For 1990-2009 cars

### Circuit Description

The 3X reference signal is produced by the ignition control (IC) module. The IC module calculates the 3X reference signal by dividing the crankshaft position (CKP) sensor 7X pulses by 2 when the engine is running and when the CKP synchronizing pulses are being received. The powertrain control module (PCM) uses the 3X reference signal in order to calculate the engine RPM and the crankshaft position at engine speeds above 1,600 ±150 RPM. The PCM also uses these pulses in order to initiate the injector pulses. The PCM compares the 3X reference pulses to the 24X CKP pulses and the camshaft position (CMP) pulses. If the PCM receives an incorrect number of pulses on the 3X circuit, a DTC P1374 will set and the PCM will use the 24X CKP reference circuit for fuel and ignition control. The engine will continue to start and run using only the 24X CKP and camshaft position sensor signals.

### Conditions for Running the DTC

The engine is running, and the 24X reference pulses are being received.

### Conditions for Setting the DTC

• | The ratio of 24X reference pulses to 3X reference pulses received by the PCM does not equal 8.

• | The ratio of 24X reference pulses to camshaft position PCM input pulses received by the PCM equals 48.

• | The conditions are present for more than 10 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

DTC P1374 can be caused by secondary components leaking high voltage into the IC module.

Inspect for the following conditions:

• | Incorrect harness routing near secondary ignition components

• | Ignition coil arcing to wiring harness or IC module--Inspect the ignition coils for the following conditions:

- | Cracks

- | Carbon tracking

- | Other signs of damage

• | Secondary ignition wires arcing to wiring harness

• | If the DTC is determined to be intermittent refer, to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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 data 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 as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

4 |

1. Install J 34730-380 injector harness load tester using load tester adapter to the multi-way fuel injector harness connector.
2. Turn ON the ignition.
3. Connect a test lamp to B+.
4. Repeatedly touch the test lamp to the low resolution engine speed signal circuit at the IC module harness connector while observing the J 34730-380 injector harness load tester.

Does the J 34730-380 injector harness load tester lamps blink?

Go to Step 8

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Turn ON the ignition.
4. Test for the following conditions:

• | 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. Refer to Wiring Repairs and Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 6

6 | Test the low resolution engine speed signal circuits for a poor terminal 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 11 | Go to Step 7
7 | Test for the following conditions:

• | Incorrect harness routing near secondary ignition components

• | Ignition coil arcing to wiring harness or IC module--Inspect the ignition coils for the following conditions:

- | Cracks

- | Carbon tracking

- | Other signs of damage

• | Secondary ignition wires arcing to the wiring harness

Did you find and correct the condition?

Go to Step 11

Go to Step 10

8 | Test for faulty terminal connections at the IC module. 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 11 | Go to Step 9
9 | Replace the IC 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 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 DTC that you have not diagnosed. | Go to Diagnostic Trouble Code (DTC) List | System OK