BRAKE WARNING LIGHT ILLUMINATE RWAL CODE 7-REPAIR PROCEDURE

SUBJECT: BRAKE WARNING LIGHT ILLUMINATES AND RWAL CODE 7 (PROCEDURE TO INSTALL A/C REL

VEHICLES AFFECTED: 1988-90 C/K, 1989-91 S/T WITHOUT A/C

Some 1989-91 S/T and 1988-90 C/K trucks without air conditioning may experience a condition in which the brake warning light is illuminated and a false code 7 is set to the RWAL ECU memory. This condition is most often observed on trucks equipped with manual transmission.

It had been determined that a false code 7 can be set on these vehicles if the following conditions are met:

1. The blower motor is set on high and

2. The ignition is turned off and the brakes are applied while the truck is still moving.

Because of the unusual circumstances owners may drive for some time between occurrences of code 7.

This condition is caused by slow blower motor "wind down". When the ignition is cycled off the blower motor will wind down and may supply the RWAL ECU with sufficient enough power to set a false code 7. To correct this concern in Production, a change was made to ECU modules in August, 1990.

Technicians can identify the new ECUs from the old by examining the long bar code sticker on the unit. Old ECUs have 15 digit alphanumeric codes at the bottom of the sticker beginning with 912349K. The new ECUs also have a 15 digit alphanumeric code but the code begins with 919220K.

To repair this condition a relay should be installed between the blower motor and the resistor block to prevent any feed back of current to the RWAL system from the high blower line.

Service Procedure - S/T Trucks: ------------------------------- 1. Disconnect the negative battery cable.

2. Using a 1/8" drill bit and service high blower relay #14036273 as a guide, drill two 1/4" deep holes into the blower motor case between the blower motor and the resistor block (see Figures 2A and 2B for location). Tape should be used to mark off 1/4" on the drill bit to avoid drilling to deeply and damaging and internal blower motor components.

3. Cut a piece of red 14 gauge wire approximately 20" long. Strip each end of the wire and crimp a female "quick connect straight" terminal on one end and a "ring tongue" terminal on the other end.

4. Cut one piece of black 14 gauge wire approximately 5" long and attach connectors to the wire in the same fashion as given in Step 3.

5. Disconnect the orange electrical lead from the resistor block. Cut the orange lead to the blower motor where it enters the female "quick connect straight" terminal that was just removed from the resistor block. Strip the end and attach a new female quick "connect straight" terminal to it and connect to terminal B of the new high blower relay connector.

6. Cut one piece of brown 14 gauge electrical wire to approximately 4" long. Strip both ends of the wire and crimp a female "quick connect straight" terminal to each end.

7. Make the following connections as shown in Figure 1.

- Red wire to terminal E of high blower motor relay connector and to the junction block connection located on the cowl

- Black wire to blower motor case mounting bolt for chassis ground. Choose the nearest bolt and scrape lightly around the bolt hole to assure a good ground.

- Remaining end of black wire to terminal A of high blower motor relay connector

- Brown wire to terminal D high blower relay connector and terminal 52 of resistor block.

- Remaining orange wire (ignition lead) to terminal C of high blower relay connector.

8. Firmly install the high blower connector to the high blower motor relay.

9. Bolt the high blower motor relay to the blower motor case using two 5/8" long (size 14) hex head sheet metal screws through the pre-drilled holes.

10. Attach negative battery cable.

11. Verify that the blower motor operates properly. If the blower motor does not function properly check all connections, and ground for poor fit or interference.

12. Using Tech 1, clear any codes in the RWAL memory and test drive the vehicle under the conditions outlined above to assure the false code 7 does not set.

Service Procedure - C/K Trucks: ------------------------------- 1. Disconnect the negative battery cable.

2. Remove instrument panel glove box compartment.

3. Using a 1/8" drill bit and service high blower relay #14036273 as a guide, drill two 1/4" deep holes into the blower motor case between the blower motor and the resistor block. Refer to Figures 2A and 2B for approximate relay location (S/T shown, C/K typical). Tape should be used to mark off 1/4" on the drill bit to avoid drilling to deeply and damaging any internal blower motor components.

4. Cut a piece of red 14 gauge wire approximately 20" long. Strip each end of the wire and crimp a female "quick connect straight" terminal on one end and a "ring tongue" terminal on the other end.

5. Cut one piece of black 14 gauge wire approximately 5" long and attach connectors to the wire in the same fashion as given in Step 4.

6. Disconnect the orange electrical lead from the resistor block. Cut the orange lead to the blower motor where it enters the female "quick connect straight" terminal that was just removed from the resistor block. Strip the end and attach a new female quick "connect straight" terminal to it and connect to terminal B the new high blower relay connector.

7. Cut one piece of black 14 gauge electrical wire to approximately 4" long. Strip both ends of the wire and crimp a female "quick connect straight" terminal to each end.

8. Make the following connections, refer to Figure 1.

- Red wire to terminal E of high blower motor relay connector and to the junction block connection located on the cowl.

- Black wire to blower motor case mounting bolt for chassis ground. Choose the neatest bolt and scrape lightly around the bolt hole to assure a good ground.

- Remaining end of black wire to terminal A of high blower motor relay connector.

- Brown wire to terminal D high blower relay connector and terminal 52 of resistor block.

- Remaining orange wire (ignition lead) to terminal C of high blower relay connector.

9. Firmly install the high blower connector to the high blower motor relay.

10. Bolt the high blower motor relay to the blower motor case using two 5/8" long (size 14) hex head sheet metal screws through the pre-drilled holes.

11. Attach negative battery cable.

12. Verify that the blower motor operates properly. If the blower motor does not function properly check all connections, and ground for poor fit or interference.

13. Using Tech 1, clear any codes in the RWAL memory and test drive the vehicle under the conditions outlined above to assure the false code 7 does not set.

SERVICE PARTS INFORMATION

Part Number Description ----------- ---------------- 14036273 High Blower Relay

2984911 High Blower Relay Connector

14 gauge electrical wire and connectors are available locally at most electronic stores.

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.