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:

• | Ignition voltage

• | Ground

• | IC

• | Low reference

### Diagnostic Aids

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

• | A slight to moderate resistance on any IC circuit can cause a misfire before DTC P0351-P0355 sets.

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

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

#### Special Tools

J 26792 HEI Spark Tester

### Circuit/System Verification

1. Verify that the engine is in good mechanical condition before continuing with this diagnostic.
2. Verify the following conditions:

• | 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 Spark Plug Inspection and Ignition System Specifications.

### Circuit/System Testing

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

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

3. Test for less than 5 ohms between the low reference circuit terminal D and ground.

⇒ | If greater than the specified range, 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 A and ground.

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

5. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
6. Start the engine, and observe the scan tool Misfire Current Cylinder parameters.

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

7. If the circuits test normal, test or replace the spark plug/s.

### Component Testing

Use the J 26792 to verify the output of each ignition coil/module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Ignition Coil Replacement

• | Spark Plug Replacement