For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit/System Description

The ignition system uses individual ignition coil/module assemblies for each cylinder. The engine control module (ECM) controls the individual coils by transmitting timing pulses on the ignition control (IC) circuit of each ignition coil/module to enable a spark event. Each ignition coil/module has the following circuits:

• | An ignition voltage circuit

• | A ground circuit

• | An IC control circuit

• | A low reference circuit

### Diagnostic Aids

• | Depending on the location in the spliced ignition voltage circuit, a slight resistance can cause a misfire or a crank/no start concern. To pinpoint this condition perform a voltage drop test on the circuit.

• | Extended engine cranking time, may foul the spark plugs with excessive fuel and cause a crank/no start condition.

• | The ECM will set a misfire DTC for a high resistance or an open on the ignition control (IC) circuits.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

• | Scan Tool Snapshot Procedure

### Circuit/System Verification

Important: Verify that the engine is in good mechanical condition before continuing with this diagnostic.

• | Observe the Engine Controls Schematic for the ignition coils/modules, and review the Ignition System Specifications and the spark plug inspection procedure to verify the following:

- | The ignition coil/modules are correctly connected

- | The proper firing order

- | The proper spark plug type

- | The proper spark plug gap and torque

- | Refer to Ignition System Specifications and Spark Plug Inspection .

• | A moderate resistance on any IC control circuit can cause a misfire.

• | Extended engine cranking time, may foul the spark plugs with excessive fuel.

• | If the engine will start, then observe the scan tool Misfire Current Cylinder parameters. This will indicate the affected ignition coil/modules, and if the condition is current.

### Circuit/System Testing

1. Ignition OFF, disconnect the ignition coil/module harness connector at the affected ignition coil/modules.
2. Ignition OFF for 90 seconds, test for less than 5 ohms of resistance between the ground circuit terminal 1 and ground.

⇒ | If greater than the specified value, test the ground circuit for an open/high resistance.

3. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal 2 and ground.

⇒ | If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

Important: If the ignition fuse is open, it will be necessary to test the spliced ignition circuits and the components for a short to ground.

4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 4 and ground.

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

5. Ignition OFF, disconnect the ECM.
6. Ignition OFF, test for less than 5 ohms of resistance between the ignition control (IC) circuit terminal 3 and the ECM.

⇒ | If greater than the specified value, test the circuit for an open/high resistance.

7. Ignition OFF, connect the ECM.
8. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
9. Start the engine, observe the scan tool Misfire Current Cylinder parameters.

⇒ | If the misfire transfers with the suspect ignition coil/module, replace as needed.

⇒ | If the misfire does not transfer with the suspect ignition coil/module, refer to the Component Testing procedures below, and replace the spark plug if necessary.

⇒ | If the misfire does not transfer with the suspect ignition coil/module, and the Component Testing procedures do not isolate a fault, replace the ECM.

### Component Testing

• | Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to Spark Plug Inspection .

• | Use the J 26792 Spark Tester to verify the output of each ignition coil/module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for ECM replacement, setup, and programming

• | Ignition Coil Replacement

• | Spark Plug Replacement