GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Body and Accessories 🢒 Body Control System 🢒 DTC P1374

Circuit Description

The 3X reference signal is produced by the ignition control module (ICM). The ICM calculates the 3X reference signal by dividing the crankshaft position (CKP) sensor 18X pulses by 3. This calculation is performed while the engine is running, and while the CKP sync pulses are being received. The powertrain control module (PCM) uses the following information:

    • The 3X reference signal in order to calculate the engine RPM, and the CKP at engine speeds above 1,200 RPM
    • The pulses on the circuit in order to initiate injector pulses
    • A constant monitoring of the number of pulses on the 3X reference circuit
    • A comparison to the number of 3X reference pulses to the number of 18 X reference pulses and CAM signal pulses being received

If the PCM receives an incorrect number of pulses on the 3X reference circuit, DTC P1374 will set and the PCM will use the 18X reference signal circuit for fuel and ignition control. The engine will continue to start and run using the 18X reference and camshaft position (CMP) PCM input signals only.

Conditions for Running the DTC

The engine has been running for more than 3 seconds.

Conditions for Setting the DTC
    • The ratio of 18X reference pulses to CAM signal pulses received by the PCM equals 36:1.
    • The ratio of 18X reference pulses to 3X reference pulses received by the PCM does not equal 6:1.
    • The above conditions are present for up to 30 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.

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation. Check for the following conditions:

    • Poor connections--Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • A damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM. Turn the ignition ON and observe a voltmeter connected to the 3X reference circuit at the PCM harness connector. Observe the voltmeter while you move connectors and wiring harnesses related to the ICM. A change in voltage will indicate the location of the malfunction.

       Important: If carbon tracking is detected on any component, replace that component and the mate.

    • Malfunctioning ignition coil--Remove the ignition coils. Inspect the ICM and coils for cracks, for carbon tracking, or for other evidence that the coil secondary circuit is arcing to the ICM or ICM wiring harness. Refer to Ignition Coil Replacement .
    • Secondary ignition wires arcing to wiring harness--Check secondary ignition wires for carbon tracking or other signs of damage.

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description

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

  1. The new PCM must be programmed.

Step

Action

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

Attempt to start the engine.

Does the engine start and continue to run?

Go to Step 3

Go to Engine Cranks but Does Not Run

3
  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, or within the parameters observed in the Freeze Frame/Failure Records.

Does the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

4
  1. Turn OFF the ignition.
  2. Disconnect the ignition control module connector.
  3. Install a J 34730-405 Injector Test Lamp at any injector harness connector.
  4. Turn ON the ignition, with the engine OFF.
  5. Connect a test lamp to B+.
  6. Repeatedly touch the test lamp to the low resolution engine speed signal circuit at the ignition control module harness connector while observing the J 34730-405 .

Does the injector test lamp blink?

Go to Step 8

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Turn ON the ignition, with the engine OFF.
  4. Check for the following conditions:
    5. • Low resolution engine speed signal circuit open
    • Low resolution engine speed signal circuit shorted to ground
    • Low resolution engine speed signal circuit shorted to voltage
  5. Repair condition as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 6

6
  1. Check the low resolution engine speed signal circuit for a poor terminal connection at the PCM.
  2. Replace loose terminal if necessary. Refer to Testing for Continuity , Testing for Intermittent Conditions and Poor Connections , Repairing Connector Terminals , and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 7

7
  1. Check for the following conditions:
    2. • Incorrect harness routing near secondary ignition components

       Important: If carbon tracking is detected on any component, replace that component and the mate.

    • Ignition coil arcing to the wiring harness or to the ignition control module
    • Ignition coils for cracks, carbon tracking, or other signs of damage--Refer to Ignition Coil Replacement .
    • Secondary ignition wires arcing to the wiring harness--Refer to Spark Plug Wire Replacement
  2. Repair the condition as necessary.

Did you find and correct the condition?

Go to Step 11

Go to Step 10

8
  1. Check for loose terminal connections at the ICM.
  2. Replace loose terminals if necessary. Refer to Repairing Connector Terminals in Wiring Systems .

Did you find and correct the condition?

Go to Step 11

Go to Step 9

9

Replace the ignition control module. Refer to Ignition Control Module Replacement .

Did you complete the replacement?

Go to Step 11

--

10

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 11

--

11
  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 12

Go to Step 2

12

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