GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Sierra - 4WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Engine Speed Output Circuit Diagnosis

Object Number: 337310 Size: SF
Engine Controls Component Views
Cell 21: Body Control Module, Vehicle Speed Sensor
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Instrument Panel Cluster (IPC) supplies a voltage to the Engine Speed Output circuit. The PCM creates the Engine Speed Output signal by rapidly grounding this circuit via an internal switch called a driver. The other components on this circuit recognize the voltage being pulled to ground as an indication of engine speed.

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 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 I/P removal. Test the circuit from the PCM to the tachometer for being open, shorted to ground or, voltage.

    2.

  2. This step is testing for the proper signal voltage.

    3.

  3. This step is testing for an open circuit between the IPC and connector C100.

    4.

  4. This step is testing for a grounded circuit between the IPC and connector C100.

    5.

  5. This step is testing for an open circuit between the PCM and connector C100.

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 Instrument Cluster System Check in Instrument Panel, Gauges and Console.

  1. Start the engine.
  2. Monitor the tachometer at the Instrument Panel Cluster (IPC).

Does the vehicle's tachometer indicate an engine RPM?

--

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Remove the underhood electrical center cover.
  3. Remove the underhood electrical center side shield.
  4. Lift the underhood electrical center up to gain access to C100 (16 way black) connector.
  5. Disconnect the C100 connector.
  6. Turn ON the ignition.
  7. Measure the engine speed output circuit voltage from the C100 connector (female side of connector) to ground using the DMM J 39200 . Refer to Measuring Voltage in Wiring Systems.

Does the DMM display a voltage greater than the specified value?

9.5V

Go to Step 7

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Remove the IPC. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges and Console.
  3. Test continuity from the engine speed output circuit at the IPC electrical connector to connector C100. Refer to Testing for Continuity in Wiring Systems.

Does the DMM display continuity?

--

Go to Step 5

Go to Step 9

5

Test continuity from the engine output speed circuit to battery ground. Refer to Testing for Continuity in Wiring Systems.

Does the DMM display continuity?

--

Go to Step 10

Go to Step 6

6
  1. Inspect the IPC harness connector for poor connections.
  2. If you find a poor connection repair the connection as necessary.

Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

Did you find and repair the condition?

--

System OK

Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console

7

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2. Refer to Powertrain Control Module Replacement/Programming .
  3. Test the continuity of the engine speed output circuit from the PCM harness connector to connector C100 using a DMM J 39200 . Refer to Testing for Continuity in Wiring Systems.

Does the DMM display continuity.

--

Go to Step 8

Go to Step 11

8

Test the continuity of the engine speed output circuit from the PCM harness connector to ground using a DMM J 39200 . Refer to Testing for Continuity in Wiring Systems.

Does the DMM display continuity?

--

Go to Step 12

Go to Step 13

9

Repair the open engine speed output circuit from the IPC to connector C100. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

System OK

--

10

Repair the grounded engine speed output circuit from the IPC to connector C100. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

System OK

--

11

Repair the open engine speed output circuit from the PCM to C100. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

System OK

--

12

Repair the grounded engine speed output circuit from the PCM to C100. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

System OK

--

13
  1. Inspect the PCM and the C100 harness connector for poor connections. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
  2. If you find a poor connection repair the connection as necessary.

Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and repair the condition?

--

System OK

Go to Step 14

14

Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is the replacement complete?

--

System OK

--