Vehicle Speed Output Circuit Diagnosis. Pontiac Firebird 2000

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2000 🢒 Firebird 🢒 Body and Accessories 🢒 Theft Deterrent 🢒 Vehicle Speed Output Circuit Diagnosis

Engine Controls Component Views
OBD II Symbol Description Notice
TCS Retard Signal, VSS Output and VSS Signal
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

Various components apply a voltage to the Vehicle Speed Output circuit. The 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 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 low (near 0 volts). When the PCM commands the control circuit to a component OFF, the voltage potential of the circuit should be high (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/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.

This step tests for a voltage to the PCM.

This step tests for a short to ground.

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 IPC is completely inoperative, refer to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console. Turn OFF the ignition. Raise the drive wheels. Start the engine. Disable the ASR/TCS systems (if so equipped). Allow the engine to idle in gear. Does the vehicles speedometer indicate vehicle speed?	--	Go to Diagnostic Aids	Go to Step 3
3	Turn OFF the ignition. Disconnect the PCM connector C2 located on the opposite side of the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming . Turn ON the ignition leaving the engine OFF. 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 8	Go to Step 4
4	Turn OFF the ignition. Remove the IPC. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges and Console. Test the continuity of the Vehicle Speed Output circuit between the PCM harness connector and the I/P 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 7
5	Test the continuity of the Vehicle Speed Output circuit between the PCM harness connector and the I/P harness connector, using the DMM connected to battery ground. Refer to Testing for Continuity in Wiring Systems. Does the DMM indicate continuity?	--	Go to Step 7	Go to Step 6
6	Inspect for a poor connection at the IPC. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If you find a poor connection repair the condition as necessary. Refer to Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition?	--	System OK	Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console
7	Repair the Vehicle Speed Output circuit for an open or short to ground. Refer to Wiring Repairs in Wiring Systems. Is the action complete?	--	System OK	--
8	Inspect for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If you find a poor connection repair the condition as necessary. Refer to Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition?	--	System OK	Go to Step 9
9	Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete?	--	System OK	--