GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Eldorado 🢒 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 low side driver in the PCM grounds the tachometer control circuit in relation to engine speed.

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

Was the IPC Diagnostic System Check performed?

--

Go to Step 3

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

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. With 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. Test for poor terminal connections at the PCM.
  2. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

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. Test the tachometer control circuit for a short to voltage.
  6. If the condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to the IPC System Check

8
  1. Turn OFF the ignition.
  2. Disconnect the IPC.
  3. Leave the PCM disconnected.
  4. Turn ON the ignition, with the engine OFF.
  5. With the DMM, check the tachometer control circuit for an open, or a short to ground.
  6. If a condition 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