Engine 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

The powertrain control module (PCM) creates the engine speed output signal by rapidly grounding this circuit via an internal switch called a driver.

The driver supplies the ground for the component being controlled. Each driver has a fault line which the PCM monitors. 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.

For an intermittent, refer to Symptoms .

### Test Description

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

1. This step is verifying a voltage from the instrument cluster.

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 instrument panel (IP) is completely inoperative, refer to A Diagnostic System Check - Instrument Cluster. If DTC P0654 is set, do not use this diagnostic table. This table only diagnoses for an open circuit. With the engine running, does the vehicles tachometer indicate engine RPM? | -- | 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.
4. Measure the voltage from the engine speed circuit using the DMM.

Does the DMM display the specified value?

B+

Go to Step 6

Go to Step 4

4

1. Remove the instrument cluster. Refer to IP Cluster Replacement.
2. Test the continuity of the engine speed circuit using the DMM. Refer to Testing for Continuity in Wiring Systems.

Does the DMM display continuity?

--

Go to A Diagnostic System Check - Instrument Cluster.

Go to Step 5

5 | Repair the open engine speed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 8 | --

6

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 terminal as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

7 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 8 | --
8 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK