For 1990-2009 cars only
Diagnostic Instructions
| • | Perform the Powertrain On Board Diagnostic (OBD) System Check prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provide an overview of each diagnostic category. |
Circuit/System Description
The engine control module (ECM) creates the tachometer signal by pulsing the engine speed signal circuit to ground at a rate of 2 pulses per engine revolution. The instrument panel cluster (IPC) converts the 2 pulses per engine revolution signal to a tachometer position indicating the engine speed. The engine speed is sent to the IPC over a discreet wire from the ECM.
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Engine Control Module Scan Tool Information
Circuit/System Verification
Engine idling, the tachometer should display engine speed.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the IPC.
- Ignition ON, test for greater than 11 volts from the tachometer circuit.
- Engine idling, test for 4-7 volts from the tachometer circuit.
- If all circuits test normal, replace the tachometer.
| ⇒ | If less than the specified range, test the tachometer output circuit for an open, or a short to ground. If the circuit tests normal, replace the ECM. |
| ⇒ | If greater than the specified range, test the tachometer output circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Engine Control Module Replacement for ECM replacement, setup, and programming.
