GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Seville 🢒 Engine 🢒 Engine Controls - 4.6L 🢒 Powertrain Control Module Controlled Tachometer Diagnosis

Circuit Description

The tachometer signal is a pulse width modulated (PWM) signal. The Instrument Panel Cluster (IPC) supplies ignition voltage to the tachometer control circuit through a pull-up resistor. The a low side driver in the PCM grounds the tachometer control circuit in relation to engine speed.

Step

Action

Values

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

Are any IPC DTCs set?

--

Go to the applicable IPC DTCs

Go to Step 3

3
  1. Start and idle the engine.
  2. Observe the IPC tachometer.

Does the IPC tachometer indicate an RPM?

--

Go to Diagnostic Aids

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Turn ON the ignition, with the engine OFF.
  4. Using the DMM, measure the voltage between the tachometer control circuit and ground.

Does the DMM display a voltage near the specified value?

B+

Go to Step 5

Go to Step 8

5
  1. Leave the PCM disconnected.
  2. Set the DMM to the 10 Amp scale.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the current between the tachometer control circuit and ground.
  5. Monitor the current reading for at least 2 minutes.

Does the DMM display a current within the specified value?

0.1-1.5 Amps

Go to Step 6

Go to Step 7

6
  1. Check for poor terminal connections at the PCM.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 10

Go to Step 9

7
  1. Turn OFF the ignition.
  2. Disconnect the IPC.
  3. Leave the PCM disconnected.
  4. Turn ON the ignition, with the engine OFF.
  5. Check the tachometer control circuit for a short to voltage.
  6. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 10

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

8
  1. Turn OFF the ignition swtich.
  2. Disconnect the IPC.
  3. Leave the PCM disconnected.
  4. Turn ON the ignition, with the engine OFF.
  5. Using the DMM, check the tachometer control circuit for an open, or a short to ground.
  6. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 10

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

9

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is action complete?

--

Go to Step 10

--

10
  1. Start and idle the engine.
  2. Observe the IPC tachometer.

Does the IPC tachometer indicate an RPM?

--

System OK

Go to Step 2