oldspeedr

I have the typical 1990 INFL REST lamp on my 1990 coupe. I have read many posts concerning this and understand the diag procedures. I have also read about installing a 2 ohm resistor in the "line at the base of the steering column" that defeats the airbag system. Is this as simple as finding the yellow lead at the base of the column and inserting a 2 ohm resistor?

billschroeder5842

No, it is not that simple. You will most likley need to clean and reground your modules located on the frame behind the battery and under the radiator fill. This seems to be a common and there are many write ups on how to do this.

HOWEVER... you should get an OBD1 reader and do a diagnostic on the system. The system is seriously complex and it could be anything. Plus, you will need to have the scanner to clear codes, or your light will just come back on.

oldspeedr

Nothing computer related is ever simple, is it? I located the sensors this morning and have read the diag grounding pin k to retrieve codes. Even that wont be simple as the connector is facing the firewall.

jts90vette

If I'm not mistaken, an OBD1 scanner will not work on SIR codes on a 1990, codes can only be cleared by grounding and ungrounding pin "k" of the ALDL. It is a complex procedure but can be done.

GM did issue a TSB on this SIR condition, TSB#90-436-9j (11/07/1991). 99% of all SIR lights om 1990 models are a result of corrosion between the impact sensors and the frame rails resulting in a bad ground.

ChumpVette

Junk OBD1 scanners will not handle the SIR codes, nor most other codes other than ECM codes.

A proper scanner will read the codes and then clear them.

Joe C

if anyone is interested, here's a copy of the subject TSB -

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1990: Service Bulletin: SIR Diagnostics and Procedures to Prevent Codes 16 and 26 Due to Corrosion

Subject: SERVICE MAN. UPDATE SEC.9J A/B REV. SIR DIAGNOSTIC PROCEDURE
Model and Year: 1990 CORVETTE
Source: Chevrolet Service Bulletin
Bulletin Number: 90-436-9J - (11/07/1991)

Some 1990 Corvettes have set SIR Sensor Codes 16 and 26. The DERM has detected an unacceptably high resistance between the SIR sensor and the frame rail, most likely due to a buildup of corrosion on the mounting surfaces. New service procedures have been developed to remove the corrosion and help prevent it from building up again. Removal and installation procedures, revised to address the corrosion issue, are attached. Please use these new procedures for all 1990 Corvette SIR Code 16 and Code 26 situations.

IMPORTANT! - The corrosion condition and repair procedures apply only to 1990 Corvette; 1991 and subsequent vehicles do not set sensor codes due to this condition.

The new procedures require the use of a special grease (P/N 12345579) and two external-tooth lock washers (P/N 11501869 - 8 mm, P/N 121753 - 6 mm) for the sensor mounting bolts.

Along with the new procedures, please remember the following:

1. The "SIR Diagnostic System Check" in Section 9J-A must be the starting point of any SIR diagnostics. The "SIR Diagnostic System Check" will verify proper "INFL REST" warning lamp operation and will lead you to the correct chart to diagnose any SIR faults. Bypassing these procedures may result in extended diagnostic time, incorrect diagnosis, and incorrect parts replacement.

2. If both Code 15 and 16 (or 25 and 26) are set, use the Code 16(26) diagnosis chart first. Then, if Code 15(25) resets after the Code 16(26) is corrected, perform the Code 15(25) diagnosis.

3. To clear 1990 Corvette SIR codes, use the Tech 1 (part number T1 or 94-00101-A) with the 1991 Body Systems Cartridge (TKO4040A) and 1990 Dual UART/SIR Adapter (TA00065). The 1991 Body Systems Cartridge must be used because the 1990 Body Systems Cartridge has no SIR code-clearing capabilities for the 1990 Corvette.

If the Tech 1, cartridge, and adapter are not available, codes can be cleared by grounding Terminal "K" of the ALDL connector as called out below under "ALDL Code-Clearing Technique". If using the ALDL procedure, be sure to follow it completely and exactly; codes can be difficult to clear using this method if the procedure is not carefully followed.

4. If the ignition is turned "ON" while any part of the 199O Corvette SIR system is disconnected, a code will set and remain set, even if the component is reconnected, until cleared by the technician.

ALDL CODE-CLEARING TECHNIQUE

When using this code-clearing technique, a digital wristwatch can be quite helpful. The timing sequence discussed below is very important to successfully clearing codes. The watch can help you with timing the 3-second intervals more exactly.

1.Turn ignition "OFF".

2. Ground ALDL terminal "K".

3. Turn ignition "ON". Do not start the car however.

4. Wait for codes to begin flashing (approximately 5 seconds). When codes begin flashing, unground ALDL terminal "K" for 3 seconds +/- 1/2 second.

5. After ungrounding terminal "K" as described in Step 4, ground it again for 3 seconds +/- 1/2 second.

6. Unground ALDL terminal "K", and wait 10 seconds. Before turning ignition "OFF", ground terminal "K" again and verify that Code 12 flashes six (6) times.

If Code 12 does not flash six (6) times, codes have not been cleared properly. Begin clearing procedure again starting with Step 1.

CODE 16 FRONT SENSOR #1 (LH) (SENSOR FAULT) Circuit Description: In a frontal crash of sufficient force, the Front Discriminating Sensor Switch closes, providing a path to ground for the deployment loop current. The sensor contains additional circuitry, used by the DERM for diagnostics. If the DERM measures more than a certain resistance value between the redundant ground circuit and the DERM's own ground, Code 16 will set. This code will also set if the DERM measures less than a certain resistance between the sensor feed circuit and B + or the diagnostic return circuit and B +.

Severe corrosion under the sensor mounting bracket may cause a Code 16. Refer to "Left Sensor" on attached pages to remove sensor, inspect for corrosion, and correct corrosion if found. "Left Sensor" also instructs on use of special grease and washers to help prevent recurrence of Code 16 due to corrosion.

The Fasten Seat Belt indicator will stay "ON" continuously when an SIR code has been set.

If power is applied to the SIR system while any component is not properly connected, an additional code will be set for the disconnected SIR component.

CODE 26 FRONT SENSOR #2 (RH) (SENSOR FAULT) Circuit Description: In a frontal crash of sufficient force, the Front Discriminating Sensor switch closes, providing a path to ground for the deployment loop current. The sensor contains additional circuitry, used by the DERM for diagnostics. If the DERM measures more than a certain resistance value between the redundant ground circuit and the DERM's own ground, Code 26 will set. This code will also set if the DERM measures less than a certain resistance between the sensor feed circuit and B + or the diagnostic return circuit and B +.

If a Code 26 has set, a Code 25 may also be set.

Severe corrosion under the sensor mounting bracket may cause a Code 26. Refer to "Right Sensor" to remove sensor, inspect for corrosion, and correct corrosion if found. "Right Sensor" also instructs on use of special grease and washers to help prevent recurrence of Code 26 due to corrosion.

The Fasten Seat Belt indicator will stay "ON" continuously when an SIR code has been set.

If power is applied to the SIR system while any component is not properly connected, an additional code will be set for the disconnected SIR component.

FORWARD DISCRIMINATING SENSORS Caution should be used to assure proper location of sensors to the front frame rails. The keying of the sensors to the frame rails through the differently sized mounting bolt holes in the sensor mounting plate should never be modified in the field.

CAUTION: Be very careful when handling a sensor. Never strike or jar a sensor. If you do, it could cause deployment and result in personal injury or improper operation of the Supplemental Inflatable Restraint (SIR) system. All sensor mounting bolts must be carefully torqued to assure proper sensor operation. Never power up the SIR system when any sensor is not rigidly attached to the vehicle, since the sensor is easily activated when not attached and could result in a deployment.

LEFT SENSOR

CAUTION: The following procedures must be followed in the order listed to temporarily disable the Supplemental Inflatable Restraint (SIR) system and prevent false diagnostic codes from setting. Failure to follow this procedure could result in possible air bag deployment, personal injury, or unneeded SIR system repairs.

Remove or Disconnect

1. Turn ignition switch "OFF."

2. Left sound insulator; refer to INSTRUMENT PANEL, GAGES, & CONSOLE (SECTION 8C).

3. Connector Position Assurance (CPA) and yellow two-way SIR connector at base of steering column.

4. Battery; refer to BATTERY (SECTION 6D1).

5. ECM and support; refer to DRIVEABILITY AND EMISSIONS 9SECTION 6E3).

6. Sensor mounting bolts.

7. Sensor electrical connection from retainer; disconnect connection.

8. Sensor from vehicle.

IMPORTANT

Clean Sensor mounting bracket surface, frame rail mounting surface, and mounting bolts and holes to remove any paint or corrosion that might interfere with a good electrical ground.

CAUTION Proper operation of the sensors and Supplemental inflatable Restraint (SIR) system requires that repairs to the vehicle structure return it to its original production configuration. Deployment requires, at a minimum, replacement of the DERM, both forward discriminating sensors, the SIR Coil Assembly, and the Inflator Module. Any visible damage to the sensors, DERM, and/or the DERM mounting brackets requires replacement, and the steering wheel must be dimensionally inspected, whether deployment occurred or not.

Install or Connect

1. Apply a thin layer of special grease P/N 12345579 to the frame rail mounting surface and the mounting flange of the sensor. Do not apply the grease to the mounting bolts or holes.

2. Forward discriminating sensor, with arrow pointing toward front of vehicle.

3. External tooth lock washers, P/N 11501869 (8 mm) and 121753 (6 mm) to mounting bolts.

4. Sensor mounting bolts. Ensure that washers are between bolt head and senor mounting flange, not between mounting flange and frame rail. Tighten Front (13 mm head) bolt to 25 N.m (19 lb. ft.) - Rear (10 mm head) bolt to 14 N.m (125 lb. in.)

5. Sensor electrical connection, then clip completed connection into retainer.

6. ECM and support; refer to DRIVEABILITY AND EMISSIONS (SECTION 6E3).

7. Battery; refer to BATTERY (SECTION 6D1).

8. Yellow two-way SIR connector at base of steering column and Connector Position Assurance (CPA).

9. Left sound insulator; refer to INSTRUMENT PANEL, GAGES & CONSOLE (SECTION 8C).

10. Perform "SIR Diagnostic System Check" as outlines in SIR SYSTEM DIAGNOSIS (SECTION 9JA).

RIGHT SENSOR

CAUTION The following procedures must be followed in the order listed to temporarily disable the Supplemental Inflatable Restraint (SIR) system and prevent false diagnostic codes from setting. Failure to follow this procedure could result in possible air bag deployment, personal injury, or unneeded SIR system repairs.

Remove or Disconnect

1. Turn ignition switch "OFF."

2. Left sound insulator; refer to INSTRUMENT PANEL, GAGES & CONSOLE (SECTION 8C).

3. Connector Position Assurance (CPA) and yellow two-way SIR connector at base of steering column.

4. Six front right-side rocker panel retaining screws.

5. Right-side front fender "grill panel" retaining bolts, remove fender.

6. Peel back rear portion of wheelhouse-to-hood seal.

7. Right-side lower wheelhouse retaining bolts; remove lower wheelhouse.

8. Two front windshield washer reservoir retaining bolts.

9. Loosen remaining washer reservoir bolt; rotate reservoir to access sensor.

10. Sensor mounting bolts.

11. Sensor electrical connection from retainer; disconnect connection.

12. Sensor from vehicle.

IMPORTANT

Clean Sensor mounting bracket surface, frame rail mounting surface, and mounting bolts and holes to remove any paint or corrosion that might interfere with a good electrical ground.

CAUTION: Proper operation of the sensors and Supplemental Inflatable Restraint (SIR) system requires that repairs to the vehicle structure return it to its original production configuration. Deployment requires, at a minimum, replacement of the DERM, both forward discriminating sensors, the SIR coil Assembly, and the Inflator Module. Any visible damage to the sensors, DERM, and/or the DERM mounting brackets requires replacement, and the steering wheel must be dimensionally inspected, whether deployment occurred or not.

Proper operation of the forward discriminating sensor requires the sensor be rigidly attached to the vehicle structure and that the arrow on the sensor be pointing toward the front of the vehicle.

Install or Connect

1. Apply a thin layer of special grease P/N 12345579 to the frame rail mounting surface and the mounting flange of the sensor. Do not apply the grease to the mounting bolts or holes.

2. Forward discriminating sensor, with arrow pointing toward front of vehicle.

3. External tooth lock washers, P/N 11501869 (8 mm) and 121753 (6 mm) to mounting bolts.

4. Sensor mounting bolts. Ensure that washers are between bolt head and sensor mounting flange, not between mounting flange and frame rail. Tighten Front (13 mm head) bolt to 25 N.m (19 lb. ft.) - Rear (10 mm head) bolt to 14 N.m (125 lb. ft.)

5. Sensor electrical connection, then clip completed connection into retainer.

6. Position windshield washer reservoir; install retaining bolts.
Tighten Reservoir mounting screws to 10 N.m (89 lb. in.)

7. Lower wheelhouse and retaining bolts. Tighten Wheelhouse to "U"-nut bolts to 6 N.m (54 lb. in.). - Wheelhouse to frame member bolts to 9 N.m (80 lb. in.).

8. Reposition wheelhouse -to-hood seal.

9. Right-side front fender ("grill panel"); install retaining bolts.

10. Six front right-side rocker panel retaining screws.

11. Yellow two-way SIR connector at base of steering column and Connector Position Assurance (CPA).

12. Left sound insulator; refer to INSTRUMENT PANEL, GAGES & CONSOLE (SECTION 8C).

13. Perform "SIR Diagnostic System Check" as outlined in SIR SYSTEM DIAGNOSIS (SECTION 9JA).

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http://www.corvetteactioncenter.com/...vised-561.html

oldspeedr

Well my friends, I scanned and got a code 26. Having just purchased the car, I have no idea how or when the code was set. I performed the clear codes routine and got it on the third try. Now I just get 12 codes. We'll see how long it lasts. But for now, no infl rest light! Thanks for your help. I'll keep you posted.

jts90vette

Code 12 is a "check" code and indicates all is good. Code 26 is the passenger side impact sensor. If you didn't follow the TSB for corrosion on the frame rail, the light will return "IF" all the SIR components are working correctly.

oldspeedr

At this point, I didn't chase the 26 code. You all have provided much info and from all I've read I know that lots of things can be an issue from grounding to problem components that are out of production. I figured I'd scan and clear, see what happens and then investigate any future codes per the tsb.