Electronic Ignition (EI) System Diagnosis. GMC Truck Envoy

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2003 🢒 Envoy - 2WD 🢒 Brakes 🢒 Hydraulic Brakes 🢒 Electronic Ignition (EI) System Diagnosis

Circuit Description

The electronic ignition system uses an individual ignition coil for each cylinder. The powertrain control module (PCM) controls the ignition operation through six ignition control (IC) circuits. Each ignition coil is connected to the PCM, power, or ground by the following circuits:

•	The ground

•	The ignition 1 voltage

•	The appropriate IC control circuit

The PCM triggers an ignition coil by grounding the appropriate IC control circuit using information from the crankshaft position (CKP) and camshaft position (CMP) sensors.

Diagnostic Aids

•	The crankshaft position (CKP) signal is not needed to start and run.

•	Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: Remove any debris from the connector surfaces before servicing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

•	Inspect the PCM and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems.

•	For intermittent conditions, refer to Intermittent Conditions .

Test Description

The number below refers to the step number on the diagnostic table.

A few sparks, then nothing is considered no spark.

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

Are DTCs P0335 or P0336 set?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

Attempt to start the engine.

Does the engine start and run?

Go to Step 4

Go to Step 15

Observe the Misfire Current Counters parameter with a scan tool.

Does the scan tool display any Misfire Current Counters incrementing?

Go to Step 5

Go to Diagnostic Aids

Remove the ignition coil for the affected cylinder. Refer to Ignition Coil Replacement .
Install the J 26792 Spark Tester to the spark plug boot.
Attach the clamp end of the J 26792 to a good engine ground.
Observe the J 26792 .
Crank the engine.

Does spark jump the tester gap?

Go to Step 11

Go to Step 6

Turn OFF the ignition.
Disconnect the ignition coil for the misfiring cylinder.
Turn ON the ignition, with the engine OFF.
Measure the battery voltage with a DMM.
Connect a test lamp between the ignition 1 voltage circuit at the harness connector of the affected ignition coil and a good ground. Refer to Probing Electrical Connectors in Wiring Systems.
Measure the voltage from the ignition 1 voltage circuit to a good ground with a DMM. Refer to Measuring Voltage Drop in Wiring Systems.

Is the voltage within 0.50 volt of the specified value?

B+

Go to Step 7

Go to Step 15

Probe the ignition 1 voltage circuit of the affected ignition coil with a test lamp connected to the ignition coil ground circuit.

Does the test lamp illuminate?

Go to Step 8

Go to Step 16

Start the engine.
Measure the DC frequency from the IC control circuit of the respective ignition coil to a good ground.

Does the frequency measure within the specified range?

2-20 Hz

Go to Step 14

Go to Step 9

Turn ON the ignition, with engine OFF.
Measure the voltage from the IC control circuit of the respective ignition coil to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Does the voltage measure more than the specified value?

1 V

Go to Step 17

Go to Step 10

Test the IC control circuit for the following conditions:

•

An open

•	A short to ground

•	High resistance

Refer to Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 13

Exchange the spark plug with a spark plug from a non-misfiring cylinder. Refer to Spark Plug Replacement .
Install the ignition coil.
Start the engine.

Does the scan tool display that the misfire followed that spark plug?

Go to Step 20

Go to Step 12

Inspect the insulating spark plug boot and conducting spring for the following conditions:

•	Any contamination

•	Any deterioration

•	Any arching

Did you find and correct the condition?

Go to Step 21

Go to Symptoms - Engine Mechanical in Engine Mechanical

Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 19

Test for an intermittent and for a poor connection at the ignition coil. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 18

Repair the open, high resistance, or short to ground in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

Repair the open in the ignition coil ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

Repair the short to voltage in the IC control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

Replace the ignition coil. Refer to Ignition Coil Replacement .

Did you complete the replacement?

Go to Step 21

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 21

Replace the spark plug. Refer to Spark Plug Replacement .

Did you complete the replacement?

Go to Step 21

Attempt to start the engine.

Does the engine start and run?

Go to Step 22

Go to Step 2

Clear the DTCs with a scan tool.
Turn OFF the ignition for 30 seconds.
Start the engine.
Let the engine reach operating temperature.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK