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
|
- Start and idle the engine.
- Observe the IPC tachometer.
Does the IPC tachometer indicate an RPM?
| --
| Go to Diagnostic Aids
|
Go to Step 4
|
4
|
- Turn OFF the ignition.
- Disconnect the PCM.
- Turn ON the ignition, with the engine OFF.
- 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
|
- Leave the PCM disconnected.
- Set the DMM to the 10 Amp scale.
- Turn ON the ignition, with the engine OFF.
- Measure the current between the tachometer control circuit and
ground.
- 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
|
- Test for poor terminal connections at the PCM.
- 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
|
- Turn OFF the ignition.
- Disconnect the IPC.
- Leave the PCM disconnected.
- Turn ON the ignition, with the engine OFF.
- Test the tachometer control circuit for a short to voltage.
- 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
|
- Turn OFF the ignition.
- Disconnect the IPC.
- Leave the PCM disconnected.
- Turn ON the ignition, with the engine OFF.
- With the DMM, check the tachometer control circuit for an open,
or a short to ground.
- 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
|
- Start and idle the engine.
- Observe the IPC tachometer.
Does the IPC tachometer indicate an RPM?
| --
| System OK
|
Go to Step 2
|
