GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC K Sierra - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 DTC P0351

Circuit Description

The enhanced ignition system uses the crankshaft position (CKP) sensor in order to provide a timing input to the control module. Ignition control (IC) spark timing for each cylinder is based on this input. The control module provides the ignition timing signal to the ignition control module (ICM) to control the ignition coil. Each timing pulse detected by the ICM allows the ICM to energize the ignition coil. A large secondary ignition voltage is induced in the secondary coil by the primary coil. This high voltage is switched to the correct spark plug by the distributor. This diagnostic trouble code (DTC) will set if the powertrain control module (PCM) detects an unusually high or low voltage on the ignition timing signal circuit.

Conditions for Running the DTC
    • The ignition control is enabled.
    • The engine speed is less than 250 RPM.

Conditions for Setting the DTC

The ignition control voltage is not within the specified range 0.04-4.9 volts.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) the first time the diagnostic runs and fails.
    • The control module will set the DTC and records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
    • A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
    • Use a scan tool in order to clear the DTCs.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if the DTC is an intermittent.

    2.

  2. This step checks if the IC timing signal from the PCM is available at theICM.

Step

Action

Values

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

  1. Clear the DTCs.
  2. Disconnect the injector harness connector.
  3. Crank the engine for 15 seconds.

Does DTC P0351 set?

--

Go to Step 3

Go to Intermittent Conditions

3

  1. Turn the ignition OFF.
  2. Reconnect the injector harness connector.
  3. Disconnect the ICM harness connector.
  4. Probe the IC timing control circuit with a DMM set to the AC scale.
  5. Crank the engine.
  6. Observe the voltage.

Does the voltage measure within the specified value?

1-4 V

Go to Step 4

Go to Step 6

4
  1. Turn OFF the ignition.
  2. Probe the ICM ground circuit at the ICM connector with a test lamp connected to B+.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 10

5
  1. Turn ON the ignition, with the engine OFF.
  2. Probe the ignition 1 voltage circuit at the ICM harness connector with a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 14

Go to Step 13

6
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector.
  3. Probe the IC timing control circuit at the PCM connector with a test lamp connected to B+.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Test for an open in the IC timing control circuit between the PCM and the ICM harness connector.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 8

8
  1. Reconnect the PCM connector.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the IC timing control circuit at the ICM harness connector with a DMM set to the DC scale and connected to ground.

Does the voltage measure more than the specified value?

1.0 V

Go to Step 12

Go to Step 9

9

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections or Connector Repairs in Wiring Systems.

Does you find and correct the condition?

--

Go to Step 16

Go to Step 15

10

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

Did you complete the repair?

--

Go to Step 16

--

11

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

Did you complete the repair?

--

Go to Step 16

--

12

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

Did you complete the repair?

--

Go to Step 16

--

13

Repair the open in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 16

--

14

Replace the ICM. Refer to Ignition Control Module Replacement .

Did you complete the replacement?

--

Go to Step 16

--

15

Replace the powertrain control module. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 16

--

16
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 17

Go to Step 2

17

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK