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HOMESERVICE MANUALSPONTIAC1997GRAND PRIX GTP, 4D SEDANREPAIR AND DIAGNOSIS (SINGLE PAGE)BRAKESANTI-LOCK BRAKESANTI-LOCK BRAKE SYSTEM WITH TRACTION CONTROL SYSTEM - ABS-VIDIAGNOSTIC TROUBLE CODES (DTCS)DTC C1256: LEFT FRONT ABS MOTOR CIRCUIT OPEN
1997 Pontiac Grand Prix GTP, 4D Sedan

DTC C1256: Left Front Abs Motor Circuit Open

1997 Pontiac Grand Prix GTP, 4D SedanSECTION DTC C1256: Left Front Abs Motor Circuit Open
  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK . After performing diagnostic system check, go to next step.
  2. If DTC C1256 occurs intermittently, go to step 13). If DTC C1256 does not occur intermittently, go to next step.
  3. Turn ignition off. Disconnect 6-pin ABS motor pack connector. Using DVOM, measure resistance between left front motor high circuit and left front motor low circuit of motor pack connector (component side). See WIRING DIAGRAMS . If resistance is 0.2-1.5 ohms, go to next step. If resistance is not 0.2-1.5 ohms, go to step 8).
  4. Disconnect EBCM/EBTCM connector. Using DVOM, measure resistance of left front motor high circuit between motor pack connector (harness side) and EBCM/EBTCM connector. See WIRING DIAGRAMS . If resistance is 0-2 ohms, go to next step. If resistance is not 0-2 ohms, go to step 9).
  5. Using DVOM, measure resistance of left front motor low circuit between motor pack connector (harness side) and EBCM/EBTCM connector. See WIRING DIAGRAMS . If resistance is 0-2 ohms, go to next step. If resistance is not 0-2 ohms, go to step 10).
  6. Check 6-pin ABS motor pack connector and EBCM/EBTCM connector for poor terminal contact, corrosion or damage. If connectors are faulty, go to step 11). If connectors are okay, go to next step.
  7. Reconnect ABS modulator/motor pack assembly connector. Reconnect EBCM/EBTCM connector. Test drive vehicle, obtaining speed of at least 10 MPH. Turn ignition off. Repeat drive sequence 2 more times. Using scan tool, display DTCs. If DTC C1256 sets as current in last 3 drive cycles, go to step 12). If DTC C1256 does not set as current in last 3 drive cycles, go to step 13).
  8. Replace motor pack. After repairs, perform DIAGNOSTIC SYSTEM CHECK .
  9. Repair open or high resistance in left front motor high circuit between motor pack and EBCM/EBTCM. After repairs, perform DIAGNOSTIC SYSTEM CHECK .
  10. Repair open or high resistance in left front motor high circuit between motor pack and EBCM/EBTCM. After repairs, perform DIAGNOSTIC SYSTEM CHECK .
  11. Replace all faulty terminals or connectors. After repairs, perform DIAGNOSTIC SYSTEM CHECK .
  12. Replace EBCM/EBTCM. After repairs, perform DIAGNOSTIC SYSTEM CHECK .
  13. Malfunction is not currently present. Using scan tool, select MANUAL CONTROL. While applying light pressure on brake pedal, move ABS motor of affected channel in both directions. If erratic or jumpy brake pedal movement is detected while applying and releasing ABS motor, malfunction may be intermittent. An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside insulation. If malfunction is not current, wiggle wires of affected channel and check if DTC resets. This will assist in locating an intermittent in motor circuitry or connections. Frequency of malfunction can be determined by using enhanced diagnostic function of scan tool. Check for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or damaged wiring harness. After diagnosis is complete, clear DTCs and test drive vehicle for 3 drive cycles to verify DTC does not reset. Drive cycle consists of starting vehicle, driving vehicle faster than 10 MPH, stopping vehicle, and then turning ignition off.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.