GM Astro/Safari 1985-1996 Repair Guide

Self Diagnostics

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READING TROUBLE CODES



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Pinout of the ALDL connector

Rear Wheel Anti-lock Brakes

The trouble codes are read by jumping terminal A and terminal H of the ALDL (assembly line diagnostic link) with a jumper wire. Observe the flashing of the brake warning light. The terminals must be jumped for about 20 seconds before the code will begin to flash.

Count the number of short flashes starting from the long flash. Include the long flash as a count. Sometimes the first count sequence will be short, however, following counts will be accurate.

If there is more than one failure, only the first recognized code will be retained and flashed.



Code 1-ECU malfunction
 
Code 2-Open isolation valve or faulty ECU
 
Code 3-Open dump valve or faulty ECU
 
Code 4-Grounded anti-lock valve switch
 
Code 5-Excessive dump valve activity during stop
 
Code 6-Erratic speed system
 
Code 7-Shorted isolation valve or faulty ECU
 
Code 8-Shorted dump valve or faulty ECU
 
Code 9-Open speed signal circuit
 
Code 10-Brake lamp switch circuit
 
Code 11-Faulty ECU
 
Code 12-Faulty ECU
 
Code 13-Faulty ECU
 
Code 14-Faulty ECU
 
Code 15-Faulty ECU
 

4-Wheel Anti-lock Brakes
EXCEPT 1996 MODELS

The trouble codes are read by jumping terminal A and terminal H of the ALDL (assembly line diagnostic link) with a jumper wire. Observe the flashing of the ANTI-LOCK warning light. The terminals must be jumped for about 20 seconds before the code will begin to flash.

Count the number of short flashes starting from the long flash. Include the long flash as a count. Sometimes the first count sequence will be short, however, following counts will be accurate.

If there is more than one failure, only the first recognized code will be retained and flashed.



Code 21-RF speed sensor or circuit open
 
Code 22-Missing RF speed signal
 
Code 23-Erratic RF speed sensor
 
Code 25-LF speed sensor or circuit open
 
Code 26-Missing LF speed signal
 
Code 27-Erratic LF speed sensor
 
Code 29-Simultaneous drop out of front speed sensors
 
Code 31-RR speed sensor or circuit open
 
Code 32-Missing RR speed signal
 
Code 33-Erratic RR speed signal
 
Code 35-VSS or LR speed sensor or circuit open
 
Code 36-Missing VSS or LR speed sensor or circuit open
 
Code 37-Erratic VSS or LR speed sensor signal
 
Code 38-Wheel speed error
 
Code 41-54-Control valves
 
Code 61-63-Reset switches
 
Code 65-66-Open or shorted pump motor relay
 
Code 67-Open motor circuit or shorted BPMV output
 
Code 68-Locked motor or shorted motor circuit
 
Code 71-74-Memory errors
 
Code 81-Brake switch circuit shorted or open
 
Code 86-Shorted anti-lock indicator lamp
 
Code 88-Shorted brake warning lamp
 

1996 MODELS

Trouble codes on the 1996 vehicles can only be read using a scan tool. It is not possible to read the trouble codes by the flashing light method. The trouble codes are the same as the earlier year vehicles.

CLEARING TROUBLE CODES



On 1985-95 vehicles the trouble codes may be cleared using a Tech I scan tool or by performing the following procedures. On 1996 vehicles, the trouble codes can only be cleared by the Tech 1 scan tool.

  1. Turn the ignition switch to the RUN position.
  2.  
  3. Use a jumper wire to ground the ALDL terminal A to H for 2 seconds.
  4.  
  5. Remove the jumper wire for 2 seconds.
  6.  
  7. Repeat the grounding and ungrounding 2 more times.
  8.  
  9. Check that the memory is cleared by making a diagnostic request.
  10.  
  11. Turn the ignition switch OFF .
  12.  

 
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