GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Blazer - 4WD 🢒 DTC 🢒 DTC P0654

Circuit Description

The powertrain control module (PCM) creates the engine speed output signal by pulsing the circuit to ground. The PCM pulses the circuit at the same rate as the engine speed signal input. The PCM monitors the voltage on the engine speed signal circuit. If the PCM determines the voltage is out of the normal operating range, a DTC sets.

Conditions for Running the DTC
    • The engine speed is greater than 400 RPM.
    • The ignition voltage is greater than 6 volts, but less than 18 volts.

Conditions for Setting the DTC
    • The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
    • The above condition exists for a minimum of 5.0 seconds.

Action Taken When the DTC Sets
    • The PCM stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) does not illuminate.
    • The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

Conditions for Clearing the MIL/DTC
    • A current DTC clears when the diagnostic runs and does not fail.
    • A history DTC clears after 40 consecutive malfunction free warm-up cycles.
    • The PCM receives the clear code command from the scan tool.

Step

Action

Yes

No

Schematic Reference: Instrument Cluster Schematics

Connector End View Reference: Instrument Panel, Gages, and Console Connector End Views and Powertrain Control Module Connector End Views in Engine Controls - 4.3L

1

Did you perform the Instrument Cluster Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Instrument Cluster

2
  1. Install a scan tool.
  2. Start the engine.
  3. With the scan tool, observe the Engine Speed parameter in the PCM Engine Data 1 data list.

Does the Engine Speed parameter match the tachometer display?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the powertrain control module (PCM) connector C2.
  3. Install the J 33431-C Signal Generator and Instrument Panel Tester lead to the engine speed signal circuit at the PCM harness connector, and the other lead to a good ground.
  4. Turn the ignition ON, with the engine OFF.
  5. Set the J 33431-C to generate a tachometer signal.

Does the vehicle tachometer indicate an RPM reading?

Go to Step 5

Go to Step 4

4

Test the engine speed signal circuit for an open, for a short to voltage, or for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 6

5

Inspect for poor connections at the PCM connector. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 7

6

Inspect for a poor connection at the harness connector of the instrument panel cluster (IPC). Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 8

7

Important: Program the replacement PCM.

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 4.3L.

Did you complete the replacement?

Go to Step 9

--

8

Replace the IPC. Refer to Instrument Cluster Replacement .

Did you complete the replacement?

Go to Step 9

--

9
  1. Use the scan tool in order to clear the DTCs.
  2. Operate vehicle within the conditions for running this DTC.

Does the DTC reset?

Go to Step 2

System OK