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For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Century (China) (CNG) 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C1277 Requested Torque Signal Circuit Malfunction

Object Number: 393818 Size: MF
ABS Components
Antilock Brake System Schematics
Handling Electrostatic Discharge Sensitive Parts Notice
Handling Electrostatic Discharge Sensitive Parts Notice

Circuit Description

Traction Control is simultaneously controlled by the EBTCM and the Powertrain Control Module (PCM). The PCM receives a REQUESTED TORQUE request via a Pulse Width Modulated (PWM) signal from the EBTCM requesting the desired torque level for proper Traction Control system operation. The PCM supplies the pull up voltage.

Conditions for Setting the DTC

DTC C1277 can be set when there is an open or short in the Requested Torque line between the EBTCM and PCM or there is a TCS communication malfunction detected by the PCM and indicated to the EBTCM, by broadcasting a Class 2 message.

Action Taken When the DTC Sets
    • A malfunction DTC is stored.
    • TCS is disabled.
    • Traction Control (TRAC OFF) indicator is turned on.
    • Service Vehicle Soon Indicator is turned on.
    • ABS remains functional.

Conditions for Clearing the DTC

Condition for DTC is no longer present and scan tool is used to clear the history DTC.

Diagnostic Aids
    • Possible causes for DTC C1277 to set are:
       - Requested Torque line (CKT463) open.
       - Requested Torque line (CKT463) shorted to ground.
       - Requested Torque line (CKT463) shorted to voltage.
       - Communication frequency malfunction.
       - PCM not receiving Class 2 message.
    • It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.
    • If an intermittent malfunction exists refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

Step

Action

Value(s)

Yes

No

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - ABS

2
  1. Turn the ignition switch to the OFF position.
  2. Disconnect the EBTCM connector.
  3. Install the J 39700 Universal Pinout Box using the J 39700-99 Cable Adapter to the EBTCM harness connector only.
  4. Disconnect the PCM connector C1.
  5. Using a DMM, measure the resistance between terminal C9 of Universal Pinout Box and the PCM connector C1 terminal 71.

Is the resistance within the range specified in the Value(s) column?

0-2 ohms

Go to Step 4

Go to Step 3

3

Repair CKT 463 for an open or high resistance. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

4
  1. Connect the DMM between terminals C9 and D of the Universal Pinout Box.
  2. Measure CKT 463 for continuity to ground.

Is CKT 463 shorted to ground?

--

Go to Step 5

Go to Step 6

5

Repair CKT 463 for a short to ground. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

6
  1. DMM still connected between terminals C9 and D of the Universal Pinout Box.
  2. Turn the ignition switch to the ON position, engine off.
  3. Measure CKT 463 for voltage between terminals C9 and D of Universal Pinout Box.

Is any voltage present on CKT 463 with the ignition ON?

--

Go to Step 7

Go to Step 8

7

Repair CKT 463 for a short to voltage. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

8
  1. Turn the ignition switch to the OFF position.
  2. Reconnect the PCM connector C1 to the PCM.
  3. Start the engine.
  4. Using a DMM, measure the voltage between terminals C9 and D of the Universal Pinout box.

Is the voltage within the range specified in the Value(s) column?

4.5-5.5 V

Go to Step 9

Go to Step 10

9

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

Is the replacement complete?

--

Go to Diagnostic System Check - ABS

--

10

Suspect the PCM. Refer to A Powertrain On Board Diagnostic (OBD) System Check or A Powertrain On Board Diagnostic (OBD) System Check in Engine Controls.

Is the diagnosis complete?

--

Go to Diagnostic System Check - ABS

--