Engine Speed Output Circuit Diagnosis. Pontiac Firebird 1999

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1999 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Engine Speed Output Circuit Diagnosis

Engine Controls Component Views
Engine Speed Output, CKP, CMP and Knock Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The 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 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 Connector Test Adapter Kit J 35616 . 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.

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 I/P is completely inoperative, refer to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console. If DTC P0645 is set do not use this diagnostic table, this table only diagnosis for an open circuit. With the engine running, does the vehicles tachometer indicate engine RPM?	--	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. Measure the Voltage from the engine speed circuit using the DMM J 39200 . Does the DMM display the specified value?	B+	Go to Step 6	Go to Step 4
4	Remove the Instrument Cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges and Console. Test the continuity of the engine speed circuit using the DMM J 39200 . Refer to Testing for Continuity in Wiring Systems. Does the DMM display continuity?	--	Go to Diagnostic System Check - Instrument Cluster in Instrument Panel Gauges and Console.	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	Inspect for poor connections at the PCM. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems. If you find a poor connection repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition?	--	Go to Step 8	Go to Step 7
7	Important: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. 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