GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1998 🢒 Trans Sport Ext. 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C1257 LF ABS Motor Circuit Shorted to Ground

Object Number: 155204 Size: SF
ABS Components
Antilock Brake System Schematics
Handling ESD Sensitive Parts Notice

Circuit Description

DTC 1257 identifies an ABS motor circuit that shorts to ground. The malfunction will cause one of the following conditions to occur:

    • The ABS motor will not be controlled at the commanded current rate.
    • The driver circuit will allow current directly to the ground.

Conditions for Setting the DTC

DTC C1257 can set anytime. A malfunction exists if The EBCM/EBTCM detects an out of range voltage on either of the left front ABS motor circuits. An out of range voltage on either circuit indicates one of the following conditions:

    • A circuit shorts to ground.
    • An ABS brake motor shorts internally.

Action Taken When the DTC Sets
    • A malfunction DTC stores.
    • The ABS/TCS disables.
    • The amber ABS/TCS warning indicators turn on.

Conditions for Clearing the DTC
    • The condition responsible for setting the DTC no longer exists and the Scan Tool Clear DTC function is used.
    • 100 drive cycles pass with no DTC detected.

Diagnostic Aids

Use the Scan Tool Manual Control function in order to exercise ABS motor movement of affected channel in both directions while applying light pressure on the brake pedal. An intermittent malfunction may be indicated if erratic or jumpy brake pedal movement is detected while performing an apply or release function of the ABS monitor. Use the enhanced diagnostic function of the Scan Tool in order to measure the frequency of the malfunction. Refer to the Scan Tool manual or Scan Tool Diagnostics located in this section for the procedure. If the malfunction is not current use the following procedure to pinpoint an intermittent malfunction in the motor circuitry or connections:

  1. Wiggle the wires of the affected channel.
  2. Inspect if the DTC resets.

Thoroughly inspect any circuitry that may be causing the intermittent complaint for the following conditions:

    • Rubbed-through wire insulation
    • A broken wire inside the insulation
    • Backed out terminals
    • Improper mating
    • Broken locks
    • Improperly formed or damaged terminals
    • Poor terminal-to-wiring connections
    • Physical damage to the wiring harness

Clear the DTCs after completing the diagnosis. Test drive the vehicle for three drive cycles in order to verify that the DTC does not reset. Use the following procedure in order to complete one drive cycle:

  1. Start the vehicle.
  2. Drive the vehicle over 16 km/h (10 mph).
  3. Stop the vehicle.
  4. Turn the ignition to the OFF position.

Important: Zero the J 39200 test leads before making any resistance measurements.

Step

Action

Value(s)

Yes

No

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check

2
  1. Install a scan tool.
  2. Turn the ignition switch to the RUN position, engine off.

Does DTC C1257 occur intermittently?

--

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn the ignition switch to the OFF position.
  2. Disconnect the 6-way ABS brake motor pack connector.
  3. Disconnect the 8-way EBCM/EBTCM connector C2
  4. Use the J 39200 in order to measure the resistance between the 6-way ABS brake motor pack harness connector terminal F and ground.

Is the resistance equal to the specified value?

OL

(Infinite)

Go to Step 4

Go to Step 9

4

Use J 39200 in order to measure the resistance between the 6-way ABS brake motor pack harness connector terminal E and ground.

Is the resistance equal to the specified value?

OL

(Infinite)

Go to Step 5

Go to Step 10

5

Use the J 39200 in order to measure the resistance between the 6-way ABS brake motor pack connector terminal F and ground.

Is the resistance equal to the specified value?

OL

(Infinite)

Go to Step 6

Go to Step 8

6
  1. Inspect the following components for damage:
    2. • The 6-way ABS brake motor pack connector
    • The 6-way ABS brake motor pack harness connector
    • Damage may cause a short to ground with the connector connected.
  2. Inspect the following components for damage:
    3. • The 8-way EBCM/EBTCM connector C2
    • The 8-way EBCM/EBTCM harness connector C2
    • (Damage may cause a short to ground with the connector connected.)

Is there damage which may cause a short to ground?

--

Go to Step 11

Go to Step 7

7
  1. Reconnect the 6-way ABS brake motor pack connector.
  2. Reconnect the 8-way EBCM/EBTCM connector C2.
  3. Test drive the vehicle obtaining a speed at least 16 km/h (10 mph).
  4. Turn the ignition switch to the OFF position.
  5. Repeat the drive sequence two additional times.
  6. Use the scan tool in order to inspect for DTCs.

Did DTC C1257 set as a current DTC in the last three drive cycles?

--

Go to Step 12

Go to Step 13

8

Replace the ABS brake motor pack. Refer to ABS Motor Pack Replacement .

Is the repair complete?

--

Go to Diagnostic System Check

--

9

Repair the short to ground in CKT 1280.

Is the repair complete?

--

Go to Diagnostic System Check

--

10

Repair the short to ground in CKT 1281.

Is the repair complete?

--

Go to Diagnostic System Check

--

11

Replace all of the following components that exhibit signs of damage:

    • The terminals
    • The connectors
    • The wires
        Damage may cause a short to ground.

Is the repair complete?

--

Go to Diagnostic System Check

--

12

Replace the EBCM/EBTCM. Refer to Electronic Brake and Traction Control Module Replacement .

Is the repair complete?

--

Go to Diagnostic System Check

--

13

The malfunction is intermittent or not present at this time.

Is a concern still present?

--

Go to Diagnostic Aids

Go to Diagnostic System Check