GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The ignition control module (ICM) controls spark timing when the engine is cranking. During this Bypass mode of operation, the ICM triggers each ignition coil in the proper sequence at a pre-calibrated timing advance. The ICM is connected directly to the powertrain control module (PCM) and includes the following circuits:

    • The medium resolution engine speed signal circuit
    • The camshaft position signal circuit
    • A low reference circuit
    • The low resolution engine speed signal circuit
    • The ignition control (IC) timing control circuit
    • The IC timing signal circuit

The PCM sends spark timing signals to the ICM on the IC timing control circuit, but during cranking the ICM grounds these signals. When the PCM begins receiving the 3X reference pulses from the ICM and the engine starts, the PCM applies 5 volts to the IC timing signal circuit allowing the ICM to switch to the IC mode of operation and respond to the spark timing signals from the PCM. The PCM monitors the IC timing control circuit for errors. If the PCM detects a fault, DTC P0350 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0350 Ignition Coil Control Circuit

Conditions for Running the DTC

    • The engine is running or cranking.
    • DTC P0350 runs continuously when the above condition is met.

Conditions for Setting the DTC

The PCM detects a fault in the IC timing control circuit for more than 9 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Test Description

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

  1. When the low resolution engine speed signal circuit is touched with the test lamp, the PCM detects engine speed and sends timing signals on the IC timing control circuit.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step  2

Go to Diagnostic System Check - Vehicle

2

  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3

  1. Turn OFF the ignition.
  2. Disconnect the ignition control module (ICM) connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the frequency from the ignition control (IC) timing control circuit, at the ICM connector, to a good ground with a DMM. Refer to Circuit Testing .
  5. Touch the low resolution engine speed signal circuit repeatedly at the ICM connector with a test lamp that is connected to battery voltage.
  6. Observe the DMM.

Does the frequency remain at the specified value when the circuit is touched?

0 Hz

Go to Step 5

Go to Step 4

4

Observe the DTC Info with the scan tool.

Is DTC P1350 also set?

--

Go to Step 8

Go to Step 11

5

  1. Connect a test lamp to battery voltage.
  2. Probe the ignition control timing control circuit at the ICM connector with the test lamp. Refer to Probing Electrical Connectors .

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 6

6

  1. Connect the test lamp to a good ground.
  2. Probe the IC timing control circuit at the ICM connector with the test lamp.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 10

7

Test the IC timing control circuit between the ICM and the powertrain control module (PCM) for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

8

Test the IC timing signal circuit between the ICM and the PCM for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

9

Test the IC timing control circuit between the ICM and the PCM for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

10

Test the IC timing control circuit between the ICM and the PCM for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

11

Test for an intermittent and poor connections at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

12

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

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

13

Replace the ICM. Refer to Ignition Control Module Replacement .

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the PCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 15

--

15

  1. Clear the DTCs with a scan tool.
  2. Turn OFF ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 16

16

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK