GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1999 🢒 Catera 🢒 DTC 🢒 DTC 21 No Speed Signal

Object Number: 377725 Size: SF

Circuit Description

The electronic brake/traction control module (EBTCM), transmits a processed vehicle speed signal (VSS) from terminal 23 to terminal 4 of the power steering control module (PSCM). The PSCM uses the speed signal and the characteristic curve programmed in the microprocessor to determine the electric current variable for the power steering fluid flow control valve actuator.

Conditions for Setting the DTC

The power steering control module detects that the vehicle speed signal (VSS) is no longer present at terminal 4.

Action Taken When the DTC Sets
    • Power steering assist will default to partial manual steering.
    • The PSCM will store a DTC 21 in memory.

Conditions for Clearing the DTC
    • Conditions for the fault are no longer present.
    • Using the scan tool.

Diagnostic Aids

Check for the following conditions if a history or intermittent DTC is indicated:

    • A poor connection at the PSCM. Inspect the harness connectors for backed out terminals, improper mating, improperly formed or damaged terminals, and poor terminal to wire connections.
    • A damaged wiring harness. Inspect the wiring harness for damage. If the wiring harness appears to be in good condition, observe the display on the DMM while moving the connectors and wiring harnesses related to the circuits. A change in the DMM display during this test will indicate the location of the fault.
    • For additional information, refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This step checks to see if the speedometer is operating properly.

    2.

  2. This step checks for the speed signal input into the power steering control module.

    3.

  3. This step replaces the power steering control module.

Step

Action

Value(s)

Yes

No

1

Was the Variable Effort Steering System Check performed?

--

Go to Step 2

Go to Variable Effort Steering System Check

2

Does the speedometer operate properly?

--

Go to Step 3

Go to Speedometer and/or Odometer Inoperative in I/P, Guages and Console.

3

  1. Disconnect the power steering control module connector.
  2. Raise the drive wheels.
  3. Turn the ignition switch to the ON position.
  4. Use the DMM, on the AC scale, to measure the voltage between terminals 4 and 8 of the power steering control module connector while rotating the LH rear wheel.

Is the measured voltage within the specified value?

Greater than 1 VAC

Go to Step 5

Go to Step 4

4
  1. Locate an open or a high resistance in circuit PA12.
  2. Repair the open or the high resistance in circuit PA12.

Is the repair complete?

--

Go to Step 6

--

5

Replace the power steering control module. Refer to Power Steering Control Module Replacement

Is the replacement complete?

--

Go to Step 6

--

6
  1. Connect all connectors and components that were disconnected.
  2. Road test the vehicle.
  3. After road test, install the scan tool again.
  4. Check for DTC 21.

Is DTC 21 present?

--

Go to Variable Effort Steering System Check

System OK