GM Full-Size Trucks 1988-1998 Repair Information

Trouble codes

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The following is a list of the OBD-I trouble codes for the four wheel anti-lock brake system.



Code 21: right front speed sensor or circuit open
 
Code 22: missing right front speed signal
 
Code 23: erratic right front speed signal
 
Code 25: left front speed sensor or circuit open
 
Code 26: missing left front speed signal
 
Code 27: erratic left front speed signal
 
Code 29: simultaneous drop-out of front speed sensors
 
Code 35: vehicle speed sensor or open circuit
 
Code 36: missing vehicle speed sensor signal
 
Code 37: erratic vehicle speed sensor signal
 
Code 38: wheel speed error
 
Codes 41 through 54: control valves
 
Codes 61 through 63: reset switches
 
Code 65 and 66: open or shorted pump motor relay
 
Code 67: open motor circuit or shorted BPMV output
 
Code 68: locked motor or shorted motor circuit
 
Codes 71 through 74: memory errors
 
Code 81: brake switch circuit shorted or open
 
Code 86: shorted anti-lock indicator lamp
 
Code 87: shorted brake warning lamp
 

The following is a list of the OBD-II trouble codes for the four wheel anti-lock brake system.



Code C0021: right front wheel speed sensor circuit open or shorted to battery
 
Code C0022: right front wheel speed sensor signal missing
 
Code C0023: right front wheel speed sensor signal erratic
 
Code C0025: left front wheel speed sensor circuit open or shorted to battery
 
Code C0026: left front wheel speed sensor signal missing
 
Code C0027: left front wheel speed sensor signal erratic
 
Code C0029: simultaneous drop-out of front wheel speed signals
 
Code C0035: rear speed sensor circuit open or shorted to battery
 
Code C0036: rear speed signal missing
 
Code C0037: rear speed signal erratic
 
Code C0038: wheel speed signal malfunction
 
Code C0041: right front isolation solenoid circuit open
 
Code C0042: right front dump solenoid circuit open
 
Code C0043: right front isolation solenoid circuit shorted
 
Code C0044: right front dump solenoid circuit shorted
 
Code C0045: left front isolation solenoid circuit open
 
Code C0046: left front dump solenoid circuit open
 
Code C0047: left front isolation solenoid circuit shorted
 
Code C0048: left front dump solenoid circuit shorted
 
Code C0051: rear isolation solenoid circuit open
 
Code C0052: rear dump solenoid circuit open
 
Code C0053: rear isolation solenoid circuit shorted
 
Code C0054: rear dump solenoid circuit shorted
 
Code C0065: pump motor relay circuit open
 
Code C0066: pump motor relay circuit shorted
 
Code C0067: pump motor circuit open
 
Code C0068: pump motor locked or pump motor circuit shorted
 
Codes C0071 through C0074: EBCM internal fault
 
Code C0081: stoplamp switch circuit always closed or shorted
 
Code C0086: anti-lock indicator lamp circuit shorted to battery
 
Code C0087: brake warning lamp circuit shorted to battery
 

 
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