SMU - Revised Electronic Ignition System Diagnosis
| Subject: | Revised Electronic Ignition System Diagnosis |
| Models: | 2001 Chevrolet and GMC C/K Pickup and Utility Models (Silverado, Sierra, Sierra Classic HD, C/K Classic HD, Suburban, Yukon XL) |
| 2001 Chevrolet and GMC B7 Bus Chassis and C-Series Conventional Medium Duty Models |
| with 8.1L Engine (VIN G -- RPO L18) |
This bulletin is being issued to revise the Electronic Ignition System Diagnosis in the Engine Controls-8.1L sub-section of the Service Manual. Please replace the current information in the Service Manual with the following information.
The following information has been updated within SI2000. If you are using a paper version of this Service Manual, please make a reference to this bulletin on the affected page.
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 eight individual ignition control (IC) circuits. Each bank of four ignition coils is connected to the PCM, power, or ground by the following circuits:
| • | Low reference |
| • | Chassis ground |
| • | Ignition 1 voltage |
| • | The appropriate IC circuit |
The PCM triggers an ignition coil by grounding the appropriate IC circuit using information from the crankshaft position (CKP) and camshaft position (CMP) sensors.
Diagnostic Aids
Important: A missing CMP sensor signal may cause a long crank condition.
The CKP signal must be available for the engine to start. The CMP signal is not needed to start and operate the engine. The PCM can determine when a cylinder is on either the firing or exhaust stroke by the 24X signal. The 12 volt reference circuit for the CKP and CMP sensors are shared internally in the PCM. Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.For an intermittent condition, refer to Intermittent Conditions.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Monitoring the misfire current counters determines if a fault is present.
-
A good indication that the fuse is open is all of the misfire current counters are incrementing on one side of the engine. Inspect the ignition positive voltage circuit for a grounded circuit. If the fuse is open and the ignition coil circuits are OK, inspect the injector circuits for being grounded.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls |
2 |
Does the scan tool display the engine RPM? | -- | Go to Step 3 | Go to Step 25 |
3 | Are DTCs P0335, P0336, or P0351-P0358 set? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Step 4 |
Do any of the Misfire Current counters increment? | -- | Go to Step 5 | Go to Diagnostic Aids | |
5 | Do the misfire current counters increment for most cylinders on one bank of the engine? | -- | Go to Step 11 | Go to Step 6 |
6 |
Is adequate spark present? | -- | Go to Step 31 | Go to Step 7 |
7 | Measure the spark plug wire resistance. Refer to Spark Plug Wire Inspection. Does the resistance measure near the specified value? | 460 720 ohms/ft | Go to Step 8 | Go to Step 30 |
8 |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 13 |
9 | Probe the ignition 1 voltage circuit at the ignition coil electrical connector to the ignition coil ground circuit with a test lamp. Refer to Probing Electrical Connectors in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 16 |
10 | Probe the ignition 1 voltage circuit at the ignition coil electrical connector to the ignition coil low reference circuit with a test lamp. Refer to Probing Electrical Connectors in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 24 | Go to Step 20 |
Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 12 | |
12 | Repair the open in the ignition 1 voltage circuit between the fuse block and the splice. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 34 | -- |
13 |
Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 15 |
14 | Repair the open ignition 1 voltage circuit between the splice and the ignition coil connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 34 | -- |
15 | Repair the open ignition 1 voltage circuit between the fuse block fuse and splice. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 34 | -- |
16 |
Does the test lamp illuminate? | -- | Go to Step 17 | Go to Step 19 |
17 |
Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 18 |
18 | Repair the open ground circuit between the main 8-way connector and the ignition coil connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 34 | -- |
19 | Repair the open ground circuit between the ground and the main 8-way connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 34 | -- |
20 |
Does the test lamp illuminate? | -- | Go to Step 21 | Go to Step 23 |
21 |
Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 22 |
22 | Repair the open low reference circuit between the main 8-way connector and the ignition coil connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 34 | -- |
23 | Repair the open low reference circuit between the PCM and the splice. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 34 | -- |
24 |
Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 29 |
25 |
Is the voltage near the specified value? | B+ | Go to Step 26 | Go to Step 28 |
26 | Inspect for poor connections at the CKP sensor. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 27 |
27 | Replace the CKP sensor. Refer to Crankshaft Position (CKP) Sensor Replacement. Did you complete the replacement? | -- | Go to Step 34 | -- |
28 | Test for a short to ground in the CKP sensor 12-volt reference circuit and the CMP sensor 12-volt reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 32 |
29 | Replace the ignition coil. Refer to Ignition Coil(s) Replacement. Did you complete the replacement? | -- | Go to Step 34 | -- |
30 | Replace the spark plug wire. Refer to Spark Plug Wire Replacement. Did you complete the replacement? | -- | Go to Step 34 | -- |
31 | Replace the spark plug. Refer to Spark Plug Replacement. Did you complete the replacement? | -- | Go to Step 34 | -- |
32 | Inspect for poor connections at the PCM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 33 |
33 | Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement. Did you complete the replacement? | -- | Go to Step 34 | -- |
34 | Attempt to start the engine. Does the engine start and continue to run? | -- | Go to Step 35 | Go to Step 2 |
35 |
Does the vehicle operate normally, with no MIL illumination and no stored DTCs? | -- | System OK | Go to Diagnostic Trouble Code (DTC) List |
