM through arming sensor, inflator module and discriminating sensors to ground.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 24 will set if voltage at SENSE LOW input is within a specific range of 36-Volt Loop Reserve (36VLR) output for 500 milliseconds.

Code 24 will clear if voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR output voltage for 500 milliseconds.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Determines if fault is in steering column of diagnostic circuitry.
2. Checks integrity of IGNITION 1 feed to high side of deployment loop.
3. Checks integrity of SENSE LOW 2490-ohm resistor and associated circuitry in resistor module.
4. Checks for open in SENSE LOW circuit.
5. Determines whether steering column fault is due to SIR coil or inflator module.

Scheme 21

Code 24 is set when voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR for 500 milliseconds during CONTINUOUS MONITORING tests performed by DERM. CONTINUOUS MONITORING tests are performed by DERM after initial TURN-ON tests are completed and every 100 milliseconds while IGNITION 1 voltage is present at DERM. CONTINUOUS MONITORING tests check continuity of deployment loop from 36VLR of DERM through arming sensor, inflator module and discriminating sensors to ground. Code 24 will set if arming sensor resistance is too high or open, if discriminating sensor resistance is too low or shorted, if FORCE HIGH, SENSE LOW or FORCE LOW circuits are shorted to ground or system voltage or if SENSE HIGH circuit is shorted to ground.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 24 will set if voltage at SENSE LOW input is within a specific range of 36-Volt Loop Reserve (36VLR) output for 500 milliseconds.

Code 24 will clear if voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR for 500 milliseconds.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. 6) Checks for an open in circuit No. 347.
2. 7) Checks for a short from circuit No. 347 to ground.
3. 8) Checks for a short from circuit No. 348 or 349 to ground.
4. 9) Checks for a short from FORCE LOW circuit to ground.
5. 10) Checks for a short from FORCE HIGH circuit to ground.
6. 11) Checks for a short from SENSE LOW circuit to ground.
7. 12) Checks for a short from SENSE HIGH circuit to ground.
8. 13) Checks for proper resistance of each forward discriminating sensor.

Scheme 22

Code 24 is set when voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR for 500 milliseconds during CONTINUOUS MONITORING tests performed by DERM. CONTINUOUS MONITORING tests are performed by DERM after initial TURN-ON tests are completed and every 100 milliseconds while IGNITION 1 voltage is present at DERM. CONTINUOUS MONITORING tests check continuity of deployment loop from 36VLR of DERM through arming sensor, inflator module and discriminating sensors to ground. Code 24 will set if arming sensor resistance is too high or open, if discriminating sensor resistance is too low or shorted, if FORCE HIGH, SENSE LOW or FORCE LOW circuits are shorted to ground or system voltage or if SENSE HIGH circuit is shorted to ground.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 24 will set if voltage at SENSE LOW input is within a specific range of 36-Volt Loop Reserve (36VLR) output for 500 milliseconds.

Code 24 will clear if voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR for 500 milliseconds.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. 14) Checks for a short from circuit No. 347 to battery positive voltage.
2. 15) Checks for a short from circuit No. 348 or 349 to battery positive voltage.
3. 16) Checks for a short from FORCE LOW circuit to battery positive voltage.
4. 17) Checks for a short from FORCE HIGH circuit to battery positive voltage.
5. 18) Checks for a short from SENSE LOW circuit to battery positive voltage.
6. 19) Checks for proper resistance of each forward discriminating sensor.

Scheme 23

DERM grounds FORCE LOW output (terminal A10) and then monitors voltage at SENSE LOW input (terminal A6). If voltage at SENSE LOW input is within a specific range of IGNITION 1, Code 25 will set. Code 25 indicates a short to battery voltage on steering column or in circuit No. 347, 348 or 349. Code 25 can also be set if actual resistance of 100-ohm resistor within resistor module is too high or is open.

Tested once each ignition cycle during STEERING COLUMN RESISTANCE test if

1. No faults are detected during TURN-ON.
2. No faults are detected during CONTINUOUS MONITORING for one second.
3. No crank signal is present.
4. IGNITION 1 voltage is present.

Code 25 will set if voltage at SENSE LOW input (terminal A6) is within a specific range of IGNITION 1 voltage during first portion of STEERING COLUMN RESISTANCE test.

Current Code 25 will be cleared each time ignition is turned off.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Test removes steering column from system. If Code 25 is still current, problem is not in steering system.
2. Checks for a short to voltage in circuit No. 347.
3. Checks for a short to voltage in circuit No. 348 or 349.
4. Checks for a short to voltage in FORCE LOW circuit.
5. Checks for proper resistance of 100-ohm resistor in resistor module.
6. Because steering column is setting this code, replace inflator module or SIR coil. Repair condition in steering column which caused damage to component or wires to avoid damage to new component.

Scheme 24

If there is an open in SIR coil, inflator module or wiring in steering column, resistance between SENSE HIGH input (terminal A7) and SENSE LOW input (terminal A6) increases. This increased resistance causes a larger voltage drop from SENSE HIGH input to SENSE LOW input across 430-ohm resistor in resistor module. Increase in voltage between SENSE HIGH input and SENSE LOW input is sensed by DERM during CONTINUOUS MONITORING test, and Code 26 is set.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 26 will set if voltage at SENSE HIGH input (terminal A7) minus voltage at SENSE LOW input (terminal A6) is greater than a certain voltage for 500 milliseconds.

Current Code 26 will clear if voltage at SENSE HIGH input (terminal A7) minus voltage at SENSE LOW input (terminal A6) is greater than zero volts but less than a certain voltage for 500 milliseconds after Code 26 has been set.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks if fault is in steering column or diagnostic circuitry.
2. Checks for an open between resistor module and steering column on high side of deployment loop.
3. Checks for an open between resistor module and steering column on low side of deployment loop.
4. Checks for a short from 36-Volt Loop Reserve (36VLR) circuit to SENSE HIGH circuit.
5. Test determines whether steering column fault is due to SIR coil or inflator module.

Scheme 25

Voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR output when 36VLR output of DERM is functional. Should circuit open between 36VLR output and arming sensor, IGNITION 1 voltage will supply deployment loop. Voltage at SENSE LOW input (terminal A6) will decrease due to lower supply voltage, and Code 31 will set after 700 milliseconds (if Code 42 is not set). Code 31 indicates an open in wiring between 36VLR output of DERM and arming sensor, an open diode in arming sensor or a problem with SENSE HIGH or SENSE LOW circuits.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 31 will set if voltage at SENSE LOW input is within a specific range or IGNITION 1 voltage for 700 milliseconds and Code 42 is not set.

Current Code 31 will clear if voltage at SENSE LOW input is within a specific range of 36-Volt Loop Reserve (36VLR) output for 500 milliseconds.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks for an open between arming sensor terminal B and its diagnostic resistor.
2. Checks for an open in circuit No. 236.

Scheme 26

Voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR output voltage when 36VLR of DERM is charged. Should circuit short to ground between 36VLR and diode B, IGNITION 1 voltage will supply deployment loop. Voltage at SENSE LOW input (terminal A6) will decrease due to decrease in supply voltage, and Code 32 will set after 700 milliseconds. Code 32 indicates a short to ground in wiring between 36VLR of DERM and arming sensor.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 32 will set if voltage at SENSE LOW input (terminal A6) is within a specific range of IGNITION 1 output voltage for 700 milliseconds or Code 42 is set.

Current Code 32 will clear if voltage at SENSE LOW input (terminal A6) is within a specific range of 36-Volt Loop Reserve (36VLR) output voltage for 500 milliseconds.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

Checks for a short from 36VLR circuit to ground.

Scheme 27

At TURN-ON, DERM monitors voltage at 36VLR output before this circuit begins to charge. If diode B in wiring harness to arming sensor connected to terminal B is shorted, IGNITION 1 voltage will be present at 36VLR output (terminal A2) as soon as ignition is turned on. If DERM detects this voltage 3 ignition cycles in a row, History Code 33 will be set.

Tested once during each ignition cycle at TURN-ON.

History Code 33 will set if voltage at 36-Volt Loop Reserve (36VLR) of Diagnostic Energy Reserve Module (DERM) is detected within first 500 milliseconds after ignition is turned on, 3 ignition cycles in a row.

History Code 33 will remain as a history code until codes are cleared with a Tech 1 Scan tool.

DERM stores a History Code 33.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks whether code was set by short ignition cycles.
2. Checks whether a Code 33 condition exists.
3. Checks whether fault is a short to voltage on 36VLR circuit or a shorted steering diode.

Scheme 28

At TURN-ON, DERM monitors voltage at SENSE LOW input (terminal A6) for 500 milliseconds. DERM expects voltage to be within a specific range of IGNITION 1 voltage before 36VLR output is charged. If IGNITION 1 circuit from splice to arming sensor is open, voltage at SENSE LOW input (terminal A6) will be less than a certain percentage of IGNITION 1 voltage, and Code 34 will set.

Tested once during each ignition cycle at TURN-ON.

Code 34 will set if voltage at SENSE LOW input (terminal A6) is less than a certain percentage of IGNITION 1 voltage for 500 milliseconds and 36-Volt Loop Reserve (36VLR) is less than IGNITION 1 voltage at TURN-ON.

To clear Code 34, ignition must be off long enough to ensure 36VLR supply voltage has fully discharged. Once 36VLR is discharged, Diagnostic Energy Reserve Module (DERM) will again check failure conditions upon key on. Only if failure conditions are not present (no failure indicated) will current Code 34 be cleared.

DERM turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks for a short to ground on high side of deployment loop.
2. Checks for an open between arming sensor and steering column.
3. Checks for proper resistance of arming sensor.
4. Checks whether IGNITION 1 voltage is available at arming sensor.

Scheme 29

Code 35 is set when voltage at SENSE LOW input (terminal A6) is within a specific range of 36VLR output voltage for 500 milliseconds during CONTINUOUS MONITORING tests performed by DERM. CONTINUOUS MONITORING tests are performed by DERM after initial TURN-ON tests are completed and every 100 milliseconds while IGNITION 1 voltage is present at DERM. If a discriminating sensor is open, voltage at SENSE LOW input will increase due to increase in resistance of discriminating sensor section of deployment loop, and Code 35 will set.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 35 will set if voltage at SENSE LOW input (terminal A6) is within a specific range of 36-Volt Loop Reserve (36VLR) output voltage for 500 milliseconds.

Current Code 35 will clear if voltage at SENSE LOW input is within a specific range of 36VLR output voltage for 500 milliseconds.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks resistance of left forward discriminating sensor.
2. Checks resistance of right forward discriminating sensor.
3. Checks for an open in circuit No. 349.
4. Checks for an open in ground circuit No. 1003E.

Scheme 30

DERM measures deployment loop energy reserve voltage (36VLR) and ensures it reaches a certain voltage within 7 seconds after IGNITION 1 voltage is applied to DERM. If this voltage is not reached, Code 41 is set. DERM monitors 36VLR and ensures it remains above a certain voltage while IGNITION 1 voltage is present. If 36VLR falls below a certain voltage after initial charging, Code 42 is set. These codes indicate a fault internal to DERM or a short to ground or voltage between diode B and 36VLR output terminal A2.

Code 41 is tested once during each ignition cycle when ignition is turned on. Code 42 is tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 41 will set if 36-Volt Loop Reserve (36VLR) has not reached a certain voltage 7 seconds after TURN-ON. Code 42 will set if 36VLR is below a certain voltage after initial charging.

Current Code 41 will be cleared each time ignition is turned off. Code 42 will set if 36VLR is below a certain voltage after initial charging.

Diagnostic Energy Reserve Module (DERM) turns on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Ensures IGNITION 1 feeds to DERM are spliced together.
2. Checks whether diode A is shorted.
3. Checks for a short from 36VLR circuit to voltage.

Scheme 31

DERM determines arming sensor is closed when system voltage or more is present at SENSE HIGH input and determines discriminating sensor is closed when low voltage is seen at SENSE LOW input.

Diagnostic Energy Reserve Module (DERM) energy reserve voltage is okay.

Current Code 51 will set if DERM senses arming sensor and at least one discriminating sensor are closed simultaneously.

Current Code 51 can be cleared using a Tech 1 Scan tool clear codes command. History Code 51 will remain in DERM thereafter.

DERM turns on INFLATABLE RESTRAINT indicator until Current Code 51 is cleared.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Code 51, once detected, can be erased as a current code but will remain as an unerasable history code.
2. If inflator module has not deployed, Code 51 may have set falsely.
3. If Code 51 is current with no signs of frontal impact, code has set falsely.
4. Checks for a DERM fault setting code falsely.
5. Checks whether code was set inadvertently during diagnosis.
6. If an accident has occurred, perform indicated procedures to ensure SIR system is functional.

Scheme 32

When there is a vehicle accident of sufficient magnitude to set a Code 51, DERM stores accident information in EEPROM. Code 52 is set when EEPROM has stored 4 simultaneously closed arming and discriminating sensor events (Code 51 settings).

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 52 will set when Electrically Erasable Programmable Read Only Memory (EEPROM) area reserved for accident data in Diagnostic Energy Reserve Module (DERM) is detected to be full during CONTINUOUS MONITORING.

Code cannot be cleared.

INFLATABLE RESTRAINT indicator is turned on during all future ignition cycles.

Scheme 33

DERM monitors ground driver output by comparing output state to processor commanded state. Code 61 will set when commanded state does not match output state of either ground driver at terminal A1 or A10. A possible cause for a Code 61 is an open in FORCE LOW circuit.

Tested every 100 milliseconds during CONTINUOUS MONITORING.

Code 61 will set if voltage at SENSE LOW input is greater than a certain voltage and feedback from ground driver (quad driver module) does not agree with commanded state for 500 milliseconds.

Current Code 61 will be cleared each time ignition is turned off.

Diagnostic Energy Reserve Module (DERM) attempts to turn on INFLATABLE RESTRAINT indicator light.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS .

1. Checks for proper resistance of 100-ohm resistor in resistor module.
2. Checks for an open in FORCE LOW circuit.

Scheme 34

Code 71 is an internal DERM fault and will set if any of these conditions are detected

1. DERM power supply reserve voltage charge or discharge time fails.
2. DERM power supply reserve voltage out of range for 500 milliseconds.
3. DERM is unable to read from or write to Electrically Erasable Programmable Read Only Memory (EEPROM).
4. The 36VLR is greater than a certain voltage for 500 milliseconds.

Tested during TURN-ON and every 100 milliseconds during CONTINUOUS MONITORING.

Code 71 is set when an internal Diagnostic Energy Reserve Module (DERM) fault is detected during TURN-ON or CONTINUOUS MONITORING.

Current Code 71 will clear if no internal DERM faults are detected for 500 milliseconds.

DERM turns on INFLATABLE RESTRAINT indicator light.

Scheme 35

DESCRIPTION & OPERATION

SUPPLEMENTAL INFLATABLE RESTRAINT (SIR) SYSTEM

The Supplemental Inflatable Restraint (SIR) system is designed to protect the driver in a frontal collision. The air bag will deploy only upon frontal or near frontal impact of no more than 30 degrees off the centerline of the vehicle. The system is not designed to deploy in rear impacts, side impacts or rollovers. A frontal impact of sufficient severity (comparable to a collision into a solid wall at approximately 14 MPH or more) will cause the sensors in the vehicle to detect this sudden deceleration. These sensors, in turn, trigger the inflator module.

DIAGNOSTIC ENERGY RESERVE MODULE (DERM)

The Diagnostic Energy Reserve Module (DERM) maintains a 36-Volt Loop Reserve (36VLR) energy supply to provide deployment energy for approximately 10-14 minutes if voltage is low or lost in an accident. In addition, the DERM performs diagnostic monitoring of all system components, stores both current and past SIR system fault code information, warns driver of SIR system faults by controlling INFLATABLE RESTRAINT indicator light and records SIR system status during a vehicle accident.

The DERM is connected to the SIR harness by a 24-pin connector. The harness connector uses gold-plated terminals and a gold-plated shorting bar in the contact area. The DERM connector also has a gold-plated shorting bar to connect INFLATABLE RESTRAINT indicator input to ground when the DERM connector is disconnected. With the DERM disconnected, the INFLATABLE RESTRAINT indicator remains on when ignition switch is turned to RUN or START positions. The DERM is located under the instrument panel.

INFLATABLE RESTRAINT INDICATOR LIGHT

When ignition switch is in RUN or START position, battery voltage is applied to the INFLATABLE RESTRAINT indicator light. The Diagnostic Energy Reserve Module (DERM) illuminates the light by providing a ground to a lamp driver. The INFLATABLE RESTRAINT indicator light verifies bulb and DERM operation by flashing 7-9 times when the ignition is first turned on, warning the driver of SIR electrical system faults which could potentially affect the operation of the SIR system. In addition, on vehicles without on-board diagnosis, the light provides diagnostic information by flashing fault codes when the flash code diagnostic mode is entered. The INFLATABLE RESTRAINT indicator light is the key to driver notification of SIR system faults.

ARMING SENSOR

The arming sensor is a protective switch located in the power feed side (positive side) of the deployment loop. It is calibrated to close at low-level velocity changes (lower than discriminating sensors). This ensures inflator module is connected directly to the 36-Volt Loop Reserve (36VLR) output of the Diagnostic Energy Reserve Module (DERM) and ignition voltage when either discriminating sensor closes.

The arming sensor consists of a sensing element, normally open switch contacts, a diagnostic resistor and 2 diodes. The sensing element closes the normally open switch contacts when the velocity of the vehicle changes at a rate indicating potential need for deployment. The diagnostic resistor is connected parallel with the normally open switch contacts and allows for a small amount of current flow through the deployment loop during normal non-deployment conditions. This small current flow results in voltage drops across each component within the loop.

The DERM monitors these voltage drops to detect circuit or component faults. The 2 diodes provide isolation between the 36VLR output of the DERM and ignition voltage. In some vehicles, the arming sensor is combined with the passenger compartment discriminating sensor. The arming sensor is located under the center of the instrument panel/console area of the vehicle.

DISCRIMINATING SENSORS

There are 2 discriminating sensors in the SIR system. Some vehicles have 2 forward discriminating sensors, while other vehicles have one forward discriminating sensor and a passenger compartment discriminating sensor. The forward discriminating sensor(s) is located on the radiator support brace. The passenger compartment discriminating sensor is located under the center of the instrument panel/console area or under the front passenger seat. In some vehicles, the passenger compartment discriminating sensor is combined with the arming sensor. Discriminating sensors are wired in parallel on the ground side of the deployment loop. These sensors are calibrated to close when deceleration velocity changes are severe enough to warrant deployment.

The sensors consist of a sensing element, normally open switch contacts and a diagnostic resistor. The sensing element closes the normally open switch contacts when the vehicle velocity changes are severe enough to warrant deployment.

A diagnostic resistor is connected parallel with the normally open switch contacts within each of the sensors. These parallel resistors supply the ground path for the current passing through the deployment loop during normal non-deployment conditions. This small current flow results in a voltage drop across each component within the loop. The DERM monitors these voltage drops to detect circuit or component faults.

SIR COIL ASSEMBLY

The SIR coil assembly consists of 2 current-carrying coils. It is installed in the steering column and allows rotation of the steering wheel while maintaining continuous (directly wired) contact of the deployment loop through the inflator module. The SIR system does not use slip rings to transmit current from the column to the steering wheel.

Gold-plated terminals and shorting bar are used on the coil assembly lower steering column Yellow connector. The shorting bar shorts the circuits to the main coil and inflator module when the lower steering column connector is disconnected. This shorts the circuit to the inflator module, preventing unwanted deployment of the air bag when servicing the steering column or other SIR components.

INFLATOR MODULE

When the vehicle is in an accident of sufficient force to simultaneously close the arming sensor and at least one discriminating sensor, nitrogen gas inflates the air bag packed inside the steering wheel hub. The air bag inflates and deploys in less than 1/20 of a second. As the driver contacts the air bag, the gas is vented and deflation occurs.

RESISTOR MODULE

The resistor module is located in the SIR harness between the inflator module and the Diagnostic Energy Reserve Module (DERM). The resistor module allows the DERM to monitor the deployment loop for faults and to detect when a deployment has occurred.

The resistors in the resistor module are balanced with the resistors on the arming and discriminating sensors to allow the DERM to monitor the voltage drops across the components of the deployment loop. Faults are detected during normal non-deployment conditions by monitoring these voltages. On some vehicles, the resistor module is mounted on the DERM.

SERVICE PRECAUTIONS

Note. These precautions should be observed when working with air bag systems

1. Disable air bag system before servicing any air bag system or steering column component. Failure to do this could result in accidental air bag deployment and possible personal injury. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system) .
2. After an accident, all SIR components, including harness and brackets, must be inspected. If any components are damaged or bent, they must be replaced, even if a deployment did not occur. Check steering column, knee bolster, instrument panel steering column reinforcement plate and lower brace for damage. DO NOT service resistor module, inflator module, coil assembly, discriminating sensors, arming sensor or Diagnostic Energy Reserve Module (DERM). If these components are damaged or defective, replacement is necessary.
3. After repairs, turn ignition on from passenger side of vehicle in case of accidental air bag deployment. Ensure INFLATABLE RESTRAINT light is working properly and no system faults are indicated. See «TESTING - SYSTEM OPERATION CHECK»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__testing-system-operation-check) .
4. Always wear safety glasses when servicing or handling an air bag.
5. Air bag module must be stored in its original special container until used for service. It must be stored in a clean, dry place, away from sources of extreme heat, sparks or high electrical energy.
6. When placing a live air bag module on a bench or other surface, always face air bag and trim cover up, away from surface. This will reduce motion of module if accidentally deployed.
7. After deployment, air bag surface may contain deposits of sodium hydroxide, which can irritate skin. Always wear safety glasses, rubber gloves and long-sleeved shirt during clean- up, and wash hands using mild soap and water. Follow correct disposal procedures. See «DISPOSAL PROCEDURES»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system) .
8. At no time should any electrical source be allowed near inflator on back of air bag module.
9. When carrying a live air bag module, trim cover should be pointed away from your body to minimize injury in case of accidental deployment.
10. DO NOT probe a wire through insulator; this will damage it and eventually cause failure due to corrosion.
11. Coil assembly must be replaced whenever air bag deploys.
12. When performing electrical tests, prevent accidental shorting of terminals. Such mistakes can damage fuses or components and may cause a second fault code to set, making diagnosis of original problem more difficult.
13. When using diagnostic charts to diagnose air bag system, under no circumstances should a volt/ohmmeter, test light or any type of electrical equipment not specified by manufacturer be used. See SPECIAL TOOLS.
14. If air bag system is not fully functional for any reason, vehicle should not be driven until system is repaired. Do not remove bulbs, modules, sensors or other components or in any way disable system from operating normally. If air bag system is not functional, park vehicle until repairs can be made.

SPECIAL TOOLS

To avoid deployment when working on SIR system, DO NOT use electrical test equipment such as test lights, battery or A/C-powered volt/ohmmeter or any type of electrical equipment not specified by manufacturer. See SIR RECOMMENDED TOOL table.

SIR RECOMMENDED TOOL

DISABLING & ACTIVATING AIR BAG SYSTEM

1. To disable air bag system, turn ignition switch to OFF position. Remove SIR fuse from fuse block. Disconnect Yellow SIR connector at base of steering column. Wait 15 minutes before working on vehicle. All connectors used on SIR system use Connector Position Assurance (CPA) clips to ensure connector retention.
2. To activate air bag system, turn ignition switch to OFF position. Connect Yellow 2-pin connector and CPA clip at base of steering column. Install SIR fuse. Turn ignition switch to RUN position. Observe INFLATABLE RESTRAINT indicator light. See «TESTING - SYSTEM OPERATION CHECK»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__testing-system-operation-check) .

POST-COLLISION INSPECTION

When a vehicle has been involved in a collision, certain components of the passive restraint system must be inspected or replaced. See PASSIVE RESTRAINT SYSTEM INSPECTION article in the GENERAL INFORMATION section for post-collision inspection information.

Scheme 36

1. If coil assembly has been removed from steering column and is being reinstalled, go to step 2). New coil assemblies are provided pre-centered and include a Blue plastic tab, which is snapped off once coil is installed. (Scheme 36)
2. Ensure front wheels face straight ahead when installing or removing a coil assembly. If coil is removed without wheels in straight-ahead position and steering wheel has not been moved, same coil can be reinstalled if coil hub also has not been rotated.
3. Hold coil assembly with clear bottom upward to see coil ribbon. Note there are 2 different styles of coil assemblies; one rotates clockwise and other rotates counterclockwise.
4. While holding coil assembly housing, depress spring lock and rotate hub in direction of arrow until it stops. Coil assembly should now be wound up snug against center hub. Rotate coil assembly hub in opposite direction approximately 2 1/2 turns. Release spring lock between locking tabs in front of arrow.

DEPLOYED AIR BAG

Deployed air bag modules can be disposed of as would any other part. Handle air bag module with gloves, and wear safety glasses.

UNDEPLOYED AIR BAG

Undeployed air bag modules must NOT be disposed of at normal refuse locations. Undeployed air bag modules contain substances which can cause illness or injury if handled improperly. Disposal of air bag module in any manner inconsistent with proper procedures may be a violation of federal, state and/or local laws. If possible, deploy air bag module in vehicle. See SCRAPPED VEHICLE.

Transportation of undeployed air bag modules is regulated by hazardous materials regulations of Department of Transportation (DOT) and most state governments. Special shipping procedures are required. Repair shops should check with hazardous material section of their respective state governments for applicable shipping requirements.

SCRAPPED VEHICLE

Some vehicles which have to be scrapped may have an undeployed SIR module. Follow these procedures when scrapping a vehicle with an undeployed module

1. Turn ignition switch to OFF position. Remove SIR fuse. Disconnect Yellow 2-pin connector at base of steering column. Cut harness side of SIR wiring approximately 3-6" from Yellow 2-pin connector.
2. Splice 2 wires at least 20 feet long to wiring cut from SIR harness. Connect Yellow 2-pin connector.
3. Ensure inflator module is secured to steering wheel. Remove all loose objects from front seat, and ensure no one is in vehicle. Stretch wires as far away from car as possible.
4. Connect wires to a 12-volt battery. Air bag should deploy. DO NOT touch inflator module area for 20 minutes due to heat generated during deployment. Wear gloves and safety glasses before handling deployed air bag. Wash hands with soap and water afterward.

Removal

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__service-precautions). Disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system).
2. DERM is located under right side of instrument panel. Remove console and accessory trim plates. Remove radio control head and 2 upper left trim panel screws. Flip panel down to access DERM.
3. Remove knee bolster. (Scheme 37) Remove 4 DERM left bracket bolts, and remove bracket. Remove right trim panel, driver's inner knee bolster left bracket fasteners, driver's inner knee bolster bracket and DERM inner bracket. Remove DERM harness Connector Position Assurance (CPA) clip, and disconnect connector. Remove DERM.

Scheme 37

Installation

1. Install DERM into vehicle. Install DERM harness connector and CPA clip. Install DERM inner bracket. Install and tighten driver's inner knee bolster left bracket to 116 INCH lbs. (13 N.m). Install right trim panel.
2. Install DERM left bracket, and tighten retaining bolts to 116 INCH lbs. (13 N.m). To complete installation, reverse removal procedure. Check INFLATABLE RESTRAINT indicator light to ensure system is functioning properly. See «TESTING - SYSTEM OPERATION CHECK»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__testing-system-operation-check) .

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__service-precautions). Disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system).
2. Arming sensor is located under right side of instrument panel. Remove control head assembly. Remove arming sensor connector from passenger knee bolster inner bracket. Remove Connector Position Assurance (CPA) clip, and disconnect electrical connector. Remove arming sensor retaining bolts and arming sensor. (Scheme 37)

Install arming sensor into vehicle with arrow pointing toward front of vehicle. Install arming sensor retaining bolts, and tighten to 19 ft. lbs. (25 N.m). To complete installation, reverse removal procedure. Check INFLATABLE RESTRAINT indicator light to ensure system is functioning properly. See TESTING - SYSTEM OPERATION CHECK .

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__service-precautions). Disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system).
2. Left forward discriminating sensor is located on left frame rail. To remove left front discriminating sensor, remove battery, ECM and support. Remove sensor mounting bolts and Connector Position Assurance (CPA) clip. Disconnect sensor electrical connector from retainer. Disconnect electrical connector, and remove sensor from vehicle.
3. Right forward discriminating sensor is located on right frame rail. To remove right front discriminating sensor, remove 6 right front rocker panel retaining screws. Remove right front fender retaining bolts, and remove fender. Peel back rear portion of wheelhouse-to-hood seal. Remove right lower wheelhouse retaining bolts, and remove lower wheelhouse.
4. Remove 2 windshield washer reservoir retaining bolts. Loosen remaining washer reservoir bolt, and rotate reservoir to access sensor. Remove sensor mounting bolts, and disconnect electrical connector from retainer. Remove CPA clip, and disconnect electrical connector. Remove sensor from vehicle. (Scheme 37)

Install left and right front discriminating sensors with arrow on sensor pointing toward front of vehicle. Install sensor attaching bolts, and tighten to 19 ft. lbs. (25 N.m). To complete installation, reverse removal procedure. Check INFLATABLE RESTRAINT indicator light to ensure system is functioning properly. See TESTING - SYSTEM OPERATION CHECK .

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__service-precautions) . Disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system) .
2. SIR coil assembly is located under steering wheel, in steering column. Remove inflator module. See «INFLATOR MODULE»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system) . Remove horn contact wire. Remove SIR coil assembly retaining ring. Remove SIR coil from shaft, and allow to hang freely. Remove wave washer from steering shaft.
3. Using Shaft Lock Remover (J-23653), depress shaft lock plate and remove shaft lock retaining ring. Remove shaft lock plate, turn signal canceling cam, upper bearing spring, upper bearing inner race seat and inner race.
4. Position turn signal to right turn position. Remove multifunction lever. Remove column housing cover end cap by pulling rearward (toward front of vehicle). Disconnect electrical harness connector, and remove grommet. Pull toward driver's door to release detent/multifunction lever. Remove screw and signal switch arm. Remove turn signal switch screws, hazard knob assembly and turn signal switch. Allow switch to hang freely.
5. Remove Yellow connector shroud from Black terminal connector. Remove wiring protector, and carefully pull wire through housing shroud, column and lock housing cover.

1. Install coil assembly wire through lock housing cover, column housing and housing shroud. Allow coil to hang freely. Ensure slack is never present in coil assembly wire in steering column, otherwise coil assembly wire damage may occur.
2. Install connector shroud to terminal connector. Install turn signal switch, and tighten screws to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system) . Install wiring protector, hazard knob assembly, multifunction lever, upper bearing spring, turn signal canceling cam assembly and shaft lock. NOTE: If shaft lock retaining ring is damaged or deformed, replacement is necessary.
3. Align shaft lock retaining ring to block tooth on shaft. Depress shaft lock and install shaft lock retaining ring. Ensure SIR coil hub is centered.
4. Set steering shaft so block teeth on upper steering shaft are at 12 o'clock and 6 o'clock positions. With wheels on vehicle in straight-ahead position, set ignition switch to LOCK position to avoid coil assembly damage. Coil assembly will become un-centered if column is separated from steering gear and allowed to rotate or if centering spring is depressed, allowing hub to rotate while coil is removed from column.
5. Install wave washer. Using horn tower on canceling cam inner ring and projections on outer ring for alignment, install coil. Install coil retaining ring. Gently pull lower coil assembly wire to remove any wire kinks inside column. To complete installation, reverse removal procedure. Check INFLATABLE RESTRAINT indicator light to ensure system is functioning properly. See «TESTING - SYSTEM OPERATION CHECK»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__testing-system-operation-check) .

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__service-precautions) . Disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system) .
2. Inflator module is located on steering wheel hub. Remove screws and nuts from underside of steering wheel. Partially remove inflator module, and disconnect steering wheel inflator module connector, Connector Position Assurance (CPA) clip and horn contact from inflator. Remove inflator module.

1. Install horn contact, steering wheel inflator module connector and CPA clip. Install inflator module to steering wheel.
2. Secure with screws torqued to 87 INCH lbs. (9.7 N.m). To complete installation, reverse removal procedure. Check INFLATABLE RESTRAINT indicator light to ensure system is functioning properly. See «TESTING - SYSTEM OPERATION CHECK»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__testing-system-operation-check) .

Removal & Installation

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__service-precautions) . Disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system) .
2. Resistor module is located under center of instrument panel. Remove radio control head assembly. Unclip resistor module from instrument panel carrier. Remove Connector Position Assurance (CPA) clip, and disconnect electrical connector. Remove resistor module from vehicle. To install, reverse removal procedure. Check INFLATABLE RESTRAINT indicator light to ensure system is functioning properly. See «TESTING - SYSTEM OPERATION CHECK»(/chevrolet/corvette/c4-1984-1998/remont/airbag/#air-bag-restraint-system__testing-system-operation-check) .

TESTING - SYSTEM OPERATION CHECK

If system is functioning normally, INFLATABLE RESTRAINT indicator light will flash 7-9 times when ignition switch is turned to ON position, and then go off.

Note. Four possible indicator light conditions warn of system failure

1. Light does not illuminate at all.
2. Light comes on while vehicle is driven.
3. Light flashes 7-9 times and remains on.
4. Light does not flash but remains lit when ignition is turned on.

SIR system faults are usually due to a disconnected/loose electrical connector caused by previous service on vehicle. Always check Yellow connector at base of steering column.

WIRE REPAIR

Because of sensitive nature of circuitry, manufacturer has developed special wiring repair procedures. Wire Repair Kit (J-38125-A) contains special sealed splices for use in repairing SIR wiring. Sealed splices are a heat shrink sleeve with sealing adhesive to produce a sealed splice. Kit also contains a cross-hatched core crimp to ensure positive contact for low energy circuits.

If any terminal or connector in SIR wire harness (except pigtails) is damaged, component can be repaired using a connector repair assembly pack. Terminals in SIR system are manufactured of a special metal to provide necessary contact for low energy circuits. These terminals are only available in wiring kit and no other terminal should be substituted.

If an SIR wire pigtail is damaged, entire component (including pigtail) should be replaced. Under no circumstances should wire, connector or terminal repair be attempted on arming sensor, passenger compartment discriminating sensor, forward discriminating sensor, inflator module or SIR coil assembly.

If any wire except a pigtail is damaged, wire can be repaired by splicing in a new section of wire of same gauge. Sealed splices and crimping tool must be used for these splices. To open wiring harness, remove tape as necessary. To avoid wire insulation damage, manufacturer recommends using a sewing seam ripper. Refer to instructions in kit for wire repair procedure.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

Scheme 38

See also:
• PASSIVE RESTRAINT SYSTEM INSPECTION
• SERVICE PRECAUTIONS
• TESTING - SYSTEM OPERATION CHECK
• SIR DIAGNOSTIC SYSTEM CHECK
• DISABLING & ACTIVATING AIR BAG SYSTEM