Vehicle Speed Output Circuit Diagnosis. Oldsmobile Shelby Series 1 1999

For 1990-2009 cars
Engine Controls Components
Tach, Clutch Switch, VSS Output and VSS Signal
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

### Circuit Description

Various components apply a voltage to the vehicle speed output circuit. The powertrain control module (PCM) creates the vehicle speed output signal by rapidly grounding this circuit via an internal switch called a driver. The driver operates at the same rate as the vehicle speed sensor (VSS) signal input. The various components recognize the voltage being pulled to ground as an indication of vehicle speed.

The driver supplies the ground for the component being controlled. When the PCM commands a component ON, the voltage of the control circuit should be near 0 volts. When the PCM commands the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage.

### Diagnostic Aids

Important:

• | Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

• | For any test that requires probing the PCM or component harness connectors, use the J 35616 connector test adapter kit. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Wiring Systems.

• | Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the condition, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the condition occurred.

• | For an intermittent, refer to Symptoms .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. Further circuit diagnosis may require instrument panel (IP) removal. Refer to IP cluster replacement. The circuit from the PCM to the speedometer must be tested for being open, shorted to ground or voltage. If you do not find any trouble, follow the appropriate IP diagnostic procedure.

#### Vehicle Speed Sensor (VSS) Output Circuit Diagnosis

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: If the IP is completely inoperative, refer to A Diagnostic System Check - Instrument Panel.

1. Turn OFF the ignition.
2. Raise the drive wheels.
3. Start the engine.
4. Allow the engine to idle in gear.

Does the vehicles speedometer indicate vehicle speed?

--

Go to Diagnostic Aids

Go to Step 3

3

1. Turn OFF the ignition.
2. Disconnect the PCM connector C2 located on the opposite side of the manufacturer logo. Refer to Powertrain Control Module Replacement/Programming .
3. Turn ON the ignition leaving the engine OFF.
4. Measure the voltage from the vehicle speed output circuit at the PCM harness connector, using the DMM. Refer to Measuring Voltage in Wiring Systems.

Does the DMM indicate the specified value?

B+

Go to Step 7

Go to Step 4

4

1. Turn OFF the ignition.
2. Remove the IP. Refer to IP Cluster Replacement.
3. Test the continuity of the vehicle speed output circuit between the PCM harness connector and the IP harness connector, using the DMM. Refer to Testing for Continuity in Wiring Systems.

Does the DMM indicate continuity?

--

Go to Step 5

Go to Step 6

5

1. Inspect for a poor connection at the IP. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a poor connection repair the condition as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

System OK

Go to Instrument Panel, Gauges and Console

6 | Repair the open vehicle speed output circuit between the PCM and the IP. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | --

7

1. Inspect for poor connections at the PCM. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a poor connection repair the condition as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

System OK

Go to Step 8

8 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | System OK | --