Powertrain Control Module Controlled Tachometer Diagnosis. Cadillac Concours 1997

For 1990-2009 cars

Refer to

#### Ignition Control (IC) Module

Engine Controls Components
Fuel Pump and Relay
PCM Power and Grounds
OBD II Symbol Description Notice
ESD Notice
ESD Notice
for wiring view.

### Circuit Description

The IPC supplies 12 volts to the TACH circuit. The PCM Pulse Width Modulates (PWM) this circuit. This PWM signal varies with the speed of the engine.

### Test Description

1. Connecting a test lamp in series between battery voltage and the tach circuit to the PCM allows the PCM to create the PWM signal on the tach circuit. With normal circuit operation the test lamp will pulse while running. A higher engine speed will create a faster pulse of the test light.

2. When checking for shorts to ground, resistance of more than 10K ohms is usually acceptable although most readings should be infinite (OL).

   When checking for circuit continuity (opens) resistance should be 5 ohms or less.

   When checking for shorts to voltage take measurements with the ignition ON and OFF.

   Disconnect the circuit from all components before performing any circuit check.

   Always check or zero the meter before performing resistance checks.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to the A Powertrain On Board Diagnostic (OBD) System Check
2 | Important: Verify no PCM or IPC DTC's are set before proceeding with this diagnostic procedure. Operate the vehicle while monitoring Instrument Panel Cluster operation. Do all other IPC displays function correctly? | -- | Go to Step 3 | Go to Body Electrical

3

Important: Failure to have the engine running during the following step may cause a Vehicle Theft Deterrent DTC to set. Failure of the vehicle to start may also occur.

1. Start and idle the engine.
2. Disconnect the IPC connector containing the TACH circuit.
3. Connect a test lamp between battery positive and the tach circuit at the IPC connector (harness side).
4. Using the DMM J 39200 measure the frequency on the TACH circuit with the engine idling.

Is the frequency measured on the TACH circuit near the value specified?

22 Hz

Go to Step 4

Go to Step 5

4 | While monitoring the DMM, vary the engine speed between the RPM value range specified. Does the frequency vary with the engine speed? | Idle - 3000 RPM | Go to Step 6 | Go to Step 8

5

1. Record the fluid life indexes.
2. Turn the key OFF and wait 30 seconds.
3. Disconnect PCM connector C2.
4. Using the DMM measure the TACH circuit for a short to ground, open, short to voltage or a short to another circuit. Refer to Test Descriptions .
5. Repair the TACH circuit if needed.

Was a repair made to the TACH circuit?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 8

6

1. Check terminal contact at the IPC connector.
2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 7

7 | Replace the IPC. Refer to Body Electrical . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

8

1. Check terminal contact at the PCM connector.
2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 9

9 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --