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BRAKE CODES.docx

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Pulling Chevy Truck OBDI Brake Codes Information Here's information on pulling Chevy Truck OBDI Brakes codes for the RWAL and AWAL brake systems and codes. PROCEDURE: Diagnostic Trouble Codes (DTC) 's can be displayed by jumping terminals A and H of the Data Link Connector and observing the flashing of the BRAKE warning light. This should only be done when the brake lamp is ON . The terminals must be jumped for about 20 seconds before the code will begin to flash. Count the
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  Pulling Chevy Truck OBDI Brake Codes Information Here's information on pulling Chevy Truck OBDI Brakes codes for the RWAL and AWAL   brake systems and codes.   PROCEDURE:  Diagnostic Trouble Codes (DTC) 's can be displayed by jumping terminals A and H   of the Data Link Connector and observing the flashing of the BRAKE warning light.   This should only be done when the brake lamp is ON .   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, subsequent   flashes will be accurate. If there is more than one failure, only the first recognized code   will be retained and flashed. NOTES:  DTC's 6, 9 and 10 will only turn the BRAKE lamp on while the fault exists. These are   soft codes faults and can only be read with the Tech 1 scan tool.   Do not jump terminals A to H if the BRAKE lamp is not on. Jumping the terminals   with the BRAKE lamp off will set a false DTC 9. This will turn the BRAKE lamp on   and disable the antilock system.         1, 11, & 12 ECU Malfunction      2 Open Isolation Valve or   Malfunctioning ECU      3 Open Dump Valve or ECU   Malfunction    4 Grounded Antilock Valve Reset Switch    5 Eccessive Actuations of the Dump Valve      6 Erratic Speed Signal      7 Shorted Isolation Valve or Faulty ECU      8 Shorted Dump Valve or   Faulty ECU      9 Open Circuit to Speed Signal      10 Brake Lamp Switch Circuit      13, 14 and 15 ECU Malfunction   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   That 92 is the second year they had the 4wh ABS on Blazers. You can pull the code yourself by jumping A to H on the DLC/ALDL and counting the flashes of the anti-lock light. Codes are different for 4wh ABS and the more common (then) 2w RWAL ABS. When jumping A-H you may hear the ABS motor run. Regarding the measured voltage: varied between .5 volts and 4.5volts AC depending upon speed of the drive shaft I think that's a problem. At hand spinning speed they should be around 0.350v and might drop to 0.200v if dirty. Maybe you should test them differently. Unplug each front sensor to measure while spinning at hand speed. This isolates problem and each acts as reference for other side. Seems that super low 0.5v has to be a problem. The back I think just shares a common sensor from the rear that goes through the speed buffer first before reaching antilock. That H contact at DLC is connected to the wire from buffer to ABS and if you were to measure voltage there you should see about 1-5v. A much high read suggests bad ground for ABS.  Problem may be coming from the buffer. See if you have problem with any of these: cruise control, shift points, speedo reading right.  

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Jul 23, 2017

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Jul 23, 2017
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